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New marsupials from the Eocene-Oligocene transition of the Andean Main Range, Chile
Journal of Verterbrate Paleontology
Abstract
We describe transitional Eocene–Oligocene marsupials of the Tinguiririca Fauna of the central Chilean Andes. Phylogenetic definitions of names attaching to several higher level clades of South American marsupials are proposed. Three new taxa are described: (1) a new species of Polydolops, P. abanicoi, representing the youngest polydolopoid known; (2) Klohnia charrieri, the closest known relative of the poorly known Patagonia (Colhuehuapian SALMA), which together form the nearest outgroup to the bizarre Groeberia (Divisaderan SALMA); and (3) a new didelphimorphian, Pascualdelphys fierroensis. Analysis of dental features in Klohnia helps resolve interrelationships among argyrolagoids, with Argyrolagidae (Proargyrolagus, Argyrolaginae) as closest outgroup to Groeberiidae ((Groeberia (Klohnia, Patagonia)); support for clades within Argyrolagoidea remains weak, in part due to missing data. An unsuccessful attempt to provide a phylogenetic placement for Pascualdelphys highlights the unsatisfactory state of knowledge about interrelationships among early didelphimorphians. The phylogenetic relationships of these new marsupials are permissive of, but provide little independent support for, the inferred post-Mustersan, pre-Deseadan age of the Tinguiririca Fauna. Marsupials from the central Andes of Chile reflect Paleogene South American latitudinal faunal provincialism and help to close an important temporal gap in the group's history.
... However, finds of SA Mesozoic mammals from places other than Argentina are still extremely limited and confined to scant remains in Bolivia, Brazil, Chile, and eventually Peru Mourier et al. 1986;Bertini et al. 1993;. The SA fossil record of Mesozoic mammals, close stem relatives, and their surviving lineages form isolated pieces of the larger Gondwanan puzzle, which is being gradually improved by findings in continental Africa, Madagascar, India, Australia, and Antarctica (e.g., Flannery et al. 1995;Rich et al. 1997Rich et al. , 1999Rich et al. , 2001Heinrich 1998;Flynn et al. 1999;Rich and Vickers-Rich 2004;Anantharaman et al. 2006;Goin et al. 2006;Prasad et al. 2007;Wilson et al. 2007;. ...
... Four different mammalian species have been described from the unit. The australosphenidans Asfaltomylus patagonicus and Henosferus molus , along with Ambondro mahabo from a slightly younger site in Madagascar (Flynn et al. 1999), are putatively related to Early Cretaceous taxa from Australia (Rich et al. 1997(Rich et al. , 1999(Rich et al. , 2001a and perhaps ultimately to monotremes ; but see Rich et al. 2002;Woodburne 2003;Woodburne et al. 2003;Chap. 4). ...
... Australosphenida was defined by Luo et al. (2001) based on discoveries from the last few decades in Gondwana. The group composition has been somewhat stable over the years, and includes Ambondro (Flynn et al. 1999), Ausktribosphenida (Rich et al. 1997(Rich et al. , 2001aRich and Vickers-Rich 2004), Henosferidae Rougier et al. 2007), and Monotremata (e.g., Archer et al. , 1992Archer et al. , 1993Pascual et al. 1992a, b;Flannery et al. 1995;Rich et al. 1999Rich et al. , 2001b. Together with Ambondro from the Middle Jurassic (Bathonian) of Madagascar (Flynn et al. 1999), the SA australosphenidans, Asfaltomylos patagonicus and Henosferus molus from the Early-Middle Jurassic (Toarcian-Bajocian?) of Patagonia, Argentina ) suggest that the group had already diversified and spread over much of what would become Gondwana by the mid-Mesozoic Rougier et al. 2007). ...
The sparse record of archaic Mesozoic South American mammals extends from the latest Early Jurassic to the latest Cretaceous, involving about 115 Ma, which can be further extended to about 160 Ma, including the post-K/Pg evidence. We review here the distribution, predicted time of origin, and likely place of origin for the lineages covered in the preceding chapters during that span of time and against the evolving geological backdrop of continental drift and paleogeography. Size, dental diversity, and likely dietary specializations of the Mesozoic South American mammals are discussed in the context of Mesozoic mammals in general. A few of the many surprising advances in comparative genetic and molecular evolution are discussed as part of a holistic view of early mammalian evolution to which fossils can, and should, be integrated. Social, financial, and geographical issues affecting paleontological research in South America, early mammals, in particular, are highlighted. We recognize that we are still in the early stages of development and that much of what we know about Mesozoic South American mammals is likely to be drastically altered by finds in the continent or underrepresented areas from formely Gondwanan landmasses such as Antarctica or Africa. Their scarce mammalian fossil record has hampered their full incorporation into an integrated view of early mammalian evolution. The relatively robust paleontological community present in several South American countries, relatively inexpensive nature of the discipline, and extensive outcrops are likely to ensure continuity of a synergistic research agenda. The potential for novel data, regional strengths in systematics, and the global resurgent importance of time as integral to model-based phylogenies are auspicious signs for the future of Mesozoic mammal research in South America.
... However, finds of SA Mesozoic mammals from places other than Argentina are still extremely limited and confined to scant remains in Bolivia, Brazil, Chile, and eventually Peru Mourier et al. 1986;Bertini et al. 1993;. The SA fossil record of Mesozoic mammals, close stem relatives, and their surviving lineages form isolated pieces of the larger Gondwanan puzzle, which is being gradually improved by findings in continental Africa, Madagascar, India, Australia, and Antarctica (e.g., Flannery et al. 1995;Rich et al. 1997Rich et al. , 1999Rich et al. , 2001Heinrich 1998;Flynn et al. 1999;Rich and Vickers-Rich 2004;Anantharaman et al. 2006;Goin et al. 2006;Prasad et al. 2007;Wilson et al. 2007;. ...
... Four different mammalian species have been described from the unit. The australosphenidans Asfaltomylus patagonicus and Henosferus molus , along with Ambondro mahabo from a slightly younger site in Madagascar (Flynn et al. 1999), are putatively related to Early Cretaceous taxa from Australia (Rich et al. 1997(Rich et al. , 1999(Rich et al. , 2001a and perhaps ultimately to monotremes ; but see Rich et al. 2002;Woodburne 2003;Woodburne et al. 2003;Chap. 4). ...
... Australosphenida was defined by Luo et al. (2001) based on discoveries from the last few decades in Gondwana. The group composition has been somewhat stable over the years, and includes Ambondro (Flynn et al. 1999), Ausktribosphenida (Rich et al. 1997(Rich et al. , 2001aRich and Vickers-Rich 2004), Henosferidae Rougier et al. 2007), and Monotremata (e.g., Archer et al. , 1992Archer et al. , 1993Pascual et al. 1992a, b;Flannery et al. 1995;Rich et al. 1999Rich et al. , 2001b. Together with Ambondro from the Middle Jurassic (Bathonian) of Madagascar (Flynn et al. 1999), the SA australosphenidans, Asfaltomylos patagonicus and Henosferus molus from the Early-Middle Jurassic (Toarcian-Bajocian?) of Patagonia, Argentina ) suggest that the group had already diversified and spread over much of what would become Gondwana by the mid-Mesozoic Rougier et al. 2007). ...
Dryolestoids are iconic members of the Mesozoic mammalian associations in South America. They achieved a large taxonomic diversity in this region with disparate dental and cranial morphotypes ranging from the classical role of sharp-toothed insectivores to bunodont, complex dentitions reflecting omnivore/herbivore adaptations. The South American radiation of dryolestoids, the meridiolestidans, are among the most abundant Cretaceous mammals, surviving the K/Pg mass extinction and continuing until the Miocene as minor members of the South American biotas. New specimens have been recently discovered, some of them including associated upper and lower jaws, and exceptionally preserved skulls. These high-quality fossils provide crucial intraspecific dental variation, both along the tooth row and from upper to lower, allowing critical re-interpretation of some taxa originally named on the basis of isolated teeth or very incomplete material. The Cretaceous diversity of meridiolestidans has been grossly overestimated, with taxa based on different dental positions of what was later determinied to be a single taxon. One relatively poorly known Late Cretaceous taxon, Groebertherium, shares many features with the classical Holartic dryolestoids and may represent a Late Jurassic/Early Cretaceous foundational morphology expected for meridiolestidans.
... However, finds of SA Mesozoic mammals from places other than Argentina are still extremely limited and confined to scant remains in Bolivia, Brazil, Chile, and eventually Peru Mourier et al. 1986;Bertini et al. 1993;. The SA fossil record of Mesozoic mammals, close stem relatives, and their surviving lineages form isolated pieces of the larger Gondwanan puzzle, which is being gradually improved by findings in continental Africa, Madagascar, India, Australia, and Antarctica (e.g., Flannery et al. 1995;Rich et al. 1997Rich et al. , 1999Rich et al. , 2001Heinrich 1998;Flynn et al. 1999;Rich and Vickers-Rich 2004;Anantharaman et al. 2006;Goin et al. 2006;Prasad et al. 2007;Wilson et al. 2007;. ...
... Four different mammalian species have been described from the unit. The australosphenidans Asfaltomylus patagonicus and Henosferus molus , along with Ambondro mahabo from a slightly younger site in Madagascar (Flynn et al. 1999), are putatively related to Early Cretaceous taxa from Australia (Rich et al. 1997(Rich et al. , 1999(Rich et al. , 2001a and perhaps ultimately to monotremes ; but see Rich et al. 2002;Woodburne 2003;Woodburne et al. 2003;Chap. 4). ...
... Australosphenida was defined by Luo et al. (2001) based on discoveries from the last few decades in Gondwana. The group composition has been somewhat stable over the years, and includes Ambondro (Flynn et al. 1999), Ausktribosphenida (Rich et al. 1997(Rich et al. , 2001aRich and Vickers-Rich 2004), Henosferidae Rougier et al. 2007), and Monotremata (e.g., Archer et al. , 1992Archer et al. , 1993Pascual et al. 1992a, b;Flannery et al. 1995;Rich et al. 1999Rich et al. , 2001b. Together with Ambondro from the Middle Jurassic (Bathonian) of Madagascar (Flynn et al. 1999), the SA australosphenidans, Asfaltomylos patagonicus and Henosferus molus from the Early-Middle Jurassic (Toarcian-Bajocian?) of Patagonia, Argentina ) suggest that the group had already diversified and spread over much of what would become Gondwana by the mid-Mesozoic Rougier et al. 2007). ...
Non-mammaliaform cynodonts, formerly called “mammal-like reptiles,” illustrate earlier states of the morphological architecture in the mammalian lineage. These mammalian forerunners show unique character combinations without direct counterparts among living vertebrates reflecting adaptations long lost along the millions of years of cynodont history. The fossil record from South America, originating mostly from the Middle to Late Triassic of Argentina and Brazil, is one of the most prolific worldwide. SA non-mammalian cynodonts are systematically diverse, including approximately 40 species that present great morphological disparity in skull shape, tooth morphology, pattern of tooth replacement, masticatory mechanisms, and locomotory architectures. In this chapter, we summarize the record of SA non-mammaliaform cynodonts.
... After Marshall's revision, the first extra-Patagonian remains were described (Woodburne & Zinsmeister, 1982Case et al., 1988): Antarctodolops dailyi Woodburne & Zinsmeister, 1984 and Eurydolops seymourensis Case et al., 1988, both found in Early Eocene strata from the Antarctic Peninsula. These species were considered as Polydolops by Goin & Candela (1995), but synonymized and recognized as Antarctodolops by Chornogubsky et al. (2009), who also described an additional species, A. mesetaense The most complete remains of this group came from the Early Oligocene of Chile, from where two species were described: Polydolops abanicoi Wyss, 1999 andP. mckennai Flynn &Wyss, 2004. ...
... Several dentaries with an almost complete horizontal ramus were recovered, and it can be observed that the anterior formula is not homogeneous. In K. abanicoi (Flynn & Wyss, 1999) it appears to be the most generalized, having a hypertrophied first incisor, a vestigial tooth on the dentary ridge and p2-m3 (Fig. 3B). The small tooth was interpreted as a p1 by Flynn & Wyss (1999). ...
... In K. abanicoi (Flynn & Wyss, 1999) it appears to be the most generalized, having a hypertrophied first incisor, a vestigial tooth on the dentary ridge and p2-m3 (Fig. 3B). The small tooth was interpreted as a p1 by Flynn & Wyss (1999). However, Goin et al. (2010) interpreted it as a small vestigial canine. ...
Polydolopidae is a family of Palaeogene marsupials recorded from outcrops in southern South America and the Antarctic Peninsula. They are mostly represented by skull fragments or maxillary, dentary and molar remains. A taxonomic and systematic revision is carried out with the inclusion of a phylogenetic analysis encompassing almost every polydolopid species and five marsupial species found to be related to them in previous analyses (Bonapartherium hinakusijum, Epidolops ameghinoi, Microbiotherium tehuelchum, Prepidolops didelphoides and Roberthoffstetteria nationalgeographica). The Polydolopidae was recovered as a monophyletic group, even though no resolution about its sister-group can be found. The following genera are recovered: Antarctodolops, Amphidolops, Archaeodolops, Eudolops, Hypodolops gen. nov., Kramadolops, Pliodolops, Pseudolops and two unidentified genera (Gen. et sp. indet 1 and 2). One genus and three new species are recognized. The family appeared at the beginning of the Palaeocene and disappeared during the Early Oligocene. The extinction of the group could be related to climatic deterioration in the Early Oligocene, when temperature and the humidity dropped, provoking desertification in the region where Polydolopids evolved.
... After Marshall's revision, the first extra-Patagonian remains were described (Woodburne & Zinsmeister, 1982Case et al., 1988): Antarctodolops dailyi Woodburne & Zinsmeister, 1984 and Eurydolops seymourensis Case et al., 1988, both found in Early Eocene strata from the Antarctic Peninsula. These species were considered as Polydolops by Goin & Candela (1995), but synonymized and recognized as Antarctodolops by Chornogubsky et al. (2009), who also described an additional species, A. mesetaense The most complete remains of this group came from the Early Oligocene of Chile, from where two species were described: Polydolops abanicoi Wyss, 1999 andP. mckennai Flynn &Wyss, 2004. ...
... Several dentaries with an almost complete horizontal ramus were recovered, and it can be observed that the anterior formula is not homogeneous. In K. abanicoi (Flynn & Wyss, 1999) it appears to be the most generalized, having a hypertrophied first incisor, a vestigial tooth on the dentary ridge and p2-m3 (Fig. 3B). The small tooth was interpreted as a p1 by Flynn & Wyss (1999). ...
... In K. abanicoi (Flynn & Wyss, 1999) it appears to be the most generalized, having a hypertrophied first incisor, a vestigial tooth on the dentary ridge and p2-m3 (Fig. 3B). The small tooth was interpreted as a p1 by Flynn & Wyss (1999). However, Goin et al. (2010) interpreted it as a small vestigial canine. ...
Polydolopidae is a family of Palaeogene marsupials recorded from outcrops in southern South America and the Antarctic Peninsula. They are mostly represented by skull fragments or maxillary, dentary and molar remains. A taxonomic and systematic revision is carried out with the inclusion of a phylogenetic analysis encompassing almost every polydolopid species and five marsupial species found to be related to them in previous analyses (Bonapartherium hinakusijum, Epidolops ameghinoi, Microbiotherium tehuelchum, Prepidolops didelphoides and Roberthoffstetteria nationalgeographica). The Polydolopidae was recovered as a monophyletic group, even though no resolution about its sister-group can be found. The following genera are recovered: Antarctodolops, Amphidolops, Archaeodolops, Eudolops, Hypodolops gen. nov., Kramadolops, Pliodolops, Pseudolops and two unidentified genera (Gen. et sp. indet 1 and 2). One genus and three new species are recognized. The family appeared at the beginning of the Palaeocene and disappeared during the Early Oligocene. The extinction of the group could be related to climatic deterioration in the Early Oligocene, when temperature and the humidity dropped, provoking desertification in the region where Polydolopids evolved.
... The discovery of additional, more complete remains of G. minoprioi led Pascual et al. (1994; see also Goin 1989) to reinforce the metatherian affinities of Groeberia and to recognize a new order within Marsupialia: Groeberida. Later, Flynn & Wyss (1999) carried out a phylogenetic analysis of the Argyrolagoidea, recovering Groeberidae as the sister taxon of Argyrolagidae. This taxonomy was maintained by subsequent authors (e.g. ...
