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Dispersal of Vertebrates from Between the Americas, Antarctica, and Australia in the Late Cretaceous and Early Cenozoic
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The early Paleocene diversity of metatherians in Tiupampan faunas of South America and the pre-Tiupampan Paleocene polydolopimorphian Cocatherium speak in favor of an earliest Paleocene or Late Cretaceous dispersal of metatherians from North America. No Late Cretaceous metatherian or eutherian mammals have been recovered to date in South America, but the late Campanian to Maastrichtian hadrosaurine dinosaurs in Argentina, as well as the late Maastrichtian of the Antarctic Peninsula, is evidence of a biotic connection to North America. Placental ‘condylarths’ in the Tiupampan may have been related to, and dispersed southward relative to, Puercan taxa in North America and perhaps reflect a somewhat later event in comparison to metatherians. Other than hadrosaurine dinosaurs, Late Cretaceous vertebrates of South America are basically Gondwanan in affinities and reflect (and survived) the pre-106 Ma connection between South America, Africa, and Antarctica. The potential for a Late Cretaceous dispersal of metatherians would be compatible with a continued dispersal to Australia at that time, also supported by plate tectonic relationships, notwithstanding the basically endemic coeval Australian dinosaur fauna, and recognizing the essential absence of a Late Maastrichtian land vertebrate record there. An early Paleocene connection between at least Antarctica and South America is documented by the presence of a monotreme in the Peligran fauna of Patagonia. This, coupled with the fact that post-Peligran mammal faunas in South America and the Antarctic Peninsula (from at least 52 Ma in that location) are composed of derived metatherian as well as placental mammals, suggests that dispersal of metatherians to Australia had been achieved prior to the Eocene. Such timing is compatible with the still plesiomorphic level of Australian metatherians from the early Eocene Tingamarra fauna of Australia, the marine sundering of the Tasman Gate at about 50 Ma and the development of a continuously marine southern coastline of Australia from about 45 Ma effectively foreclosed overland mammal and other vertebrate dispersal to Australia thereafter.
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... Furthermore, Oliveira and Goin (2011) and Carneiro (2019) linked the apparently "short-time" evolutionary history of protodidelphids with the paleoenvironmental changes that resulted from the events of the PETM (around 55.50 Ma; Bowen et al., 2015), which increased global temperatures and tropical biomes throughout South America during the early Eocene (Woodburne et al., 2014a;Goin et al., 2016), primarily due to the increase in global temperatures (see Tarquini et al., 2022). Carneiro (2019) commented that the occurrence of several protodidelphids with different degrees of bunodonty in a single locality (the Itaboraí Basin) would support a "rapid" evolutionary diversification for this clade after the PETM. ...
... Carolopaulacoutoia sp. nov., Gashternia carioca Goin andOliveira, 2007, andEpidolops ameghinoi (see Marshall, 1987;Goin et al., 1998;Goin and Oliveira, 2007;Goin, 2011, 2012;Zimicz, 2012;Goin et al., 2016;Carneiro, 2019;Carneiro and Oliveira, 2023). ...
... The last (and most recent) occurrence of this group is recorded for the middle Eocene of Argentina (Protodidelphis; see Tejedor et al., 2009), an observation that could be linked with a reduction in the global temperatures after the Early Eocene Climatic Optimum (EECO). During the middle Eocene, the extensive tropical forests that covered most of the South American continent were replaced by "savanna-like" environments (Woodburne et al., 2014a(Woodburne et al., , 2014bGoin et al., 2016), with an increase in the diversity of terrestrial mammals, hypsodont metatherians and several taxa with granivorous or herbivorous diets (Goin et al., 2010). Therefore, this environmental turnover could be related to the disappearance of the protodidelphids in the fossil record after the early middle Eocene. ...
Carolocoutoia ferigoloi is one of the largest metatherians of the Itaboraí fauna (Early Eocene, Southeastern Brazil). It was originally identified from a single upper molar with a markedly bunodont crown, wrinkled enamel, and a robust protocone. Here, we describe a nearly complete right dentary of C. ferigoloi with the alveoli of the premolars and first lower molar, a very worn second lower molar, complete third and fourth lower molars, and a right second upper molar. Carolocoutoia differs from other protodidelphids in having inflated, conical trigonid cusps, a more flattened entoconid, a developed entocristid, and a supernumerary cusp labial to the entoconid. Carolocoutoia was recovered in our phylogenetic analysis as the sister taxon of Protodidelphis ), since both share the presence of an anteriorly recurved dentary, wrinkled enamel, and a sinuous crest between stylar cusps B and D. The inflated, conical trigonid cusps of Carolocoutoia represent an evolutionary convergence with other South American Paleogene mammals, such as some ungulates, and the polydolopimorphian Roberthoffstetteria. We also present the second record of a pathology (molar extrusion) in a metatherian from Itaboraí. Based on its molar crown morphology, Carolocoutoia ferigoloi was a specialized frugivorous metatherian. The occurrence of a specialized frugivorous protodidelphid in the Itaboraí fauna is in line with the well-established increase in global temperatures and the expansion of tropical forests after the Paleocene-Eocene Thermal Maximum (around 55.5–55.3 million years ago).