... The anterior root is oval-shaped, while the posterior one is anteroposteriorly compressed. The crown of this tooth is lost; however, part of it was preserved and figured at the time of the publication by Goin (1989, figs 1-3) and was mentioned by Flynn & Wyss (1999). We reproduce this photograph in Figure 2B. ...
... Following Patterson (1952), Simpson (1970a) and Clemens & Marshall (1976), Groeberia was regarded as a marsupial by Pascual et al. (1994) who recognized the family Groeberidae and the Order Groeberida. Applying a phylogenetic analysis, Flynn & Wyss (1999) grouped groeberiids in the Superfamily Argyrolagoidea, Order Polydolopimorphia. All later authors up until Chimento et al. (2015) maintained this taxonomy. ...
With two recognized species, the extinct (late Eocene) Groeberia is periodically at the centre of systematic disputes. On the basis of its best-preserved specimen, we describe in detail the dental and functional morphology of the masticatory apparatus of Groeberia minoprioi. A review of its dental anatomy indicates that Groeberia has a tribosphenic molar pattern which confirms its therian affinities. Its dental formula of I2/1; C1/1; P3/1; M4/4 is compatible with the usual metatherian set of three premolars and four molars in the upper dentition, and with the common ‘pseudodiprotodont’ lower postcanine formula of one premolar (p3) and four molars. A cladistic analysis resulted in the inclusion of Groeberia among australidelphian metatherians, clustering with vombatiform diprotodontians in the strict consensus tree; however, these affinities require further testing. The functional morphology of the masticatory apparatus suggests distinct incisive and chewing phases. The incisive stroke was followed by a power stroke with a combination of proal and ectental motion of the jaw. Integrating the results of masticatory movements, occlusal tooth wear, infraorbital foramen size, and body mass estimations (90.2 g for G. pattersoni and 216.3 g for G. minoprioi), we suggest an omnivorous diet with a preference for plant material, like that characterizing living potoroids.
... However, the results of the current study cast doubt on whether argyrolagids (and possibly other argyrolagoids) are polydolopimorphians; I believe it more likely that argyrolagids are in fact members of Paucituberculata (see below). I follow Sereno's (2006: Rougier et al. 1998;Flynn and Wyss 1999), and I use the phylogenetic definition of Beck et al. (2014: 131), namely the least inclusive clade containing Didelphis marsupialis, Caenolestes fuliginosus, and Phalanger orientalis. Vullo et al. (2009) proposed the name Marsupialiformes for the clade corresponding to Btraditional,^more inclusive definitions of Marsupialia (e.g., Kielan-Jaworowska et al. 2004); I follow Beck's (in press-a: Table 1) definition of Marsupialiformes here, namely the most inclusive clade containing Didelphis marsupialis but not Deltatheridium pretrituberculare. ...
... A root is preserved within the alveolus in DGM 901-M, confirming that a procumbent tooth was indeed present. Although the crown of this tooth is not preserved in any E. ameghinoi specimen, it was probably very similar in morphology to the similarly-positioned tooth in the polydolopid Kramadolops abanicoi that Flynn and Wyss (1999: fig. 1) identified as p1, but which Goin et al. (2010: 86) referred to as c1 and Chornogubsky (2010) identified as ?c1. I concur with Flynn and Wyss (1999) that this tooth is p1 in K. abanicoi and also E. ameghinoi (see BComparisons with Other Taxa Currently Included in Polydolopimorphia^below). ...
... Although the crown of this tooth is not preserved in any E. ameghinoi specimen, it was probably very similar in morphology to the similarly-positioned tooth in the polydolopid Kramadolops abanicoi that Flynn and Wyss (1999: fig. 1) identified as p1, but which Goin et al. (2010: 86) referred to as c1 and Chornogubsky (2010) identified as ?c1. I concur with Flynn and Wyss (1999) that this tooth is p1 in K. abanicoi and also E. ameghinoi (see BComparisons with Other Taxa Currently Included in Polydolopimorphia^below). ...
The skull of the polydolopimorphian marsupialiform Epidolops ameghinoi is described in detail for the first time, based on a single well-preserved cranium and associated left and right dentaries plus additional craniodental fragments, all from the early Eocene (53–50 million year old) Itaboraí fauna in southeastern Brazil. Notable craniodental features of E. ameghinoi include absence of a masseteric process, very small maxillopalatine fenestrae, a prominent pterygoid fossa enclosed laterally by a prominent ectopterygoid crest, an absent or tiny transverse canal foramen, a simple, planar glenoid fossa, and a postglenoid foramen that is immediately posterior to the postglenoid process. Most strikingly, the floor of the hypotympanic sinus was apparently unossified, a feature found in several stem marsupials but absent in all known crown marsupials. “Type II” marsupialiform petrosals previously described from Itaboraí plausibly belong to E. ameghinoi; in published phylogenetic analyses, these petrosals fell outside (crown-clade) Marsupialia. “IMG VII” tarsals previously referred to E. ameghinoi do not share obvious synapomorphies with any crown marsupial clade, nor do they resemble those of the only other putative polydolopimorphians represented by tarsal remains, namely the argyrolagids. Most studies have placed Polydolopimorphia within Marsupialia, related to either Paucituberculata, or to Microbiotheria and Diprotodontia. However, diprotodonty almost certainly evolved independently in polydolopimorphians, paucituberculatans and diprotodontians, and Epidolops does not share obvious synapomorphies with any marsupial order. Epidolops is dentally specialized, but several morphological features appear to be more plesiomorphic than any crown marsupial. It seems likely Epidolops that falls outside Marsupialia, as do morphologically similar forms such as Bonapartherium and polydolopids. Argyrolagids differ markedly in their known morphology from Epidolops but share some potential apomorphies with paucituberculatans. It is proposed that Polydolopimorphia as currently recognised is polyphyletic, and that argyrolagids (and possibly other taxa currently included in Argyrolagoidea, such as groeberiids and patagoniids) are members of Paucituberculata. This hypothesis is supported by Bayesian non-clock phylogenetic analyses of a total evidence matrix comprising DNA sequence data from five nuclear protein-coding genes, indels, retroposon insertions, and morphological characters: Epidolops falls outside Marsupialia, whereas argyrolagids form a clade with the paucituberculatans Caenolestes and Palaeothentes, regardless of whether the Type II petrosals and IMG VII tarsals are used to score characters for Epidolops or not. There is no clear evidence for the presence of crown marsupials at Itaboraí, and it is possible that the origin and early evolution of Marsupialia was restricted to the “Austral Kingdom” (southern South America, Antarctica, and Australia).
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... Polydolopines are the most abundant mammal remains known to date from middle Eocene levels of the La Meseta Formation in the Antarctic Peninsula. The youngest polydolopine known, Polydolops abanicoi Flynn and Wyss, 1999, also comes from southern South America: the Termas del Flaco region in central Chile, from 3459 S. Its age has been estimated as early Oligocene (''Tinguirirican'' age;Flynn and Wyss, 1999, and references cited therein; ). There seems to be a relationship, probably trophic, between the multituberculate-like polydol- opines and southern South American and Antarctic forests where Nothofagus sp. ...
... In our present state of knowledge, we think that the inclusion of Epidolops in the Bonapartheriidae, in its own subfamily, the Epidolopinae Marshall 1982 (see Table 5), is the best systematic hy- pothesis at hand. 5. Three groups usually regarded as paucitubercu- latans (i.e., the groeberiids, argyrolagids, and patagoniids) should be recognized as part of the Polydolopimorphia (suborder Bonapartheriifor- mes) in a group of their own: the Argyrolago- idea (Table 5). Klohnia charrieri, from lower Ol- igocene levels of central Chile, was considered by Flynn and Wyss (1999) to be the closest known relative of Patagonia Pascual and Carli- ni, 1987 (Patagoniidae), and they regarded both taxa as the nearest outgroup to the Groeberi- idae. Although originally described as a pauci- tuberculatan, we find that Klohnia is, on the contrary, a very interesting polydolopimorphian. ...
... This feature is already, although incipi- ently, developed in Wamradolops. In the upper molars, the polydolopimorphian pairing of the paracone and metacone with StB and StD, to- gether with the enlargement of the metaconule forming the posterolingual corner of the teeth, is also present in Klohnia (see Flynn and Wyss, 1999: fig. 2G). ...
... This feature is also present, but to a lesser extent, in bonapartheriids. Several derived features in common between Wamradolops and the recently described, basal argyrolagoid Klohnia charrieri Flynn and Wyss, 1999, from lower Oligocene levels of central Chile are also relevant at this point, as discussed below (see ''Discussion''). These and other considerations argue in favor of the polydolopimorphian affinities of the groeberiids (and of argyrolagids and patagoniids as well, see below). ...
... Polydolopines are the most abundant mammal remains known to date from middle Eocene levels of the La Meseta Formation in the Antarctic Peninsula. The youngest polydolopine known, Polydolops abanicoi Flynn and Wyss, 1999, also comes from southern South America: the Termas del Flaco region in central Chile, from 34Њ59Ј S. Its age has been estimated as early Oligocene (''Tinguirirican'' age; Flynn and Wyss, 1999, and references cited therein; Kay et al., 1999). There seems to be a relationship, probably trophic, between the multituberculate-like polydolopines and southern South American and Antarctic forests where Nothofagus sp. ...
... Polydolopines are the most abundant mammal remains known to date from middle Eocene levels of the La Meseta Formation in the Antarctic Peninsula. The youngest polydolopine known, Polydolops abanicoi Flynn and Wyss, 1999, also comes from southern South America: the Termas del Flaco region in central Chile, from 34Њ59Ј S. Its age has been estimated as early Oligocene (''Tinguirirican'' age; Flynn and Wyss, 1999, and references cited therein; Kay et al., 1999). There seems to be a relationship, probably trophic, between the multituberculate-like polydolopines and southern South American and Antarctic forests where Nothofagus sp. ...
... Tinguirirican mammals are also known from the enigmatic Cañadón Blanco locality in Chubut, Argentina (Roth 1901(Roth , 1903Wyss et al., 1994;Bond et al., 1996), the Gran Barranca ( Madden et al., 2010), the Cachapoal River valley of central Chile ( Flynn and Wyss, 2004;Hitz et al., 2006), and from an unpublished site in the Chilean Andes at roughly the latitude of Santiago (Croft et al., 2008a). The stratotype sequence for the Tinguirirican SALMA (near Termas del Flaco) has produced a rich fauna ( Flynn et al., 2003), including sparse remains of marsupials: Klohnia charrieri (a groeberiid sensu Flynn and Wyss, 1999, or an argyrolagoid of uncertain affinities sensu Goin et al., 2010), Kramadolops (= Polydolops) abanicoi (Flynn and Wyss, 1999;Goin et al., 2010), and a form of disputed higher-level affinities, Hondonadia (= Pascualdelphys) fierroensis (Flynn and Wyss, 1999;Goin et al., 2010). Eutherians include an indaleciine (?litoptern); Pseudoglyptodon chilensis, a close sloth ally ( McKenna et al., 2006); and multiple dasypodids (Carlini et al., 2009). ...
... Tinguirirican mammals are also known from the enigmatic Cañadón Blanco locality in Chubut, Argentina (Roth 1901(Roth , 1903Wyss et al., 1994;Bond et al., 1996), the Gran Barranca ( Madden et al., 2010), the Cachapoal River valley of central Chile ( Flynn and Wyss, 2004;Hitz et al., 2006), and from an unpublished site in the Chilean Andes at roughly the latitude of Santiago (Croft et al., 2008a). The stratotype sequence for the Tinguirirican SALMA (near Termas del Flaco) has produced a rich fauna ( Flynn et al., 2003), including sparse remains of marsupials: Klohnia charrieri (a groeberiid sensu Flynn and Wyss, 1999, or an argyrolagoid of uncertain affinities sensu Goin et al., 2010), Kramadolops (= Polydolops) abanicoi (Flynn and Wyss, 1999;Goin et al., 2010), and a form of disputed higher-level affinities, Hondonadia (= Pascualdelphys) fierroensis (Flynn and Wyss, 1999;Goin et al., 2010). Eutherians include an indaleciine (?litoptern); Pseudoglyptodon chilensis, a close sloth ally ( McKenna et al., 2006); and multiple dasypodids (Carlini et al., 2009). ...
... Tinguirirican mammals are also known from the enigmatic Cañadón Blanco locality in Chubut, Argentina (Roth 1901(Roth , 1903Wyss et al., 1994;Bond et al., 1996), the Gran Barranca ( Madden et al., 2010), the Cachapoal River valley of central Chile ( Flynn and Wyss, 2004;Hitz et al., 2006), and from an unpublished site in the Chilean Andes at roughly the latitude of Santiago (Croft et al., 2008a). The stratotype sequence for the Tinguirirican SALMA (near Termas del Flaco) has produced a rich fauna ( Flynn et al., 2003), including sparse remains of marsupials: Klohnia charrieri (a groeberiid sensu Flynn and Wyss, 1999, or an argyrolagoid of uncertain affinities sensu Goin et al., 2010), Kramadolops (= Polydolops) abanicoi (Flynn and Wyss, 1999;Goin et al., 2010), and a form of disputed higher-level affinities, Hondonadia (= Pascualdelphys) fierroensis (Flynn and Wyss, 1999;Goin et al., 2010). Eutherians include an indaleciine (?litoptern); Pseudoglyptodon chilensis, a close sloth ally ( McKenna et al., 2006); and multiple dasypodids (Carlini et al., 2009). ...
Here we describe two new notoungulate taxa from early Oligocene deposits of the Abanico Formation in the eastern Tinguiririca valley of the Andes of central Chile, including a notostylopid (gen. et sp. nov.) and three basal toxodontians, cf. Homalodotheriidae, one of which is formally named a new species. The valley's eponymous fossil mammal fauna became the basis for recognizing a new South American Land Mammal “Age” intervening between the Mustersan and Deseadan of the classical SALMA sequence, the Tinguirirican. As a temporal intermediate between the bracketing SALMAs (Deseadan and Mustersan), the Tinguirirican is characterized by a unique cooccurrence of taxa otherwise known either from demonstrably younger or more ancient deposits, as well as some taxa with temporal ranges restricted to this SALMA. In this regard, two of the notoungulates described here make their last known stratigraphic appearances in the Tinguiririca Fauna, Chilestylops davidsoni (gen. et sp. nov.), the youngest notostylopid known, and Periphragnis vicentei (sp. nov.), an early diverging toxodontian, the youngest representative of the genus. A second species of Periphragnis from the Tinguiririca valley is provisionally described as Periphragnis, sp. nov., but is not formally named due to its currently poor representation. A specimen referred to Trigonolophodon sp. cf. T. elegans also is described. This taxon is noteworthy for also being reported from Santiago Roth's long perplexing fauna from Cañadón Blanco, now considered Tinguirirican in age. A phylogenetic analysis of notostylopids identifies Chilestylops as closely related to Boreastylops lumbrerensis from northern Argentina.
... Groeberia was originally described by Patterson (1952) who interpreted this taxon as belonging to caenolestoid metatherians after comparing it with other taxa, including some rodent-like prosimians. Later, Clemens and Marshall (1976) and Flynn and Wyss (1999) thought Groeberia as phylogenetically closer to diprotodont marsupials, particularly to the South American argyrolagoids. However, Simpson (1970aSimpson ( , 1970b published new materials and novel data on Argyrolagus and Groeberia, concluding what both taxa show remarkable differences, and thus placed the Groeberidae as Marsupialia incertae sedis. ...
... Although some authors interpreted Patagonia as allied with the metatherian clade Argyrolagoidea (e.g. von Koenigswald and Pascual 1990;Flynn and Wyss 1999;Goin and Abello 2013), no synapomorphies have been cited in support for this phylogenetic interpretation. Interestingly, although Pascual and Carlini (1987) included Patagonia within Metatheria, they cautiously considered that the genus could also be regarded as an extinct South American representative of the eutherian -marsupial dichotomy (Pascual and Carlini 1987). ...
... Present data matrix is also novel in the inclusion of the gondwanatherians S. ameghinoi Scillato-Yané and Pascual, 1985, G. patagonicum Bonaparte, 1986a, F. windhauseni Bonaparte, 1986b, L. miolaka Krause et al. 1997and B. bonapartei Prasad et al., 2007 We employ most of the codifications and concepts about gondwanatherian mammals proposed by Gurovich and Beck (2009). Finally, we included the argyrolagids Proargyrolagus, Hondalagus and Argyrolagus, because they belong to a metatherian group of controversial relationships which have frequently been linked to Patagonia and Groeberia (Flynn and Wyss 1999;Goin and Abello 2013). ...
Cenozoic mammalian faunas from South America contrast with those of the other continents by the great diversification of metatherian mammals. Among the later, a wide range of morphological disparity have been reported, and several bizarre mammals have been assigned to such clade, based mainly on biogeographical grounds. Outstanding examples of bizarre mammals referred to as Metatheria are the Eocene Groeberia and the Miocene Patagonia. Recent discoveries indicate that South America possessed a more diverse faunal composition than previously thought, and it became evident that many Mesozoic holdovers (e.g. australosphenidans, gondwanatherians and dryolestoids) surpassed the K/T boundary, thus forming part of the Cenozoic faunas. The Cenozoic taxa Patagonia and Groeberia exhibit several similarities with the Gonwanatheria, including rodent-like jaws with enlarged incisives, molariform cheek-teeth, anteriorly extended masseteric fossa and palinal mastication among other features. The inclusion of Gondwanatheria, Patagonia and Groeberia within an abarcative phylogenetic analysis resulted in close phylogenetic relationships among these taxa. Such hypothesis indicates that Cretaceous relics in the Cenozoic of South America were more diversified than previously thought.
... Groeberia was originally described by Patterson (1952) who interpreted this taxon as belonging to caenolestoid metatherians after comparing it with other taxa, including some rodent-like prosimians. Later, Clemens and Marshall (1976) and Flynn and Wyss (1999) thought Groeberia as phylogenetically closer to diprotodont marsupials, particularly to the South American argyrolagoids. However, Simpson (1970aSimpson ( , 1970b published new materials and novel data on Argyrolagus and Groeberia, concluding what both taxa show remarkable differences, and thus placed the Groeberidae as Marsupialia incertae sedis. ...
... Although some authors interpreted Patagonia as allied with the metatherian clade Argyrolagoidea (e.g. von Koenigswald and Pascual 1990;Flynn and Wyss 1999;Goin and Abello 2013), no synapomorphies have been cited in support for this phylogenetic interpretation. Interestingly, although Pascual and Carlini (1987) included Patagonia within Metatheria, they cautiously considered that the genus could also be regarded as an extinct South American representative of the eutherian -marsupial dichotomy (Pascual and Carlini 1987). ...
... Present data matrix is also novel in the inclusion of the gondwanatherians S. ameghinoi Scillato-Yané and Pascual, 1985, G. patagonicum Bonaparte, 1986a, F. windhauseni Bonaparte, 1986b, L. miolaka Krause et al. 1997and B. bonapartei Prasad et al., 2007 We employ most of the codifications and concepts about gondwanatherian mammals proposed by Gurovich and Beck (2009). Finally, we included the argyrolagids Proargyrolagus, Hondalagus and Argyrolagus, because they belong to a metatherian group of controversial relationships which have frequently been linked to Patagonia and Groeberia (Flynn and Wyss 1999;Goin and Abello 2013). ...
Cenozoic mammalian faunas from South America contrast with those of the other continents by the great diversification of metatherian mammals. Among the later, a wide range of morphological disparity have been reported, and several bizarre mammals have been assigned to such clade, based mainly on biogeographical grounds. Outstanding examples of bizarre mammals referred to as Metatheria are the Eocene Groeberia and the Miocene Patagonia. Recent discoveries indicate that South America possessed a more diverse faunal composition than previously thought, and it became evident that many Mesozoic holdovers (e.g. australosphenidans, gondwanatherians and dryolestoids) surpassed the K/T boundary, thus
forming part of the Cenozoic faunas. The Cenozoic taxa Patagonia and Groeberia exhibit several similarities with the Gonwanatheria, including rodent-like jaws with enlarged incisives, molariform cheek-teeth, anteriorly extended masseteric fossa and palinal mastication among other features. The inclusion of Gondwanatheria, Patagonia and Groeberia within an abarcative phylogenetic analysis resulted in close phylogenetic relationships among these taxa. Such hypothesis indicates that Cretaceous relics in the Cenozoic of South America were more diversified than previously thought.
... The transition from the Eocene to the Oligocene epoch marked a pronounced change in South American metatherian faunas and the beginning of the Late South American Phase of faunal evolution (Goin et al. 2012;Croft 2016). Groups last recorded during the early Oligocene include polydolopid and rosendolopid polydolopimorphians, as well as caroloameghiniid and sternbergiid didelphimorphians, whereas groups first recorded during this interval include argyrolagoids (other than Groeberia from Divisadero Largo, the age of which is uncertain but seems to be middle Eocene-López 2010), notable for their hypsodont dentitions, and several families of paucituberculatans (Flynn and Wyss 1999;Flynn et al. 2003;Goin et al. 2010;Abello 2013;Abello et al. 2018). This shift in metatherian faunas (and other South American mammals) associated with the Eocene-Oligocene Transition has been termed the Patagonian Hinge ("Bisagra Patagónica" in Spanish- Goin et al. 2012). ...
... They may have occupied ecological niches similar to extant jerboas (Dipodidae) and kangaroo rats (Heteromyidae-Simpson 1970), with suggestions that the lack of extant rodents filling similar niches in South America was attributable to the occupation of these niches by argyrolagoids until relatively recently (Mares 1975(Mares , 1985. The affinities of argyrolagoids have proven controversial; some authorities have placed them in the superfamily Argyrolagoidea in the order Polydolopimorphia Forasiepi et al. 2014;Chornogubsky and Goin 2015), which includes dentally somewhat similar (i.e., hypsodont or hypselodont) taxa such as groeberiids and patagoniids (Flynn and Wyss 1999;Goin et al. 2010), whereas others have concluded that they are members of Paucituberculata (Sánchez-Villagra 2001; Beck 2017b). The survival of argyrolagoids into the Pliocene means that it may be possible to obtain ancient proteins (such as collagen) from their fossils (Rybczynski et al. 2013), which should help clarify their phylogenetic relationships. ...
Marsupials and their fossil relatives, which collectively comprise Metatheria, have been of scientific interest for centuries, with many aspects of their evolution and systematics subject to intense research and debate. Here, we review progress over the last 25 years, which has included the description of many new species (modern and fossil), and major improvements in understanding of their phylogenetic relationships, as well as the overall evolutionary history and biogeography of Marsupialia (crown-clade) and Metatheria (total-clade). Significant advances have included the deployment of increasingly sophisticated molecular, morphological, and total evidence analyses, which have resolved most previously disputed relationships among and within the modern marsupial orders. A broad systematic consensus is now emerging, although several major areas of contention remain, particularly among fossil metatherians. New modern species continue to be described at an impressive rate, with almost 50 named in the last 25 years, and many more await discovery. There has also been an explosion in the discovery and description of fossil marsupials and non-marsupial metatherians (~270 species), principally from Australasia and the Americas but also from Antarctica, Europe, and Asia. Most are represented by dental specimens only, but some consist of complete and well-preserved material, which has led to major improvements in our understanding of the evolution of cranial and postcranial morphology. Improvements in the fossil record and advances in methods for inferring divergence times have helped clarify when and where key events occurred in metatherian evolution, and the patterns of subclade diversification. We also have improved understanding of biogeographical relationships among metatherians on different landmasses. Despite enormous progress, numerous key uncertainties remain due to major gaps in the fossil record (e.g., Antarctica, Late Cretaceous, and early Paleogene of Australia) and a comparative lack of studies that directly combine molecular and fossil data. Future advances will largely depend on improvements in the fossil record and studies that better integrate neontological and paleontological evidence. Los marsupiales y sus parientes fósiles, que en conjunto forman el grupo Metatheria, han sido de interés científico durante siglos, con muchos aspectos de su evolución y sistemática sujetos a intensas investigaciones y debates. Aquí se resumen los avances alcanzados durante los últimos 25 años, los cuales incluyen la descripción de muchas especies nuevas (tanto fósiles como actuales), una mayor comprensión de relaciones filogenéticas, y también la historia general evolutiva y biogeográfica de Marsupialia (clado corona) y Metatheria (clado completo). Los mayores avances han incluido el uso de análisis moleculares, morfológicos y de evidencia total que son cada vez más sofisticados. Dichos avances ya han resuelto muchas de las relaciones anteriormente disputadas fuera y dentro de los ordenes de marsupiales actuales. Actualmente está surgiendo un amplio consenso general, a pesar de que aún quedan varias áreas importantes de discusión. Se continúa describiendo especies nuevas actuales a una velocidad impresionante, con casi 50 nombradas en los últimos 25 años, y muchas más esperan a ser descubiertas. También ha habido una explosión en el descubrimiento y descripción de especies fósiles de marsupiales y metaterios no-marsupiales (~270 especies), principalmente de Australasia y las Américas, pero
... The lower incisors of this taxon are hypselodont but recumbent. The first argyrolagoid with hypselodont and procumbent lower incisors is Klohnia charrieri from the early Oligocene of central Chile (Flynn & Wyss 1999). Additional remains of Klohnia are known from the early Oligocene of Patagonia, Argentina . ...
... Other metatherians with procumbent lower incisors are the polydolopids, such as Kramadolops abanicoi (Flynn & Wyss 1999). However, they differ from specimen IBIGEO-P 48 and the remaining Argyrolagoidea in that their incisors are non-hypselodont. ...
The Quebrada de Los Colorados Formation (Los Cardones National Park, Salta Province, north-western Argentina), is an Eocene–Oligocene unit well represented in the Calchaqu�ı Valley area. Here we describe a new metatherian association recorded from the base of this formation, inferred as middle Eocene. Represented taxa are: Sparassodonta, family indet.: Patene simpsoni; Polydolopimorphia, Bonapartheriiformes, Argyrolagoidea: family, genus, and species indet.; and Bonapartherioidea, Prepidolopidae: Punadolops alonsoi and Coloradolops cardonensis gen. et sp. nov. Patene simpsoni is also found in the Tonco Valley, near Los Cardones, and at S~ao Jos�e de Itabora�ı, Rio de Janeiro, Brazil. Punadolops alonsoi was originally described from the Geste Formation in Salta and Catamarca provinces. Hitherto, no other Argyrolagoidea have been found in north-western Argentina in the Palaeogene. Coloradolops cardonensis is unique to the locality and levels here described. The preservation of part of the skull constitutes the best prepidolopid remains known. North-western
Argentina is a key region for the study of the evolution of South American mammals, since it has a singular geographical location between the Neotropics and the southernmost part of South America. Due to biogeographical constraints, it may lead to a better comprehension of the continental distribution of metatherian lineages during Cenozoic times.
... The procedure of identifying clades through cladistic analysis has been declared by "phylogenetic taxonomists" to be distinct from their proposed "definitional" procedure of labeling with names. The latter procedure is said to have the merit of taxonomic stability, no matter what future research reveals (e.g., Flynn & Wyss 1999). In some ways, such claims go beyond the goals of the much maligned eclectic practices of "evolutionary taxonomists". ...
... Rooting of taxa in stems should require, in our view, some biological statements about the taxonomic properties (and perhaps something of their fate) in the descendants. Flynn & Wyss (1999) present real node-based concepts of marsupial taxa (in spite of the mixed and complex terminology they employ) that are the direct outcome of taxogram practice. This method, through parsimony, attempts to render the spatiotemporal adaptive history of lineages into a monotonic construct of ever shifting taxograms. ...
... Trigonostylops) that presents similarities with the Casamayoran T. wortmanii. The marsupial Groeberia is related to the Chilean genus Klohnia from Tinguiririca (early Oligocene) and the genus Patagonia from the early Miocene of Chubut (Pascual and Carlini, 1987;Flynn and Wyss, 1999), within the Family Groeberiidae (considered as Order Groeberida by Pascual et al.,1994). Even though Groeberia minoprioi and G. pattersoni (exclusively from the Divisadero Largo Formation) do not indicate any accurate age considering the long temporal range of the family, they are the most basal taxa of this group, compatible with an age older than that of Tinguiririca (Flynn and Wyss, 1999). ...
... The marsupial Groeberia is related to the Chilean genus Klohnia from Tinguiririca (early Oligocene) and the genus Patagonia from the early Miocene of Chubut (Pascual and Carlini, 1987;Flynn and Wyss, 1999), within the Family Groeberiidae (considered as Order Groeberida by Pascual et al.,1994). Even though Groeberia minoprioi and G. pattersoni (exclusively from the Divisadero Largo Formation) do not indicate any accurate age considering the long temporal range of the family, they are the most basal taxa of this group, compatible with an age older than that of Tinguiririca (Flynn and Wyss, 1999). All these taxonomic changes support a much older age for the 'Divisaderan' fauna than previously thought. ...
... erior, separados de las otras piezas dentarias por un diastema. Los molariformes (M 1 o P 3 ) de tamaño normal . Los molariformes sublinguales no multicuspidados, con el paracónido antero-externo. La mandíbula se presenta muy corta y alta y fundida en la sínfisis. El proceso coronoide es fuerte y con una amplia fosa mesentérica (Paula Couto, 1979). & Wyss, 1999 Materiales y procedencia: Una mandíbula derecha con parte de las piezas dentarias P 3 – M 3. Otros materiales referidos son piezas dentarias y fragmentos de premaxilar y también maxilares . Zona centro, valle del río Tinguiririca, Termas del Flaco, Formación Abanico. ...
... Son marsupiales con especialización sectorial de los P 2 y P 3 y el P 3 . El M 1 es trigónido. Los incisivos son pequeños. El canino inferior está bien desarrollado. Cráneo en que los arcos zigomáticos y el rostro se presentan anchos. Paladar perforado. Mandíbula con sínfisis sin fusionar y proceso angular fuerte (Soria, 1990). & Wyss, 1999 Materiales y procedencia: Los restos fósiles corresponden a una rama mandibular izquierda con el canino. Zona centro, dos kilómetros al noroeste de Termas del Flaco, Región del Libertador Bernardo O'Higgins. Formación Abanico. Orden Didelphimorphia Gill, 1872, Para efectos de este trabajo se consideró que los caracteres presentados por ...
Introducción Los mamíferos representan uno de los últimos clados de vertebrados, en el que se observa el desa-rrollo de innovaciones anatómicas que los diferen-cian de otros grupos de vertebrados, permitiendo agruparlos en una clase propia, Mammalia. Las innovaciones más conspicuas están representadas por el desarrollo de una cubierta pilosa y la produc-ción de leche destinada a la alimentación de las crías (Kardong, 1999). A nivel óseo existen varios elementos únicos que son propios de esta clase. El más notable es la presencia de un dentario, como pieza íntegra de la totalidad de la mandíbula, que articula mediante una unión craneomandibular que comprende el cóndilo dentario y la unión escamosa glenoidea. De acuerdo a Luo et al. (2002) la defini-ción de mamífero se considera desde el ancestro inmediato a Sinocodon. El registro fósil para este grupo es conocido desde hace poco más de 200 mi-llones de años, durante el Triásico superior (Alfé-rez, 1990), alcanzando su mayor expresión durante Estado actual del conocimiento de los mamíferos fósiles de Chile
... Be it as it may, the preliminary faunal list of TAR-01 points to an early Oligocene age, based on the co-occurrence of undisputable prepidolopid/polydolopid and argyrolagoid polydolopimorphian metatherians. Such a co-occurrence was only attested in early Oligocene assemblages from Chile and Argentina thus far (Tinguirirican South American Land Mammal Age; Flynn & Wyss, 1999;Goin et al., 2010). TAR-01 was deposited by a low-energy fluvial stream, as consistently attested by sedimentological evidence (sandy channel with millimetre-sized carbonate nodules and blue clayish matrix) and its palaeontological content (charophytes, freshwater malacofauna and ichthyofauna, and putative gharial caimans). ...
... The Tinguirirican is currently regarded as temporally interposed between the Mustersan (late Eocene) and Deseadan (late Oligocene-early Miocene) intervals of the classical SALMA sequence, given that the Divisaderan, originally considered to precede the Tinguirirican, has recently been shown to be invalid as it represented a mixed assemblage of demonstrably older (mainly Casamayoran) and younger (Deseadan to Santacrucian) taxa (Cerdeño et al., 2008;López, 2008López, , 2010López and Manassero, 2008). Following a preliminary accounting (Wyss et al., 1994), various components of the Tinguiririca Fauna have been described in detail elsewhere, including its marsupials (Flynn and Wyss, 1999), interatheriids (Hitz et al., 2000(Hitz et al., , 2006, archaeohyracids Reguero et al., 2003), tardigrades (McKenna et al., 2006), dasypodids (Carlini et al., 2009), rodents (Bertrand et al., 2012), and notostylopids and basal toxodontians (Bradham et al., 2015). Here we build on this documentation, describing the fauna's diverse but sparsely represented notohippids and leontiniids. ...
Here we describe three new notohippid notoungulate species from the early Oligocene-aged Tinguiririca Fauna (Tinguirirican SALMA), recovered from volcaniclastic deposits of the Abanico Formation in the central Chilean Andes, two of which are known from material sufficiently complete to warrant formal naming. These include Eomorphippus bondi, sp. nov., a form of moderate size distinguished by hypsodont incisors and cheekteeth, as well as distinctive proportions of the upper incisors. A closely similar but more diminutive form is described as Eomorphippus neilopdykei, sp. nov. A third previously unrecognized notohippid in the Tinguiririca Fauna, best represented by a large, low-crowned, lower incisor battery, almost certainly represents a new taxon, but remains too fragmentary to warrant naming now. We also propose a new binomial for a previously named notohippid, ?Eomorphippus pascuali, originally described from Gran Barranca in Argentina but which is now also recorded in Chile. This taxon, here named Rosendo pascuali, is markedly less hypsodont than E. bondi and E. neilopdykei and retains lingual cingula on at least p4-m1. As least one leontiniid notoungulate occurs in the Tinguiririca Fauna, Termastherium flacoensis, gen. et sp. nov., best represented by two partial upper cheek toothrows and a tentatively referred maxillary fragment bearing three deciduous teeth. Collectively, description of these new fossils from Termas del Flaco, Chile helps to more fully characterize the Tinguiririca Fauna, facilitating correlation and comparison to other South American land mammal faunas spanning the Eocene-Oligocene transition.
... Be it as it may, the preliminary faunal list of TAR-01 points to an early Oligocene age, based on the co-occurrence of undisputable prepidolopid/polydolopid and argyrolagoid polydolopimorphian metatherians. Such a co-occurrence was only attested in early Oligocene assemblages from Chile and Argentina thus far (Tinguirirican South American Land Mammal Age; Flynn & Wyss, 1999;Goin et al., 2010). TAR-01 was deposited by a low-energy fluvial stream, as consistently attested by sedimentological evidence (sandy channel with millimetre-sized carbonate nodules and blue clayish matrix) and its palaeontological content (charophytes, freshwater malacofauna and ichthyofauna, and putative gharial caimans). ...
We describe claw fragments of fossil primary freshwater crabs from three areas in the Amazon
basin, Tarapoto (Early Oligocene) and Contamana (Middle Eocene to early Late Miocene) in Peru,
and Eirunepé (Late Miocene) in Brazil. All these fragments most likely belong to the family
Trichodactylidae. We show a continuous presence of primary freshwater crabs in proto-Amazonian
lowlands from the Middle Eocene to the Late Miocene and can thus shift the earliest appearance date
of freshwater-adapted brachyurans into the Eocene, at least in the Neotropics.
... The two rodent species are noteworthy in being the earliest recorded members of that clade in South America Wyss et al., 1994;Croft et al., 2008;Flynn and Wyss, 1998). Approximately half of the species from this locality have been described in detail (Flynn and Wyss, 1999;Hitz et al., 2000;Croft et al., 2003a;Reguero et al., 2003;McKenna et al., 2006;Carlini et al., in review); current systematic efforts focus on the fauna's four notohippids, including two hypsodont (high crowned) and two brachydont (low crowned) forms . ...
... The two rodent species are noteworthy in being the earliest recorded members of that clade in South America ( Wyss et al., 1994;Croft et al., 2008;. Approximately half of the species from this locality have been described in detail (Flynn and Wyss, 1999;Hitz et al., 2000;Croft et al., 2003a;Reguero et al., 2003;McKenna et al., 2006;Carlini et al., in review); current systematic efforts focus on the fauna's four notohippids, including two hypsodont (high crowned) and two brachydont (low crowned) forms ). ...
Introduction
The early theropod ancestors of birds were cursorial (runners). The central digits 2, 3 and 4 of the foot were longest, with outer digits 1 and 5 reduced (Fig. 1A). Digit 1 lost its proximal epiphysis, no longer articulating to the ankle, but rather to a fossa on the medial side of metatarsal II by means of a non-synovial joint (Middleton, 2001). In early theropods, this attachment site is found at about mid-length of metatarsal 2; digit 1 did not touch the ground (and thus is generally absent in fossil prints). In birds, the perching digit 1 is found towards the distal end of metatarsals and is opposable (Fig. 1A). The reversed orientation of the perching digit in birds is mostly due to the twisted shape of its reduced metatarsal (Middleton, 2001). Early theropods lack this torsion, indicating digit 1 had a similar orientation to other digits. Archaeopteryx represents the intermediate condition; the position of digit 1 on metatarsal 2 is distal, but the orientation of digit 1 is only slightly different than other digits (Mayr et al., 2005). Confuciusornis is the earliest bird lineage that already has a “modern”, fully opposed distal perching digit (Chiappe, 2002). We studied the development of position and orientation of the perching digit in the chicken. As in early theropods, after being at about mid-length of metatarsal 2, digit 1 becomes distally allocated, and finally changes orientation, becoming opposed to other digits (Fig. 1B). The change to a distal position may occur because the digit itself is moving along metatarsal 2; alternatively, the metatarsals may exhibit greater growth towards their proximal end, leading to the same end result. To test this, we fate-mapped the early metatarsals by labeling cells in proximal, mid and distal regions. We also inserted fragments of tantalium foil at mid-length of early metatarsals and observed their position at later stages. Our evidence is consistent with a greater growth of metatarsals towards the proximal end. We suggest a single evolutionary event in the lineage leading to birds was responsible for both metatarsal elongation and the distal position of digit 1.
Materials and methods
Examination of chicken foot development. The development of the chicken foot was observed between days 6-13 of incubation by means of whole-mount clearing and staining for cartilage using alcian blue, following the technique of Wassersug (1976). Non-prepared embryos were also photographed to observe soft tissue traits such as interdigits and epidermal pads on the ventral side of digits.
Fate mapping of early metatarsal cells. DiI is a lipophilic die that does not diffuse from the site of injection (Vargesson et al., 1997). Injections were carried out at days 6 and 7 of incubation with a pedal-activated microinjector and a glass needle. Eggs were windowed at days 3 or 4. At day 7 special care must be taken not to pierce the irrigated amnios. PBS was added to ply apart the irrigated amnios from the eggshell to get to the non-irrigated region below. For adequate identification of the position of early DiI injections, camera lucida drawings were made of the chicken foot at days 6 and 7 but were incompletely cleared revealing the contours of both metatarsals and soft-tissue. The position of each injection was marked onto a photocopy of the drawing. The final destiny of cells injected at day 6 and 7 was observed and photographed at day 9 with a rhodamine fluorescence stereomicroscope (Fig. 2A). Tantalium foil fragments were inserted at mid length of metatarsal 3 at day 6; final position of the inserted barrier was observed at days 9 and 10.
Results
Development of position and orientation of the avian perching digit. At day 6 of incubation, digit 1 is found at about mid-length of metatarsal 2 (Fig. 1B). This position becomes more distal and is already at the same position as other digits by day 8. At day 8, epidermal pads are observable on the ventral surface of digits indicating an orientation similar to that of other digits. The ventral side is oriented towards medial (“inwards”) at day 9; the digit has reversed completely by day 10.
The fate of proximo-distal metatarsal regions. The resulting fate map shows that cells in the middle and distal segment of the day 6 metatarsal were always found to be distally located at day 9, in proximity to digit 1. Cells injected in the proximal segment of day 6 metatarsals allocate to mid-proximal positions at day 9 (Fig. 2B). At day 7, injections in distal, mid and even proximal region of the metatarsal were found in the distal region at day 9 (Fig. 2C). Fragments of tantalium foil that were inserted at mid-length of metatarsal 6 were found distal at day 9, in proximity of digit 1 (Data not shown).
Discussion
The results of fate-mapping and tantalium foil insertions are consistent with the hypothesis that metatarsals grow in length asymmetrically, with greater growth towards the proximal end. This conclusion is also consistent with the phenotype of the shankless chicken mutant, which develops short metatarsals. In shankless, digit 1 is found at mid-length of metatarsal 2 (Smith et al., 2000). The distal position of digit 1 in Archaeopteryx is accompanied by metatarsals that are proportionally longer (Fig. 1A). Our developmental data suggests that metatarsal elongation in the bird lineage occurred by greater proximal growth, leading simultaneously to a distally positioned digit 1, rather than these being two separate evolutionary events. This distal position conceivably facilitated the subsequent evolution of perching
... Si bien es cierto que entre los marsupiales sudamericanos existen casos de pérdida del m4, estos son muy contados, ocurriendo sólo entre los Polydolopimorphia: los polidolópidos Polidolopinae (Marshall, 1982b), el prepidolópido Punadolops (Goin et al., 1998) y los argirolagoideos Klohnia (Flynn y Wyss, 1999) y Patagonia (Pascual y Carlini, 1987). Por el contrario, la pérdida de al menos un premolar en la fórmula postcanina de los Eutheria es común a muchos grupos. ...
This work is the first, of a series of three, taxonomic reviews of the Early Miocene (Colhuehuapian Land-mammal Age) South American metatherians. Colhuehuapian levels from the Gran Barranca south of the Colhue Huapi lake (Sarmiento Department, Chubut Province, Argentina) are the richest ones in specimens of this age. Colhuehuapian landscapes from Central Patagonia developed in a coastal plain located in a peninsular area, which originally suffered an intense erosion and subsequentely was agradded with fluvial and loessic (eolian) sediments. Palinomorphs and phytoliths suggest a period characterized by significant environmental changes, from xeric (middle Early Miocene) to humid-warm conditions (late Early Miocene). In uplands or areas far from the sea, temperate-humid dosed forests prevailed, but in lowlands or litoral areas herbaceous (grass) plants and shrubs dominated, with subordinated or patchy arboreal vegetation. Paleodimate would have been warm-temperate to warm and probably subhumid, more rainy in highlands. The most important results of this analysis are: (1) the oldest record of Didelphoidea didelphimorphians, including, probably, the oldest known caluromyid; (2) the recognition of a great diversity of carnivores belonging to the Order Sparassodonta, induding the oldest record of a Thylacosmilidae; (3) the recognition of a new species of the incertae sedis mammal Necrolestes. Among the taxa reviewed here we describe the new species Necrolestes mirabilis.
... ; Sanchez-Villagra and Kay 1997;Flynn and Wyss 1999;Sánchez-Villagra 2001;Goin 2003;Flynn and Wyss 2004;Goin et al. 2010;).Nevetheless, regardless of exactly which locus the gliriform incisor represents in paucituberculatans and diprotodontians, recent published morphological, molecular and total evidence analyses consistently indicate that Paucituberculata is not the sister-taxon of Diprotodontia, but instead falls outside Australidelphia (e.g.Amrine-Madsen et al. 2003;Horovitz and Sánchez-Villagra 2003;Asher et al. 2004;Baker et al. 2004;Nilsson et al. 2004, 2010 -seeFigure 11;Munemasa et al. 2006;Phillips et al. 2006;Beck 2008a;Beck et al. 2008b ...
I present a comprehensive overview of our current understanding of the phylogeny of Metatheria, focusing on recent studies that have presented algorithmic analyses of character matrices. I discuss the position of Metatheria within Mammalia, relationships among the various fossil metatherian groups currently known, and relationships within the metatherian crown-clade (Marsupialia). I also discuss evidence regarding divergence times within Marsupialia, I propose broad constraints on the timing of divergences between the modern orders based on the fossil record, and I summarise divergence time estimates from recent “molecular clock” studies. I conclude with a brief discussion regarding the prospects for improving our understanding of metatherian phylogeny.
... c. Study region between 33° S and 36° S, with indication of the main river valleys, and localities cited in text. 1994FLYNN & WYSS 1999 press), (2) 40 Ar/ 39 Ar age determinations on fossiliferous and associated stra tigraphic levels as well as intrusive bodies cutting the stratified series (WYSS et al. 1993KAY & KURTZ 1995 ;CHARRIER et al. 1996CHARRIER et al. , 1997CHARRIER et al. , 2002aKURTZ et al. 1997;GANA & WA LL 1997;FUENTES et al . 2002), (3) trace and rare earth element data from Oligo-Miocene lavas and intrusives (NYSTROM et al. 1993;KAY & KURTZ 1995 ;VERGARA et al. 1999), ( 4) detailed studies of the low grade meta-morphic mineral associations at several localities (LEVI et al. 1989;VER GARA et al. 1993;CARRASCO 2000), and (5) fission-track ages of late Ceno zoic intrusive bodies emplaced in Mesozoic and Cenozoic series of the Principal Cordillera (CEMBRANO et al. 2003;MAKSAEV et al. 2003). ...
The main volcanic Cenozoic deposits in the cordillera of Central Chile (33°-36°S) correspond to the middle?-late Eocene to early Miocene Abanico Fm., and the early-middle Miocene Farellones Fm. The wide distribution of the Abanico Fm., its great thickness, the frequent and thick lacustrine intercalations, the unconformable stratigraphic relation with underlying units, and its tectonic features suggest deposition in an extensional basin that underwent subsequent tectonic inversion. This interpretation is supported by recent field observations, and geochronologic, geochemical, and thermal maturity data. Extensional basin development began before 36 Ma, while the crust was relatively thin, and went on during Oligocene. Contraction occurred during and following late depositional stages of the Abanico Fm. and was controlled by inversion of extensional faults associated with basin development. This event began before 21 Ma, ended at ∼ 16 Ma, was not simultaneous throughout the region, and coincided with a thickened crust. Sedimentation and volcanism continued throughout the contractional episode along the axis of the preexistent basin and formed the Farellones Fm., while the inverted and exhumed west and east parts of the Abanico Fm. were eroded. This situation explains the absence of a clear structural boundary between the two formations at some localities, the existence of one or more angular unconformities at various localities, and that radioisotopic dates for the Abanico Fm. at some regions are younger than those obtained in low levels of the Farellones Fm. in other regions. The extensional and contractional episodes coincide with periods of slow and rapid convergence rates between the Nazca Plate and South-America respectively. The oldest ages for the base of the Farellones Fm. (25 and 21 Ma) were obtained to the north of the study region, and the youngest ages for the Abanico Fm. (16.1 Ma) to the south of it suggesting a N to S progression of deformation. This can be attributed to the southward progression of the intersection of the Juan Fernández Ridge with the continental margin.
... corona más alta) que aquéllos del Mustersense típico. Este último intervalo guarda una estrecha relación con la fauna de Tinguiririca de la región central de Chile, siendo ambos actualmente considerados parte de la SALMA Tinguiririquense (Oligoceno Inferior; véase Wyss et al., 1993Wyss et al., , 1994Flynn y Wyss, 1999;Reguero, 1999;Flynn et al., 2003). ...
The fossil remains of the mammal deposit known as the "Gran Hondonada" (Sarmiento Fm., Mustersan "land-mammal age") were found in sediments of fluvial channels, disjointed, without transport evidence, and chaotically deposited. The taphonomic study was made on 1539 remains, 65% of which were determined. Most of the fossil remains correspond to Isotemnidae (Periphragnis and Ryphodon) and Archaeohyracidae (Pseudhyrax) Notoungulata. The calculated total minimum number of individuals (MNI) was 256, most of them assigned to young adults and adults. The fossil remains do not present evidences of long aerial exposition during the first biostratinomic stage. This fact allowed excellent preservation conditions. Before the incorporation of the skeletons to the fluvial channel, they would have remained in areas closer to the channel until their disarticulation. The geometric study of the bones shows a selection toward cylindrical and spherical forms, but without abrasion marks. On the basis of the taphonomic data, we can conclude that there was a relation of coexistence among fossil associations. This relation yields an autochthonous fossil deposit with transport from closer areas, and without the bones leaving their production area. Also, there exist strong evidences (i.e., non selective mortality; a high MNI; and a high sedimentation rate) to conclude that this fossil accumulation was due to a catastrophic event, occurred during a short time interval.
... The only "didelphimorph" recovered there belongs to the Herpetotheriidae, a clade with dental features that resemble Derorhynchidae (Hooker et al., 2008). Previous claims of the presence of a didelphimorphian, Pascualdelphys fierroensis from latest Eoceneearly Oligocene deposits in Tinguiririca, central Chile (Flynn and Wyss, 1999) have been recently challenged. According to Goin et al. (in press), Pascualdelphys is a junior synonym of Hondonadia (Polydolopimorphia, Bonapartheriiformes). Finally, the discovery of very diverse, successive faunas from early Oligocene deposits in La Cancha and La Cantera localities at Gran Barranca, central Patagonia (Goin et al., in press) produced no didelphoid taxa at all. ...
A new specimen of a sparassocynid didelphoid, consisting of a single skull, is described and analyzed. The specimen comes from the middle section of the Aisol Formation cropping out in Mendoza Province (Argentina) and constitutes the first marsupial hitherto described for the unit. The entire Aisol Formation was originally regarded as middle Miocene based on the fossil content. The discovery of new specimens, however, suggests that the stratigraphic level where the marsupial was found may have been deposited during the late Miocene (not older than Huayquerian times). The specimen studied here is identified as belonging to a new genus, Hesperocynus, of the family Sparassocynidae, Didelphoidea. A new combination is proposed for the already known species, H. dolgopolae (Reig 1958), previously recognized as a species of Thylatheridium Reig 1952. The new specimen from the Aisol Formation is assigned to the hypodigm of this taxon. The genus Hesperocynus encompasses small-sized carnivorous feeders as evidenced by their dental specializations and palate morphology; however, this taxon is more generalized than species of Sparassocynus, the other genus of the family. Sparassocynids have traditionally been considered the closest relatives of living didelphids. If this hypothesis is correct, then the sparassocynid clade has a long ghost lineage that covers at least 10 million years (as evidenced by the oldest known sparassocynid and didelphid remains). Sparassocynids and other didelphoids probably radiated after the global cooling event that occurred after the Eocene-Oligocene boundary.
... Si bien es cierto que entre los marsupiales sudamericanos existen casos de pérdida del m4, estos son muy contados, ocurriendo sólo entre los Polydolopimorphia: los polidolópidos Polidolopinae (Marshall, 1982b), el prepidolópido Punadolops (Goin et al., 1998) y los argirolagoideos Klohnia (Flynn y Wyss, 1999) y Patagonia (Pascual y Carlini, 1987). Por el contrario, la pérdida de al menos un premolar en la fórmula postcanina de los Eutheria es común a muchos grupos. ...
Introducción Desde mediados de la década de 1990 un equipo integrado por investigadores de la Duke University, el Museo de La Plata, el Museo Argentino de Ciencias Naturales y la Universidad de Buenos Aires ha venido realizando excavaciones sistemáticas en niveles correspondientes a la transición Paleógeno-Neógeno en la Patagonia central argentina. Los tra-bajos han cubierto aspectos estratigráficos, sedimen-tológicos, geocronológicos y paleontológicos en una escala nunca antes abordada, lo que ha permitido, entre otros aspectos, la recuperación de miles de res-tos fósiles de vertebrados. Es así que los hallazgos de mamíferos colhuehuapenses (Mioceno Temprano; Edad-mamífero Colhuehuapense), llevados a cabo en sucesivas campañas a lo largo de la pasada déca-da, han permitido aumentar significativamente AMEGHINIANA (Rev.
... Estos elementos han servido de base para sustentar la inclusión de la Superfamilia Argyrolagoidea dentro del Orden Polydolopimorphia, Suborden Bonapartheriiformes (Goin et al., 2010), que es la hipótesis de relación más robusta aceptada en la actualidad y es la seguida en este trabajo. El concepto de Argyrolagoidea utilizado es el que incluye a las familias Argirolagidae, Groeberidae, Patagonidae y a los taxones más generalizados: Praedens Goin, Abello y Chornogubsky, 2010, Klohnia Flynn y Wyss, 1999, y Epiklohnia Goin, Abello y Chornogusbky, 2010. Las convergencias postuladas entre argirolágidos y roedores resultan de importancia en las inferencias sobre el rol ecológico de este grupo de marsupiales, al tiempo que sugieren características paleoambientales determinadas. ...
... The two rodent species are noteworthy in being the earliest recorded members of that clade in South America (Flynn et al., 2003; Wyss et al., 1994; Croft et al., 2008; Flynn and Wyss, 1998). Approximately half of the species from this locality have been described in detail (Flynn and Wyss, 1999; Hitz et al., 2000; Croft et al., 2003a; Reguero et al., 2003; McKenna et al., 2006; Carlini et al., in review); current systematic efforts focus on the fauna's four notohippids, including two hypsodont (high crowned) and two brachydont (low crowned) forms (Wyss et al., 2005). The Tinguiririca Fauna differs dramatically from geologically older South American faunas in its high proportion of hypsodont mammals; such a transition does not occur on other continents until 10-15 million years later ( Flynn and Wyss, 1998). ...
The physiognomy of Chile is dominated by the Andes, the longest terrestrial mountain chain on Earth. In hindsight, given the vast exposures of stratified rocks across the range, it is remarkable that the rich fossil record of mammals in Chile remained virtually unrecognized until about 20 years ago. Our ongoing US-Chilean collaboration continues to dramatically correct this oversight, the record of Tertiary mammals now known from Chile being among the best in South America. In total we have recovered more than 2,300 specimens from some two dozen localities, spanning some 30 degrees of latitude and ranging in age from approximately 10 to 40 million years (late Eocene through late Miocene, Casamayoran through ?Chasicoan South American Land Mammal "Ages" - SALMAs; Fig. 1). Most of these specimens have been recovered from volcaniclastic sediments of the Abanico (= Coya-Machalí) Formation that were deposited as distal ignimbrites or debris flows. Because of this unusual mode of preservation, these fossils are generally exceptionally well-preserved in terms of completeness and anatomical detail. We here provide an overview our fieldwork, highlighting some of our most significant past and ongoing investigations. Late Eocene (Casamayoran and Mustersan SALMAs)
... The fauna from the stratotype sequence, discovered less than 20 years ago, is a composite section within the Abanico (=Coya-Machalí) Formation near Termas del Flaco, in the upper Tinguiririca River valley that includes some 25 mammalian taxa. Notable occurrences include: the oldest rodents from the continent (Wyss et al. 1993); two interatheres, including the earliest member of the Interatheriinae (Hitz et al. 2000); the youngest polydolopid marsupial (Flynn & Wyss 1999); the nearest recognised outgroup of the Tardigrada (McKenna et al. 2006); and the most diverse assemblage of archaeohyracids yet recorded Reguero et al. 2003). Additional taxa characterising the Tinguirirican SALMA (Wyss et al. 1994;Bond et al. 1996a, b;Hitz et al. 2000;Croft et al. 2003;Reguero et al. 2003) occur at various Argentine localities, important among them Cañadón Blanco (Roth 1901(Roth , 1903) and Ameghino's 'Partie supérieure des couchesà Astraponotus' at the Gran Barranca (Ameghino 1901a(Ameghino , 1902a -also termed the 'Astraponotéen plus supérieure' (APS; Bond et al. 1996aBond et al. , b, 1997) -the dasypodids from which are detailed below. ...
The record of Palaeogene cingulate xenarthrans in low latitudes is very poor. The cingulate fauna from the Yurúa River near Santa Rosa in eastern Perú is important because it is one of the oldest known from the Palaeogene of Perú and because of its tropical latitudinal position. Although remains are scarce, we recognize three new taxa: two species of Astegotheriini (Dasypodidae); Parastegosimpsonia peruana gen. et sp. nov., of small size, related to Eocene species from Patagonia; and another new species, ?Parastegosimpsonia sp. nov., which consists of an incomplete osteoderm representing the largest species of this tribe. A third species, Yuruatherium tropicalis gen. et sp. nov., of indeterminate suprageneric rank, shares features with Machlydotherium Ameghino (Casamayoran-Tinguirirican SALMA – middle Eocene-early Oligocene of Patagonia) and is similar to Eocoleophorus Oliveira et al. (Deseadan SALMA – late Oligocene of Brazil). We assign ?Machlydotherium intortum Ameghino (from the late Eocene of Patagonia) to Yuruatherium. Sediments bearing these cingulates also yielded rodents, marsupials and notoungulates, among the most frequent mammals. The absolute age of the sediments is unknown but an estimated age is inferred from studies of the mammalian assemblages. The age of the Santa Rosa local fauna is still controversial and given the groups taken into account, could be from Early Eocene to Late Oligocene. According to sequences of southern cingulate faunas (especially those of Dasypodidae), the cingulates from Santa Rosa also suggest an age between the Late Eocene and Early Oligocene. Nevertheless, the very low latitude of the Santa Rosa local fauna should be taken into account because in lower latitudes it is not uncommon to find taxa with a more generalized set of characters than those present in contemporary taxa from higher latitudes.
... A second source of arguments is whether this family was part of the Paucituberculatan radiation (caenolestids and allies) or not. These and other aspects of argyrolagid diversity and affinities are the subject of ongoing discussions (SIMPSON 1970a;HOFFSTETTER & VILLARROEL 1974;MARSHALL 1980MARSHALL , 1982MARSHALL , 1987WOLFF 1984;CARLINI & PASCUAL 1985;PASCUAL & CARLINI 1987;MARSHALL et al. 1990;SÁNCHEZ-VILLAGRA & KAY 1997;FLYNN & WYSS 1999;SÁNCHEZ-VILLAGRA et al. 2000;WYSS et al. 1994;SÁNCHEZ-VILLAGRA 2001;GOIN 2003;GOIN & CANDELA 2004. Here we report a new genus and species of Argyrolagidae, recognized on the basis of several cranial, mandibular, and dental specimens recovered from strata of Early Miocene age of Central Patagonia. ...
We describe Anargyrolagus primus gen. et sp. nov. (Marsupialia, Polydolopimorphia, Bonapartheriiformes, Argyrolagoidea), represented by cranial and mandibular remains collected from Colhuehuapian beds (Early Miocene) of Patagonia (Chubut Province, Argentina). This species is the oldest and most primitive argyrolagid known from Patagonia. In several aspects it resembles the cranial, mandibular, and dental features exhibited by the late Miocene species of Argyrolagus; however, it preserves three additional teeth of the generalized metatherian dental formula, the canine and the first two premolars. In occlusal view, its molars are more quadrangular in outline than those of Argyrolagus and Microtragulus.
The current literature on marsupial phylogenetics includes numerous studies based on analyses of morphological data with limited sampling of Recent and fossil taxa, and many studies based on analyses of molecular data with dense sampling of Recent taxa, but few studies have combined both data types. Another dichotomy in the marsupial phylogenetic literature is between studies focused on New World taxa and those focused on Sahulian taxa. To date, there has been no attempt to assess the phylogenetic relationships of the global marsupial fauna based on combined analyses of morphology and molecular sequences for a dense sampling of Recent and fossil taxa. For this report, we compiled morphological and molecular data from an unprecedented number of Recent and fossil marsupials. Our morphological data consist of 180 craniodental characters that we scored for 97 terminals representing every currently recognized Recent genus, 42 additional ingroup (crown-clade marsupial) terminals represented by well-preserved fossils, and 5 outgroups (nonmarsupial metatherians). Our molecular data comprise 24.5 kb of DNA sequences from whole-mitochondrial genomes and six nuclear loci (APOB, BRCA1, GHR, RAG1, RBP3 and VWF) for 97 marsupial terminals (the same Recent taxa scored for craniodental morphology) and several placental and monotreme outgroups. The results of separate and combined analyses of these data using a wide range of phylogenetic methods support many currently accepted hypotheses of ingroup (marsupial) relationships, but they also underscore the difficulty of placing fossils with key missing data (e.g., Evolestes), and the unique difficulty of placing others that exhibit mosaics of plesiomorphic and autapomorphic traits (e.g., Yalkaparidon). Unique contributions of our study are (1) critical discussions and illustrations of marsupial craniodental morphology including features never previously coded for phylogenetic analysis; (2) critical assessments of relative support for many suprageneric clades; (3) estimates of divergence times derived from tip-and-node dating based on uniquely taxon-dense analyses; and (4) a revised, higher-order classification of marsupials accompanied by lists of supporting craniodental synapomorphies. Far from the last word on these topics, this report lays the foundation for future research that may be enabled by the discovery of new fossil taxa, better-preserved material of previously described taxa, novel morphological characters (e.g., from the postcranium), and improved methods of phylogenetic analysis.
The enigmatic Gondwanatheria includes mammals with a mosaic of plesiomorphic and apomorphic cranial and dental features challenging our attempts to reconstruct their phylogenetic affiliation. They are generally perceived as sharing a closer ancestor with multituberculates than with therians in a variably conceived Allotheria. Two major groups are classically recognized among the South American Gondwanatheria: the brachyodont-toothed Ferugliotheriidae and the hypsodont-toothed Sudamericidae, although not all taxa fall easily in these categories. The affinities of the Ferugliotheriidae are, however, unsettled, with some authors favoring the hypothesis that they are indeed a derived branch of multituberculates. The original foundational Patagonian finds of gondwanatherians have recently been much improved by spectacular Late Cretaceous Malagasy materials, which increase dental diversity of the group, provide detailed cranial/postcranial morphology, and support allotherian affinities for the group.
Marsupials and other metatherians apparently arrived in South America before the beginning of the Paleogene, at the end of the Cretaceous. The earliest relatives of Australian marsupials, the Microbiotheria, appear in the earliest assemblage. The carnivorous sparassodonts evolved the largest metatherian predators known, such as the 600 kg Proborhyaena, as well as the jaguar-sized saber-toothed marsupial Thylacosmilus. Many of these poorly known marsupial predators are well-illustrated by Roman Uchytel.
Los hallazgos realizados en las dos y media últimas décadas de numerosas localidades a lo largo del territorio chileno con abundantes y variados restos fósiles de mamíferos terrestres cenozoicos, pre-pelistocénicos, han constituido una revolución para el conocimiento de la fauna sudamericana en esta región andina. La fauna recuperada cubre un rango de edad de, al menos, 30 millones de años (entre ~40 y ~10 millones de años atrás) y un rango latitudinal cercano a 30º (entre el Altiplano y la Patagonia) y constituye uno de los más completos e importantes archivos de la evolución de los mamíferos en el continente. Estos hallazgos han tenido importantes implicancias para establecer con bastante precisión comprender la historia evolutiva de los mamíferos sudamericanos y la evolución geológica (tectónica América del Sur y la escasez de estudios anteriores en territorio chileno, la mayor parte de las formas fósiles encontradas corresponden a especies nuevas para la ciencia. La importancia que revisten estos hallazgos se hace más palpable aún si se considera que hasta mediados del siglo pasado sólo se tenía conocimiento en el país de un solo sitio con mamíferos fósiles terciarios, cual es el río Frías (río Cisnes), en Aysén. Las regiones fosilíferas corresponden, de Norte a Sur, a: 1. Precordillera de Arica-Iquique (localidad de Caragua), 2. Cordillera Occidental de Arica-Iquique (localidad de Chucal), 3. Franja costera de la región de Caldera, 4. Cordillera Principal de Chile central (entre las hoyas superiores de los ríos Maipo y Bio-Bío), 5. Sector del río Cisnes (o Frías), Región de Aysén, 6. Meseta Guadal-Cosmelli, Región de Aysén, y 7. Región de Magallanes, en diversos sectores. Los estratos fosilíferos de cada una de estas regiones y localidades, a excepción de Bahía Inglesa, que corresponde a un ambiente litoral, se depositaron en cuencas formadas en ambientes terrestres, localmente con desarrollo de lagos y asociadas con actividad volcánica. Estas cuencas estuvieron controladas por la actividad de fallas (en en ambientes geológicos tectónicamente activos, pero de naturaleza diferente. En este estudio se hace especial énfasis en las regiones 1, 2 y 4, mencionadas, donde las investigaciones interdisciplinarias estos ambientes. Se enumeran las formas fósiles recolectadas y se destaca sus implicancias geológicas, evolutivas y paleoambientales.
Por décadas, el registro fósil de vertebrados en Chile fue exiguo, restringido a pocos hallazgos, muchos de ellos fortuitos. En contraposición a esta situación, grandes figuras de la ciencia, entre ellos Charles Darwin, Rudolph Philippi y Claude Gay, entre otros, notaron tempranamente el valor de este registro, a la vez que dieron a conocer desde el siglo XIX restos de vertebrados fósiles hallados en este exótico rincón llamado Chile. Esto no es una mera coincidencia, dado que a través de la historia geológica de nuestro planeta, Chile ha sido en forma relativamente persistente, el territorio que conformó el margen suroccidental de Pangea, luego de Gondwana, y finalmente de Sudamérica. Debido a esto, los depósitos sedimentarios que se encuentran en el país albergan evidencia fundamental para comprender la evolución de las biotas de vertebrados marinos del antiguo Panthalassa y posteriormente del Océano Pacífico. Esta evidencia es de alta relevancia para comprender los cambios experimentados por dicha fauna en este margen del planeta a través del tiempo, considerando que América del Sur fue antiguamente parte de un mega-continente, posteriormente una isla, y finalmente una gran masa escasamente conectada con Norteamérica a través un puente continental. A lo anterior se suma el “reciente” alzamiento de la Cordillera de Los Andes y la conformación de desiertos durante el Pleistoceno, lo que ha ocasionado que nuestra actual fauna de vertebrados sea bastante divergente de las formas que antiguamente habitaron Chile.
En este sentido, la presente publicación busca entregar al lector un acercamiento sintético sobre las formas de vertebrados que habitaron nuestro país durante su pasado geológico, mostrando una fauna muchas veces insospechada, la que existió en los mismos lugares comunes en donde hoy habitamos, y cuya real diversidad comienza a develarse paulatinamente en la medida que prosiguen las investigaciones sobre vertebrados fósiles. Esta publicación es una revisión general de los principales grupos animales que conforman el patrimonio paleontológico de vertebrados a nivel nacional. Cada capítulo fue realizado por especialistas nacionales e internacionales en los diferentes grupos taxonómicos en los que fue dividido este libro, y elaborado de manera tal que permita un fácil entendimiento de la distribución geográfica, temporal, y los taxa representados para cada uno de los grupos tratados.
Para algunos lectores el resultado de esta compilación será un poco asimétrica debido a que no todos los grupos tienen, por ahora, una gran representatividad en el registro fósil en Chile o, en otros, no se cuenta con todos los especialistas específicos de ciertos taxa, lo que se traduce en pocos datos sobre estos grupos animales. Es precisamente por estos ‘vacíos’ de información que la continuidad de las investigaciones sobre los vertebrados fósiles de Chile es de alta importancia.
Resulta interesante generar una retrospectiva. Desde los años 60-70’s, cuando el destacado paleontólogo argentino Rodolfo Casamiquela realizó una serie de importantes contribuciones, que no se vivía un repunte en la paleontología de vertebrados, no sólo en publicaciones, sino además, de investigadores chilenos y residentes en Chile. La investigación paleontológica en Chile se había centrado fundamentalmente en estudios estratigráficos y paleoambientales, que prefieren el estudio de fósiles numerosos, pequeños, y fáciles de recolectar, como los microfósiles (foraminíferos, palinomorfos), plantas, e invertebrados. Esto incluso llevó a una especie de mito implícito en la cultura nacional, de que “los vertebrados no sirven”. Sin embargo, no por ser más difíciles de recolectar y/o identificar, los restos de vertebrados son menos informativos para estas materias, como queda bien establecido en el presente libro. Actualmente, se ha generado una escuela de investigadores en Chile con los conocimientos de morfología y sistemática de vertebrados fósiles necesarios para determinarlos, estudiarlos, y reconocer sus implicaciones para éstas y otras áreas, incluyendo morfología, paleobiología, y evolución. Hace un par de décadas, estudiar los vertebrados fósiles siempre requería de colaboraciones con investigadores residentes en el extranjero. Otra notable diferencia está dada por el contundente impacto social que han significado los vertebrados fósiles en términos patrimoniales, museográficos, y mediáticos, un desarrollo notable que promete un “nuevo trato” para la paleontología en Chile.
Debido a que el conocimiento de los vertebrados fósiles de Chile sigue creciendo vertiginosamente, es que creemos que este proyecto no se detendrá aquí y nos veremos ciertamente en la necesidad de ir
actualizando este registro de manera de ir entregando, a la comunidad científica e interesados no académicos, datos actualizados de la historia paleontológica de Chile.
Por ahora el libro incluye el registro fósiles de peces divididos en cartilaginosos y óseos; tetrápodos basales y anfibios; reptiles, estos divididos en ictiosaurios, tortugas, plesiosaurios y arcosaurios no avianos (decidimos dejar las aves como grupos separado para facilitar la lectura); y mamíferos fósiles abordando su registro pre-Pleistocénico, Pleistocénico y mamíferos marinos agrupados en cetáceos y no cetáceos.
Llevar a cabo este trabajo no fue fácil. Aquí se reúnen décadas de investigaciones a cargo de diferentes actores del quehacer paleontológico nacional, investigaciones que gracias a la buena voluntad y colaboración de cada una de las personas involucradas, ha quedado finalmente plasmado en cada respectivo capítulo de este libro. Este minucioso trabajo de recopilación de parte de todos los especialistas ha sido finalmente aunado en la compilación de este material.
Agradecemos al Director del Museo Nacional de Historia Natural, Sr. Claudio Gómez y a la ex curadora Jefe de la misma institución, Rocío Jaña por el apoyo brindado para publicar este documento a través de la publicación ocasional del museo. Agradecemos especialmente el Editor de las publicaciones científicas del Museo Nacional de Historia Natural, Herman Núñez por su inagotable entusiasmo, apoyo y profesionalismo al trabajar en la edición general de esta publicación. También queremos extender nuestros más sinceros agradecimientos al paleontólogo Sergio Soto Acuña quien desinteresadamente apoyo el trabajo editorial y revisó minuciosamente diferentes capítulos del libro.
Esperamos que este volumen sea un estímulo para la continuación de las investigaciones sobre paleontología de vertebrados en Chile, e inspire a nuevas generaciones de profesionales a dedicarse a la paleontología de vertebrados y, en especial, a crear y conducir líneas de investigación de las que se obtenga información de grupos menos representados para conocer con más detalle la historia natural de Chile.
This final chapter is designed primarily for the foreign visitor to Chile who wishes to gain a broad overview of the field geology and scenery of central and northern Chile. We hope that it will also aid an appreciation of the nature of human interaction with this climatically and topographically challenging area, from the early settlers to the modern mining industry. This is a traverse along and across one of the world's classic compressional ocean-continent subduction zones, where strong coupling between the oceanic and continental plates is linked to active mountain building, dramatic scenery, and frequent earthquake and volcanic activity. The drive moves north from Santiago, which lies in the forearc Central Valley west of the South American Southern Volcanic Zone, into one of the flat-slab Andean segments. Within this flat-slab zone we divert east to describe a west-to-east across-strike traverse from the coast into the High Andes where, because of the low dip of the subducting plate, volcanoes are absent (Chapters 4 and 5). Returning to the coast, the drive continues north into the latitude of the South American Central Volcanic Zone, with its superbly developed line of modern volcanoes in the hyperarid high Atacama Desert. A second west-to-east traverse from the coast to these volcanoes illustrates how the modem continental forearc region is segmented into a series of mountain belts and intervening basins, each with its own distinctive scenery and geology. Additional details on the rock units and places visited, and the tectonic settings of ancient and modem Chile, can be found by researching the previous chapters. The route described runs from Zapallar, with its mediterranean climate on the coast north of Santiago, to San Pedro de Atacama, which lies deep in the desert close to the Bolivian border (Figs 13.1 & 13.2). A northern route has been chosen primarily because, given the dry climate, rock exposure is better and the spectacular landscapes of the Atacama Desert are a likely highlight of any visit to Chile. Those with additional time could head south to enjoy the dramatic geomorphology of the Central Valley and southern Andean volcanoes, as well as examine excellent coastal exposures such as the accretionary complex exposed south of Pichulemu, but anyone undertaking fieldwork in southern Chile must deal with thick vegetation and a damp climate.
WEAR PATTERN AND OCCLUSION IN THE MASTICATORY SYSTEM OF EXTINCT ARGYROLAGOIDEA (MARSUPIALIA, POLYDOLOPIMORPHIA, BONAPARTHERIIFORMES). The Argyrolagoidea (Mammalia, Marsupialia, Polydolopimorphia, Bonapartheriiformes) display a pattern of cusp contact that is quite different from any other group of South American metatherians during dental occlusion. The resulting pattern of wear facets is also exclusive for this group. In part, this is due to the highly derived molar morphology of argyrolagoids as compared to the generalized tribosphenic pattern. The location and relative development of wear facets indicate that chewing movements were composed of propalinal and ectental components, resulting in an oblique motion. This type of masticatory dynamics correlates with the argyrolagoid molar pattern, including a reorganization of cusps and the addition of neomorphic structures. This pattern of molar wear, the occlusal movements, and the acquisition of hypsodonty strongly support the hypothesis of an herbivorous diet for this group. The occurrence of hypsodonty in South American metatherians already by the early Oligocene appears to be a remarkably rapid response to environmental changes. Body mass estimates are consistent with those of many small herbivores (i.e., rodents).
WEAR PATTERN AND OCCLUSION IN THE MASTICATORY SYSTEM OF EXTINCT ARGYROLAGOIDEA (MARSUPIALIA, POLYDOLOPIMORPHIA, BONAPARTHERIIFORMES). The Argyrolagoidea (Mammalia, Marsupialia, Polydolopimorphia, Bonapartheriiformes) display a pattern of cusp contact that is quite different from any other group of South American metatherians during dental occlusion. The resulting pattern of wear facets is also exclusive for this group. In part, this is due to the highly derived molar morphology of argyrolagoids as compared to the generalized tribosphenic pattern. The location and relative development of wear facets indicate that chewing movements were composed of propalinal and ectental components, resulting in an oblique motion. This type of masticatory dynamics correlates with the argyrolagoid molar pattern, including a reorganization of cusps and the addition of neomorphic structures. This pattern of molar wear, the occlusal movements, and the acquisition of hypsodonty strongly support the hypothesis of an herbivorous diet for this group. The occurrence of hypsodonty in South American metatherians already by the early Oligocene appears to be a remarkably rapid response to environmental changes. Body mass estimates are consistent with those of many small herbivores (i.e., rodents).
More than 10,000 years ago spectacularly large mammals roamed the pampas and jungles of South America. This book tells the story of these great beasts during and just after the Pleistocene, the geological epoch marked by the great ice ages. Megafauna describes the history and way of life of these animals, their comings and goings, and what befell them at the beginning of the modern era and the arrival of humans. It places these giants within the context of the other mammals then alive, describing their paleobiology--how they walked; how much they weighed; their diets, behavior, biomechanics; and the interactions among them and with their environment. It also tells the stories of the scientists who contributed to our discovery and knowledge of these transcendent creatures and the environment they inhabited.
South America was isolated from other continents during most of the Cenozoic, developing a singular mammalian fauna. In contrast to North America, Europe, Asia, and Africa, up to the late Neogene, the carnivore adaptive zone in South America was populated by crocodiles (Sebecidae), large snakes (Madtsoiidae), large birds (Phorusrhacidae), and metatherian mammals (Sparassodonta). Sparassodonta were varied and comprised a wide range of body masses (≈ 2–50 kg) and food habits. Their diversity decreased towards the late Miocene (Huayquerian Stage/Age) and the group became extinct in the “middle” Pliocene (≈ 3 Ma, Chapadmalalan Stage/Age). Several authors have suggested that the cause of this decline and extinction was the ingression of carnivorans to South America (about 6–7 Ma ago), because they competed with the Sparassodonta; although this hypothesis has been criticized in recent years. With the intention of testing the hypothesis of “competitive displacement,” we review the fossil record of South American Sparassodonta and Carnivora, collect data about diversity, estimate size and diet, and determine first and last appearances. The diversity of Sparassodonta is low relative to that of Carnivora throughout the Cenozoic with the early Miocene (Santacrucian Stage/Age) showing the greatest diversity with 11 species. In the late Miocene-middle Pliocene (Huayquerian Stage/Age), the fossil record shows overlap of groups, and the Sparassodonta’s richness curve begins to decline with the first record of Carnivora. Despite this overlap, carnivorans diversity ranged from four or fewer species in the late Miocene-Pliocene to a peak of around 20 species in the early Pleistocene (Ensenadan Stage/Age). Carnivora was initially represented by small-sized, omnivorous species, with large omnivores first appearing in the Chapadmalalan Stage/Age. Over this period, Sparassodonta was represented by large and small hypercarnivores and a single large omnivorous species. From this review of the fossil record, it is suggested that factors other than competitive displacement may have caused the extinction of the Sparassodonta.
We provide the first detailed description of the oste-ology of the enigmatic Oligo-Miocene Australian metatherian Yalkaparidon. This taxon exhibits a number of unusual craniodental apomorphies but appears to be plesiomorphic with-in Metatheria in retaining four molars, rather than three as previously reported. We demonstrate that the only known skull of Yalkaparidon almost certainly represents a single individual. We also tentatively refer a number of isolated tarsals to the genus. Maximum parsimony analyses of a 258 character mor-phological matrix (with information from the tarsals described here either included or excluded) place Yalkaparidon within the superordinal clade Australidelphia, but Bayesian analyses of the same matrix are less well resolved, placing Yalkaparidon within Marsupialia but without unequivocally supporting austra-lidelphian affinities. Bayesian analyses of a total evidence matrix that combines the morphological data with 9 kb of sequence data from five nuclear protein-coding genes (APOB, BRCA1, IRBP, RAG1 and VWF), 78 indels, and 53 retroposon insertion characters are similarly poorly resolved and do not clarify the supraordinal relationships of Yalkaparidon beyond suggesting that it is probably a member of Marsupialia. However, if the tarsal remains are correctly attributed to Yalkaparidon, then membership of Australidelphia seems likely, as these specimens exhibit characteristic australidelphian apomorphies. We con-clude that the ordinal status of Yalkaparidon remains justified based on current evidence, and we present a revised diagnosis for Yalkaparidontia. We maintain the two currently recognized species, Y. coheni and Y. jonesi, but present revised specific diagnoses. We suggest a revised phylogenetic definition for Marsupialia, and provide phylogenetic definitions for Eomarsupialia (the clade comprising all extant Australian mar-supial orders) and for the clade comprising Dasyuromorphia, Peramelemorphia, and Notoryctemorphia to the exclusion of Diprotodontia; we propose the name Agreodontia for the latter clade.
We describe small-bodied archaeohyracids of transitional Eocene-Oligocene age from Chubut, Argentina, including two from Santiago Roth’s important but poorly known Cañadón Blanco locality and two occurring in the Tinguiririca Fauna of the Andean Main Range of central Chile. Three taxa are recognized. We refer specimens from both Patagonia and the central Andes to one of these taxa, initially named Archaeohyrax gracilis by Roth (1903) but receiving
a new generic designation here. A diminutive form from Can˜ado´n Blanco and an intermediate-sized form from Chile are each recognized as new species. These taxa help to clarify the temporal correlation of lithostratigraphic units currently located on opposite sides of the Andean divide, and aid in the recognition of a biochronologic interval, the early Oligocene (to possibly late Eocene)-aged Tinguirirican, interposed between the classical Mustersan and Deseadan ‘‘ages’’ of the South American land mammal succession.
The Abanico (= Coya-Machalí) Formation of the Chilean Andes Cordillera continues to yield beautifully preserved fossil mammals of a variety of Cenozoic ages, with previously documented faunas spanning at least the Eocene to early Miocene. We describe here a new species of polydolopine marsupial, Polydolops mckennai, based on a skull preserving most of the upper dentition or alveoli. This, only the second polydolopid cranium known, provides important information on dental homologies and phylogeny for the group. The specimen on which this taxon is based is the first reported from new localities in the Río Cachapoal drainage. These localities appear to be early Oligocegrave;ne or older in age (at least in part), expanding the geographic and temporal distribution of mammalian faunas from the Abanico Formation and bearing on models of the tectonic evolution of the central Chilean Andes.
To discover interordinal relationships of living and fossil placental mammals and the time of origin of placentals relative
to the Cretaceous-Paleogene (K-Pg) boundary, we scored 4541 phenomic characters de novo for 86 fossil and living species.
Combining these data with molecular sequences, we obtained a phylogenetic tree that, when calibrated with fossils, shows that
crown clade Placentalia and placental orders originated after the K-Pg boundary. Many nodes discovered using molecular data
are upheld, but phenomic signals overturn molecular signals to show Sundatheria (Dermoptera + Scandentia) as the sister taxon
of Primates, a close link between Proboscidea (elephants) and Sirenia (sea cows), and the monophyly of echolocating Chiroptera
(bats). Our tree suggests that Placentalia first split into Xenarthra and Epitheria; extinct New World species are the oldest
members of Afrotheria.
A skull of the oldest described argyrolagid, Proargyrolagus bolivianus (late Oligocene of the Salla Beds, Bolivia) allows an assessment of the phylogeny of this group and a reconstruction of its paleobiology. Several aspects of the cranial anatomy of the Monodelphis-sized Proargyrolagus serve to support the hypothesis that argyrolagids are marsupials: the palate has large vacuities, the angular process is medially inflected, the auditory bulla is composed of a wing of the alisphenoid, and the dental formula includes four molars. Like Argentine Plio-Pleistocene argyrolagids, Proargyrolagus has an unfused symphysis, and a phaneric and almost vertically oriented ectotympanic in the shape of a flattened ring. Proargyrolagus is more primitive in having a less globular braincase, smaller orbits, and a shallower mandible. The dental formula is 4/3.1/1.3/2.4/4 or 4/4.1/0.3/2.4/4 (vs. 2/2.0/0.1/1.4/4 for Argyrolagus). Large infraorbital foramina transmitted nerves and vessels of the snout. The snout is long with the nasals projecting well forward of the incisors and with a strong antorbital fossa for facial muscles. It can be inferred that this animal had well-developed vibrissae and a mobile proboscis, and relied heavily on its rostrum to gather tactile information. Food manipulation was assisted by an elongate, procumbent lower incisor that occluded with three sharply-edged upper incisors, as in living phalangeriform marsupials. Like Plio-Pleistocene argyrolagids and extant elephant shrews, Proargyrolagus has prismatic and high crowned cheek teeth suggesting an abrasive diet consisting perhaps of seeds.
We report here on newly collected materials comprising the best known remains of the extinct South American mammal Groeberia minoprioi. Comparison with the holotype of this species and that of Groeberia pattersoni, all of which are from the same Divisaderan (late Eocene or early Oligocene) locality and level, provides the following new conclusions: (1) A pair of elongated palatal vacuities, the cheektooth formula, and the macropodoid-like mandibular inflection are the most conclusive features of marsupial affinities for Groeberia. (2) The unique combination of autapomorphies present in this taxon justifies placement of the monotypic Groeberiidae in a new order, Groeberida. The most unusual of these autapomorphies is the presence of two pairs of somewhat gliriform incisors inserted in unusually developed premaxillae, together with the posterior projection of the mandibular symphysis, which forms a basal osseous floor for the co-ossified rami. This combination of features results in a skull architecture unmatched among other mammals. (3) The dental structure and inferred masticatory mechanics are suggestive of dietary preference for hard items. (4) Analysis of the depositional history of the Divisadero Largo Formation indicates marked seasonality.
EXTANT marsupials are distinctive in their pattern of dental development1, in that only one tooth is replaced postnatally in each jaw. Interpretation of this pattern for marsupials ancestrally is disputed2-5, partly because ontogenetic data in fossils have been unobtainable. Here we present an ultra-high-resolution X-ray computed tomography (CT) study of the tiny fossil Alphadon, which represents the first evidence of dental development and replacement in a Mesozoic marsupial. In the known pattern of tooth replacement and development, Alphadon is identical to living marsupials, a derived similarity suggesting that this pattern is ancestral to Marsupialia, and that it was established by the Late Cretaceous, at least. This pattern has been correlated with some specialized aspects of marsupial lactation1,6. Hence the presence of a marsupial pattern of tooth replacement in Alphadon provides indirect evidence that at least some specialized features of marsupial reproductive processes arose during the Mesozoic.
Mammalia is defined by its ancestry as the taxon originating with the most recent common ancestor of extant Monotremata and Theria. To diagnose Mammalia as so defined, 176 character transformations in the skull and postcranial skeleton, distributed among Placentalia, Marsupialia, Multituberculata, Monotremata, Morganucodontidae, Tritylodontidae, and Exaeretodon, were polarized, scored, and subjected to PAUP. Only one most parsimonious tree was identified (BL = 190, CI = 0.926): (Exaeretodon (Tritylodontidae (Morganucodontidae (Monotremata (Multituberculata (Marsupialia, Placentalia)))))).Thirty-seven osteological synapomorphies diagnose Mammalia. Triassic and Early Jurassic taxa commonly referred to as mammals, including Morganucodontidae, Kuehneotheriidae, and Haramiyidae, were found to lie outside of Mammalia. These fossils document that the mammalian lineage had diverged from other known synapsid lineages by the Norian (Late Triassic). However, the earliest evidence that Monotremata and Theria had diverged from their most recent common ancestor, and thus the earliest evidence of Mammalia itself, is of Bathonian (Middle Jurassic) age. Many of the diagnostic attributes of Mammalia are associated with either the sensory organs housed in the skull, the masticatory system, or the craniovertebral and atlas-axis articulations. Modification of each of these regions has long been tied to the origin of mammals. However, other synapomorphies are identified which suggest that additional factors must be sought to fully understand the origin of Mammalia.
We describe Rosendolops primigenium gen. et sp. nov (Mammalia, Marsupialia, Polydolopimorphia), based on isolated upper molars found in early Eocene (Casamayoran Age) beds from the cliffs south of Lake Colhue-Huapi (Province of Chubut, Argentina). The molar pattern shown by Rosendolops primigenium is clearly anticipatory of the characteristic polydolopimorphian (i.e., Prepidolopidae, Bonapartheriidae, and Polydolopidae) pattern, although the synapomorphies typical of the group are already present. Reigia punae and the Protodidelphidae (sensu Marshall, Case and Woodburne, 1990) are excluded from the Polydolopimorphia as they lack these synapomorphies. The morphotype represented by Rosendolops primigenium sheds new light on the possible progressive modifications that enabled the establishment of the molar pattern in South American “pseudodiprotodont” marsupials.
THE distinctive soft anatomy and reproductive biology of marsupials sets them apart as a unique group within mammals. These features are, of course, absent in fossils, so it is difficult to determine marsupial origins and evolution: many of the proposed dental and skeletal characters are controversial1 or primitive1,2. A contribution of the alisphenoid bone to the tympanic bulla of the skull has long been considered a reliable diagnostic feature of the group1–5. But this feature is lacking both in the borhyaenoid marsupial Mayulestes ferox, which I describe here, and the didelphoid Pucadelphys andinus
6,7, both from the early Palaeocene of Bolivia7–9. Comparison with younger taxa suggests that this feature appeared several times independently within the group, and is thus an inappropriate defining character. What, then, is a marsupial?
Middle Eocene land mammals from La Meseta Formation, Seymour (Marambio) Island are reviewed. A taxonomically diverse fossil land-vertebrate assemblage with small and medium-size mammals has been recovered from four localities. The depositional setting is shallow marine and most of the mammal-bearing beds are in reworked, moderate to high energy subtidal facies. The characteristics of these mammals not only confirm but also strengthen the biogeographical relationships between southern South America (Patagonian Province) and the Antarctic Peninsula during the Paleogene and rule out the possibility of a major barrier between these areas. The Antarctic ungulates (Astrapotheria and ?Litopterna) are plesiomorphics in retaining low crowned cheek teeth and are more similar to those from the Pancasamayoran local faunas of southern South America (Patagonia).
We add to the knowledge of the dentition and lower jaw of the primitive marsupial or near marsupial, Kokopellia juddi, based on newly collected materials from the medial Cretaceous (Albian–Cenomanian) of central Utah. The dental formula, i4 c1 p3 m4, is primitive for (or with respect to) Marsupialia, as are a number of features of the dentary and dentition: presence of a labial mandibular foramen, ?an inflected angle, ?and a trace of the meckelian groove; lack of staggering of the lower incisor series; lack of twinning between entoconid and hypoconulid on lower molars; incompletely lingual position of lower molar paraconid; upper molar protocone relatively small and mesiodistally narrow; and conules placed about halfway between the protocone and the paracone–metacone. Other than the stylocone, cusps are lacking from the stylar shelf; we argue that this represents the primitive marsupial condition based on the economy of character change and the stratigraphic record of marsupials in the Cretaceous of North America. Recent discoveries of early marsupials, eutherians, and therians of metatherian–eutherian grade provide data indicating that some derived features of the dentary and dentition (e.g., loss of coronoid, meckelian groove, and labial mandibular foramen; acquisition of strong, winged conules, double rank postvallum/prevallid shearing, and stylar cusp D) probably arose independently, in some cases more than once, among the major groups of tribosphenic mammals. In turn, this suggests that a common ancestor for marsupials and placentals was more primitive than has generally been appreciated.
New geologic, paleontologic and isotopic geochronometric results from the Termas del Flaco region in the upper Tinguiririca River valley in central Chile demand considerable revision of the accepted geotectonic history of the Andean Main Range in this region. A diverse, transitional Eocene-Oligocene aged, land-mammal fauna was recovered from several sites in volcaniclastic sediments of the Coya-Machalí (=Abanico) Formation. Major results of our study include: 1) The 1000 + m thick studied deposits, previously attributed to the Cretaceous Colimapu Formation, belong to the Coya-Machalí (=Abanico) Formation. Radioisotopic data from levels immediately above (31.5 Ma) and below (37.S Ma) the fossiliferous horizon indicate a latest Eocene to early Oligocene age for the basal part of the formation and the fauna contained in it. 2) The fossiliferous unit rests with slight angular offset on different Mesozoic units: “Brownish-red Clastic Unit” (BRCU) and Baños del Flaco Formation; in a limited area it also overlies a white tuff dated at 104 Ma. 3) The contacts just discussed (none of which is attributable to faulting), demonstrate the existence of two, or possibly three, unconformities in the region. 4) Sedimentological criteria argue against reference of the BRCU to the Colimapu Formation, and imply correlation of the former unit to basal levels with in the late Cretaceous Neuquén Group of western Argentina. 5) The Coya-Machalí Formation, previously viewed as representing the western volcanic equivalent of Riogrd́ndico Supercycle deposits of western Argentino, is likely coeval to much younger units in that region such as the Agua de la Piedra Formation. 6) Paleomagnetic results from the fossil producing horizon indicate about 20 ° of post-early Oligocene, counterclockwise rotation. 7) Fossil mammals from the Coya-Machalí Formation near Termas del Flaco represent a distinct biochronologic interval not heretofore clearly recognized from elsewhere on the continent. This new fauna helps fill the long recognized post-?middle Eocene, pre-late Oligocene faunal hiatus between the Mustersan and Deseadan South American Land Mammal Ages (SALMA). In addition, it records the earliest known presence of rodents in South America and otherwise differs strongly from the enigmatic Divisaderan SALMA.ResumenEstudios geológicos, paleontológicos y radioisotópicos recientes efectuados en la región de Termas del Flaco, v alle superior del no Tinguiririca, Chile central, permiten modificar considerablemente la evolución lectánica de la Cordillera Principal en esta region. Los fósiles corresponden a una variada fauna de mamíferos colectados en varias localidades y niveles de edad eocena — oligocena de la Formatión Coya-Machalí (=Abanico). Los principales resultados obtenidos son: 1) Los depósitos de esta region previamente atribuidos a la Formatión Colimapu, cretácica, pertenecen a la Formatión Coya-Machalí (=Abanico). Las dataciones radioisotópicas y indican una edad Eoceno más alto (37,5 Ma) a Oligoceno inferior (31,5 Ma) para la parte inferior de la formatión y la fauna fósil contenida en ella. 2) Los depósitos terciarios fosilíferos se apoyan con discordancia de erosión y levé angularidad sobre diferentes unidades mesozoicas: “Unidad Clástica Pardo-rojiza” (BRCU) y Formation Baños del Flaco. En un reducido sector recubren a una toba blanca datada en 104 Ma. 3) Los contactos discordantes mencionados, ninguno de los cuales es atribuible a una falla, ponen en evidencia la existencia de dos, posiblemente tres, discordancias en esta region. 4) Se excluye la pertenencia de la BRCU a la Formatión Colimapu y se la correlaciona con el Grupo Neuquén, del Cretácico Superior, conocido en la vertiente cordillerana argentina. 5) La Formación Coya-Machalí, anteriormente considerada un equivalente volcánico del Superciclo Riográndico, sería coetánea con unidades más jóvenes de Argentina como la Formación Agua de la Piedra. 6) Los estudios de paleomagnetismo en muestras de los horizontes fosilíferos indican una rotatión antihoraria post-Oligoceno inferior de unos 20 °. 7) Los restos de mamíferos fósiles encontrados representan un intervalo biocronológico bien definido, no reconocido claramente hasta la fecha en América del Sur. Esta fauna completa el hiatus post?-Eoceno medio a pre-Oligoceno superior cuya existencia se acepta entre las Edades Mamífero Mustersense y Deseadense, registra la presencia más antigua de roedores en América del Sur y se diferencia claramente de otra Edad Mamífero, el enigmático Divisaderense.
Defining the names of taxa in terms of common ancestry, that is, using phylogenetic definitions of taxon names, departs from a tradition of character-based definitions by granting the concept of evolution a central role in taxonomy. Phylogenetic definitions bear on other taxonomic principles and practices, including the following: (1) Names cannot be applied to nonmonophyletic taxa as the result of mistaken ideas about relationships or characters. Such mistakes do not affect conclusions about the monophyly of taxa but about their content and/or diagnoses. Because nonmonophyletic taxa can only be named deliberately, they are easily avoided. (2) Definitions are clearly distinguished from descriptions and diagnoses. Definitions are ontological statements about the existence of entities that result from the relationships of common ancestry among their parts; descriptions and diagnoses are epistemological statements about how we recognize the parts of those entities. (3) By precisely specifying the clade (ancestor) with which a name is associated, phylogenetic definitions clarify the limits of taxa, and this in turn clarifies related phenomena such as time of origin and duration. (4) Unlike the case for character-based intensional definitions and enumerative extensional definitions, phylogenetic definitions provide an unambiguous criterion for synonymy of taxon names: names are synonymous if they refer to clades stemming from the same ancestor. (5) Because of their relevance to synonymy, phylogenetic definitions also are relevant to priority, of both names and authorship. In phylogenetic taxonomy, priority is based not on first use of a name at a particular rank or ranJc-group but on first use of a name in association with a particular ancestor.
Eurydolops seymourensis is a new genus and species of polydolopid marsupial found in strata of late Eocene age on Seymour Island, Antarctic Peninsula. It may be the sister taxon of Antarctodolops dailyi, also recovered from the same deposits. The new species, known only from an isolated upper premolar, is much smaller and differently specialized than A. dailyi. Both of these Antarctic species differ from South American forms and suggest that regional differentiation had taken place with respect to the marsupial faunas of South America and peninsular Antarctica by late Eocene time. The time of greatest potential dispersal by land mammals between South America and Antarctica in the Tertiary Period may have been about late Paleocene, ca. 60 Ma, after which the Seymour Island stocks underwent endemic evolution, with later, and apparently terminal, representatives being preserved in the La Meseta Formation at about 40 Ma. During the Late Cretaceous-late Eocene interval it is likely that only marsupials composed the land mammal population of the Antarctic region, which, by reason of their adaptation to an arboreal habitus, were favored over placental mammals for dispersal (especially in the Late Cretaceous) between South America and Australia through forests dominated by Nothofagus.
The radiation of a diverse array of endemic marsupials, edentates, primates, rodents and "ungulates' has been exceedingly useful for developing a detailed biochronological sequence of about 20 South American Land Mammal Ages (SALMAs), covering much of Cenozoic time. Best estimates for the approximate durations of the SALMAs are: Lujanian, 10 000-800 000 years ago; Ensenadan, 0.8-1.2 Ma; Uquian, 1.5-3.0 Ma; Chapadmalalan, 3.4-4.0 Ma; Montehermosan, 4.0-6.8 Ma; Huayquerian, 6.8-9.0 Ma; Chasicoan, 9.0-10.0(?) Ma; Mayoan, (?) 10.0-11.8 Ma; Laventan, 11.8-13.8 Ma; Colloncuran, 14.0-15.5 Ma; Friasian, uncertain; Santacrucian, 16.3-17.5 Ma; Colhuehuapian, (?)19-21(?) Ma; Deseadan, 24.5-29 Ma; New SALMA ("Tinguirirican'), 31.5-36 Ma; Divisaderan, (?)40-42(?) Ma; Mustersan, (?)45-48(?) Ma; Casamayoran, (?)51-54(?) Ma; Riochican 55.5-57 Ma; Itaboraian, 57.5-59 Ma; Peligran, 61-62.5 Ma; and Tiupampan, 63-64.5 Ma. The South American faunal and floral record can be combined with available geochronologic information to evaluate timing and pattern of major biotic and environmental changes and events. It is clear that Cenozoic terrestrial biotas responded to both global and regional, physical and biotic, changes and events, including major plate tectonic reorganizations and associated biogeographic events, global Eocene-Oligocene boundary events, phases of Andean uplift, Pliocene-Pleistocene Epoch glaciation/climatic changes, etc. -from Authors
Ontogenetic analysis of the dentition in a wide range of marsupials and eutherians provides valuable criteria for assessing tooth homologies among extant therian mammals. In addition, these developmental data offer evidence for the loss of teeth during mammalian evolution. Such studies can distinguish the deciduous or successional nature of individual teeth, even when replacement does not occur postnatally. Ontogenetic analyses also provide evidence for the formation of vestigial deciduous teeth that do not erupt; these rudiments serve as valuable clues to the homologies of some tooth positions that have been lost during mammalian phylogeny. The continued accumulation of developmental data on the pattern of early budding and differentiation of deciduous tooth germs offers useful criteria for identifying tooth class homologies of highly modified teeth, in addition to their bony and occlusal relationships. An important finding of this analysis is that epithelial connections among the deciduous tooth, primary dental lamina, oral epithelium, successional lamina, and successor tooth furnish the most useful criteria for assessing the ontogenetic relationships between a deciduous tooth and its successor. This developmental pattern was used to test recent hypotheses of premolar-molar homologies in marsupials, where it was claimed that no true postcanine tooth replacement occurs. Epithelial connections, however, support the traditional hypothesis that the posterior premolar position is occupied by typical deciduous and successional teeth during ontogeny; this falsifies the hypothesis that five molars occurred primitively in marsupials. Finally, ontogenetic data are considered for testing the hypothesis of serial homology between the postcanine dentition of eutherians and marsupials, and for the occurrence of five premolars primitively in eutherians.
The most complete record of the continental mammal-bearing Cenozoic of South America comes from Argentina (Marshall et al., 1983a, 1984). This record, representing the southernmost part of the continent, became a unique example in which to study the evolutionary events affecting its mammal communities in relation to the outstanding climatic and environmental changes (Pascual, 1984). The main patterns of geological evolution in this southern part of the continent had a profound influence on its mammalian history. The chronostratigraphic diagrams (Figs. 1 and 2) show the geographical and chronological distribution of Cenozoic sedimentary and volcanic rocks in eastern and western Argentina. This lithostratigraphic distributional pattern makes evident the following historical facts:
Fossil land mammals were collected by G. G. Simpson in 1933–1934 at and near the Tapera de López in central Chubut Province, Patagonia, southern Argentina, from rocks now mapped as the Sarmiento Formation. These fossils are assigned to land mammal faunas of Casamayoran (Early Eocene), Mustersan (Middle Eocene), and Deseadan (late Early Oligocene through Early Miocene) age.
⁴⁰ K- ⁴⁰ Ar age determinations of eight basalt and two tuff units associated with the Deseadan age local fauna at Scarritt Pocket establish a geochronologic framework that calibrates the biostratigraphic record at this locality. The radioisotope dates obtained at Scarritt Pocket range from 23.4 Ma to about 21.0 Ma, and equate with earliest Miocene time. The Scarritt Pocket local fauna is the youngest dated Deseadan age fauna yet known in South America.
Seven other localities have, or were reputed to have, local faunas of Deseadan age associated with dated volcanic units. Six of these localities are in Argentina (Gran Barranca, Cerro Blanco, Valle Hermoso, Pico Truncado, Cañadón Hondo, Quebrada Fiera de Malargüe) and one in Bolivia ( Estratos Salla in the Salla-Luribay Basin). The stratigraphic relationships of the volcanic units with these local faunas is discussed, and the taxonomic content of each is reassessed.
The Deseadan Land Mammal Age is defined by the earliest record of the land mammal genus Pyrotherium, which is from below a basalt dated at 33.6 Ma at Pico Truncado. Other early records of Pyrotherium occur below basalts dated at about 29 Ma at the Gran Barranca and Valle Hermoso, and from a 28.5 Ma level of the Estratos Salla. Thus, the lower boundary for Deseadan time is about 34 Ma.
The youngest record of Pyrotherium is in the upper levels of the Estratos Salla dated at about 24 Ma. However, the Scarritt Pocket local fauna, which lacks Pyrotherium, permits placement of the upper boundary for Deseadan time at about 21.0 Ma. Late Deseadan time is surely, and the end of Deseadan time is apparently, marked by the last record of such groups as Proborhyaeninae ( Proborhyaena ), Rhynchippinae ( Rhynchippus ), Archaeohyracidae ( Archaeohyrax ), and the genera Platypittamys (Octodontidae), Scarrittia (Leontiniidae), Propachyrucos and Prohegetotherium (Hegetotheriidae), and Argyrohyrax (Interatheriidae), as these taxa are recorded in the Scarritt Pocket local fauna. Thus, Deseadan time extends from about 34.0 Ma to about 21.0 Ma, making it the Land Mammal Age with the longest known duration in South America.
Fusion of caudal vertebrae in the sauropod dinosaurs Apatosaurus, Diplodocus, and Camarasaurus is explained as the result of ossification of ligaments spanning consecutive centra. The ossification does not involve the intervertebral space or the annulus fibrosus of the disc and therefore represents true bridging. This is verified by not only the gross external appearance, but also by the use of CAT scans and longitudinal section of a fused pair of Diplodocus caudal vertebrae. Fusion of caudal vertebrae in Camarasaurus is reported here for the first time. It is concluded that the fusion is the result of the physiological phenomenon called diffuse idiopathic skeletal hyperostosis (DISH) and therefore is not a pathological response or due to a physical injury. Various proposed hypotheses to explain the function of the fused caudals, such as defense and postural support, are considered untenable. Fusion of caudal vertebrae probably aided in keeping the tail elevated and undoubtedly served a functional role, though the specific nature of that function is presently unknown. Survey of North American specimens indicates that fusion of caudal vertebrae occurs in 50% of the individuals of Apatosaurus and Diplodocus in which the requisite portion of the tail is preserved, whereas this figure for Camarasaurus is about 25%. For this reason it is suggested that fusion of caudal vertebrae may be a sexually dimorphic feature.
THE mid-Cenozoic immigration of rodents and primates to South America (when it was widely isolated by oceans) represents a pre-eminent problem in the biogeographical history of placental mammals. The unexpected discovery of South America's earliest rodent in the central Chilean Andes provides information critical to resolving the source area and primitive morphology of South American caviomorphs, suggesting an African origin for the group. This rodent is part of a new fossil mammal fauna1, the first diverse assemblage known for a critical 15-25 million year gap in the fossil record. We report here that cooccurrence of numerous higher-level taxa otherwise restricted to older or younger intervals identifies this fauna as representing a new biochronological interval preceding the Deseadan (South American Land Mammal Age), previously the earliest occurrence of rodents and primates on the continent. Radioisotopic dating corroborates biostratigraphy in identifying the new Andean rodent as the earliest known from the continent.
A multivariate analysis of the current South American Land-Mammal Ages is used to reanalyse the recognized “faunistic (mammal) units” or chronofaunae that appear related to radical environmental and climatic changes, which we characterize as Faunistic Cycles and Subcycles. The compositional changes recorded in the successive Faunistic Cycles reflect regional environmental and climatic variations, thus patterns of climatic change. Basically we used cheek teeth of ungulates—natives and immigrants—as an indicator of dietary preference. We then try to infer the structure of successive fossil ungulate communities to deduce the structure of their associated vegetation, and thus the prevailing climatic conditions. We also used other native mammals that followed similar dental modifications, e.g., some rodents and some marsupials, and various types of biological and/or geological evidence. These include climate-sensitive or ecologically specific animals or plants, changes of regional distribution and lithological features of the mammal-bearing formations, diastrophic events, changes in global marine temperatures, and sea-level changes, to contrast those climatic and environmental inferences.
We conclude that: (1) From the oldest to the youngest cycles the ungulates changed from browser sylvan types to predominantly open country and grazer types as warm, humid sylvan environments became drier and more temperate. (2) The earliest mammal communities (Paleocene-Eocene), excluding the peculiar Cochabambian Cycle, show a higher diversity but are composed of taxa with less extreme morphological differences. Even mammals placed in different orders were not nearly as dissimilar as their later counterparts. This relationship gradually became reversed within the later communities, i.e., lower diversity but taxa with more extreme morphological differences; that is, mammals placed in separate orders became more divergent. (3) According to the record of mammals as well as other climate-sensitive organisms, warm and relatively humid forested environments had a wider latitudinal range, stretching at the very least to the northern part of the Antarctic Peninsula. (4) With some regional range fluctuations, Palcogene and Early Miocene tropical to subtropical environments remained very well represented as far as the southern tip of the continent. (5) The Middle Miocene mammals (beginning of the Panaraucanian Faunistic Cycle) indicate that favorable environments were shifted to northern Patagonia and that many climate-sensitive mammals (including platyrrhine monkeys) disappeared from Patagonia, in correlation with the waning or extinction of many taxa related to subtropical woodlands. (6) Mammals of the Panaraucanian Cycle and the Pampian Subcycle clearly indicate that this was the time of the most extensive open-country environments, progressively ranging from wetter subtropical savannas to cold-temperate steppe-like habitats. Most of the mammals of this time were savanna-adapted or steppe-adapted elements. (7) Mammals representing the Postpampian Subcycle attest to the wide swings and cyclicity of the Cenozoic climates. (8) According to the Brazilian mammal records, as well as other biological evidence from the isthmian region, the rainy forested areas characterizing those regions evolved quite recently, by the latest Pleistocene to Recent times.
— Several prominent cladists have questioned the importance of fossils in phylogenctic inference, and it is becoming increasingly popular to simply fit extinct forms, if they are considered at all, to a cladogram of Recent taxa. Gardiner's (1982) and Løvtrup's (1985) study of amniote phylogeny exemplifies this differential treatment, and we focused on that group of organisms to test the proposition that fossils cannot overturn a theory of relationships based only on the Recent biota. Our parsimony analysis of amniote phylogeny, special knowledge contributed by fossils being scrupulously avoided, led to the following best fitting classification, which is similar to the novel hypothesis Gardiner published: (lepidosaurs (turtles (mammals (birds, crocodiles)))). However, adding fossils resulted in a markedly different most parsimonious cladogram of the extant taxa: (mammals (turtles (lepidosaurs (birds, crocodiles)))). That classification is like the traditional hypothesis, and it provides a better fit to the stratigraphic record. To isolate the extinct taxa responsible for the latter classification, the data were successively partitioned with each phylogenetic analysis, and we concluded that: (1) the ingroup, not the outgroup, fossils were important; (2) synapsid, not reptile, fossils were pivotal; (3) certain synapsid fossils, not the earliest or latest, were responsible. The critical nature of the synapsid fossils seemed to lie in the particular combination of primitive and derived character slates they exhibited. Classifying those fossils, along with mammals, as the sister group to the lineage consisting of birds and crocodiles resulted in a relatively poor fit to data; one involving a 2—4 fold increase in evolutionary reversals! Thus, the importance of the critical fossils, collectively or individually, seems to reside in their relative primitive-ness, and the simplest explanation for their more conservative nature is that they have had less time to evolve. While fossils may be important in phylogenetic inference only under certain conditions, there is no compelling reason to prejudge their contribution. We urge systematists to evaluate fairly all of the available evidence.
A diverse vertebrate fauna including representatives of at least 22 families of land mammals is known from 500+m thick Estratos Salla of Deseadan (early Oligocene) age in the Salla-Luribay Basin, about 90 km SW of La Paz, Bolivia. Eight principal fossil levels are identified west of Salla concentrated within a 160 m section. A preliminary report on the geology of the Estratos Salla is given, with maps and stratigraphic sections of the fossiliferous levels and localities. Four specimens of fossil marsupials from the Salla-Luribay Basin in the GEOBOL collection in La Paz are described. Part of a mandibular ramus with two molars represents a new borhyaenid (Sallacyon hoffstetteri gen. et sp. nov.); a relatively complete mandible with teeth is refered to the borhyaenid Notogale mitis (Ameghino, 1897); an associated upper and lower dentition is referred to the palaeothentine (Caenolestidae) Palaeothentes boliviensis Patterson & Marshall, 1978; and a maxillary fragment with poorly preserved M1–4 apparently represents an enormous palaeothentine.
A review of paleontological, phyletic, geophysical, and climatic evidence leads to a new scenario of land mammal dispersal among South America, Antarctica, and Australia in the Late Cretaceous to early Tertiary epochs. New fossil land vertebrate material has been recovered from all three continents in recent years. As regards Gondwana, the present evidence suggests that monotreme mammals and ratite birds are of Mesozoic origin, based on both geochronological and phyletic grounds. The occurrence of monotremes in the early Paleocene (ca. 62 Ma) faunas of Patagonia and of ratites in late Eocene (ca. 41-37 m.y.) faunas of Seymour Island (Antarctic Peninsula) probably is an artifact of a much older and widespread Gondwana distribution prior to the Late Cretaceous Epoch. Except for South American microbiotheres being australidelphians, marsupial faunas of South America and Australia still are fundamentally disjunct. New material from Seymour Island (Microbiotheriidae) indicates the presence there of a derived taxon that resides in a group that is the sister taxon of most Australian marsupials. There is no compelling evidence that dispersal between Antarctica and Australia was as recent as ca. 41 Ma or later. In fact, the derived marsupial and placental land mammal fauna of Seymour Island shows its greatest affinity with Patagonian forms of Casamayoran age (ca. 51–54 m.y.). This suggests an earlier dispersal of more plesiomorphic marsupials from Patagonia to Australia via Antarctica, and vicariant disjunction subsequently. This is consistent with geophysical evidence that the South Tasman Rise was submerged by 64 Ma and with geological evidence that a shallow water marine barrier was present from then onward. The scenario above is consistent with molecular evidence suggesting that australidelphian bandicoots, dasyurids, and diprotodontians were distinct and present in Australia at least as early as the 63-Ma-old australidelphian microbiotheres and the ancient but not basal australidelphian,Andinodelphys, in the Tiupampa Fauna of Bolivia. Land mammal dispersal to Australia typically has been considered to be at a low level of probability (e.g., by sweepstakes dispersal). This study suggests that the marsupial colonizers of Australia included already recognizable members of the Peramelina, Dasyuromorphia, and Diprotodontia, at least, and entered via a filter route rather than by a sweepstakes dispersal.
A reassessment of the geologic and land-mammal fossil evidence used in attribution of a tectosedimentary episode in the Andes between 32 and 37°S to the Middle Eocene “Incaic tectonic phase” of Peru indicates that the episode occurred during Late Oligocene-Early Miocene times(~ 27-20 Ma). From west to east, three structural domains are recognized for this time span in the study area: a volcanic arc (Chile); a thin-skinned, E-verging fold-thrust belt (Cordillera Principal, Chile-Argentina border strip); and a foreland basin (Argentina). Initiation of thrusting in the Cordillera Principal fold-thrust belt produced the coeval initiation of sedimentation in the foreland basin of adjacent Argentina. This onset of foreland deposition postdates strata bearing a Divisaderan Land Mammal Age fauna (i.e. ~ 35-30 Ma) and is marked at ~ 36°30′S by the base of the “Rodados Lustrosos” conglomerates, which are conformably overlain by sedimentary rocks containing a Deseadan Land Mammal Age fauna (i.e. ~ 29-21 Ma). Geologic relationships between the thick volcanic Abanico (Coya-Machalí) and Farellones formations also demonstrate that this tectosedimentary episode practically ended at ~ 20 Ma at least in the volcanic arc, and was therefore roughly coeval with the major tectonic crisis (~ 27-19 Ma) known in northwestern Andean Bolivia some 1500 km to the north. This strongly suggests that a long, outstanding tectonic upheaval affected at least an extended 12–37°S segment of the Andean margin of South America during Late Oligocene and Early Miocene times.
Griffiths, G. C. D. (Department of Entomology, University of Alberta, Edmonton, Alberta T6G 2E3, Canada) 1976. The future of Linnaean nomenclature. Syst. Zool. 25:168–173 .—Linnaean nomenclature in its present form cannot represent phylogenies unambiguously when fossil species are included. It is possible to avoid this difficulty by discontinuing the classification of taxa into Linnaean categories. The features of the resulting unclassified hierarchy and the way in which newly discovered taxa may be inserted in it are explained. Taxa may be classified in different ways, for instance into age classes or into evolutionary grades. The Linnaean category names, with their essentialist connotations, are inappropriate in either case. The international codes of nomenclature should be concerned primarily with the rules for naming taxa and should not prescribe how classes (categories) should be named and used. The prescription of suffices to indicate categorical rank conflicts with the stated aim of the codes to promote stability of nomenclature, and should be discontinued. While binomial nomenclature will surely be retained, a difference of logical status between the forenames of Quaternary and earlier species will need to be recognized.
- Marshall L. G.