... Furthermore, Oliveira and Goin (2011) and Carneiro (2019) linked the apparently "short-time" evolutionary history of protodidelphids with the paleoenvironmental changes that resulted from the events of the PETM (around 55.50 Ma; Bowen et al., 2015), which increased global temperatures and tropical biomes throughout South America during the early Eocene (Woodburne et al., 2014a;Goin et al., 2016), primarily due to the increase in global temperatures (see Tarquini et al., 2022). Carneiro (2019) commented that the occurrence of several protodidelphids with different degrees of bunodonty in a single locality (the Itaboraí Basin) would support a "rapid" evolutionary diversification for this clade after the PETM. ...
... Carolopaulacoutoia sp. nov., Gashternia carioca Goin andOliveira, 2007, andEpidolops ameghinoi (see Marshall, 1987;Goin et al., 1998;Goin and Oliveira, 2007;Goin, 2011, 2012;Zimicz, 2012;Goin et al., 2016;Carneiro, 2019;Carneiro and Oliveira, 2023). ...
... The last (and most recent) occurrence of this group is recorded for the middle Eocene of Argentina (Protodidelphis; see Tejedor et al., 2009), an observation that could be linked with a reduction in the global temperatures after the Early Eocene Climatic Optimum (EECO). During the middle Eocene, the extensive tropical forests that covered most of the South American continent were replaced by "savanna-like" environments (Woodburne et al., 2014a(Woodburne et al., , 2014bGoin et al., 2016), with an increase in the diversity of terrestrial mammals, hypsodont metatherians and several taxa with granivorous or herbivorous diets (Goin et al., 2010). Therefore, this environmental turnover could be related to the disappearance of the protodidelphids in the fossil record after the early middle Eocene. ...
Carolocoutoia ferigoloi Goin et al., 1998, is one of the largest metatherians of the Itaboraí fauna (Early Eocene, Southeastern Brazil). It was originally identified from a single upper molar with a markedly bunodont crown, wrinkled enamel, and a robust protocone. Here, we describe a nearly complete right dentary of C. ferigoloi with the alveoli of the premolars and first lower molar, a very worn second lower molar, complete third and fourth lower molars, and a right second upper molar. Carolocoutoia differs from other protodidelphids in having inflated, conical trigonid cusps, a more flattened entoconid, a developed entocristid, and a supernumerary cusp labial to the entoconid. Carolocoutoia was recovered in our phylogenetic analysis as the sister taxon of Protodidelphis Paula Couto, 1952a, since both share the presence of an anteriorly recurved dentary, wrinkled enamel, and a sinuous crest between stylar cusps B and D. The inflated, conical trigonid cusps of Carolocoutoia represent an evolutionary convergence with other South American Paleogene mammals, such as some ungulates, and the polydolopimorphian Roberthoffstetteria Marshall et al., 1983. We also present the second record of a pathology (molar extrusion) in a metatherian from Itaboraí. Based on its molar crown morphology, Carolocoutoia ferigoloi was a specialized frugivorous metatherian. The occurrence of a specialized frugivorous protodidelphid in the Itaboraí fauna is in line with the well-established increase in global temperatures and the expansion of tropical forests after the Paleocene-Eocene Thermal Maximum (around 55.5-55.3 million years ago).
... Considering the fauna from Laguna Fría, Nemolestes lagunafriensis shared the hypercarnivorous niche with a "putative hathliacynid" (unnamed clade A?) and a borhyaenoid (see Tejedor et al. 2009). Other metatherian members of this fauna, such as derorhynchids and "peradectoids", are considered insectivorous (Zimicz 2012;Goin et al. 2016;Oliveira et al. 2021); Protodidelphis, Procaroloameghinia? and Palangania are considered as insectivorous/frugivorous (Goin et al. 1998;Oliveira and Goin 2011;Zimicz 2012;Carneiro 2019); and Itaboraidelphys is considered a hypocarnivorous/omnivorous taxon (see Zimicz 2012). ...
... Therefore, the Eocene diversity of sparassodonts should be greater than expected (see a similar conclusion in Croft et al. 2018;Engelman et al. 2018). Furthermore, the apparently "short-time" evolutionary history of sparassodonts in South America should be directly linked with the paleoenvironmental changes resulted from the events of the Paleocene-Eocene Thermal Maximum (around 55.5 Ma; Bowen et al. 2015), which increased global temperatures and tropical biomas throughout South America during the early Eocene (Woodburne et al. 2014;Goin et al. 2016), mostly due to the increase in the global temperatures (see e.g., Tarquini et al. 2022). The results of our phylogenetic analysis argue in favor of the hypothesis that linked the increase in diversity of metatherians with the climatic modifications during the early Eocene (see Tarquini et al. 2022), which has been linked to the increase in abundance of polydolopimorphians (Goin et al. 2016) and increase in diversity of protodidelphids (Carneiro 2019). ...
... Furthermore, the apparently "short-time" evolutionary history of sparassodonts in South America should be directly linked with the paleoenvironmental changes resulted from the events of the Paleocene-Eocene Thermal Maximum (around 55.5 Ma; Bowen et al. 2015), which increased global temperatures and tropical biomas throughout South America during the early Eocene (Woodburne et al. 2014;Goin et al. 2016), mostly due to the increase in the global temperatures (see e.g., Tarquini et al. 2022). The results of our phylogenetic analysis argue in favor of the hypothesis that linked the increase in diversity of metatherians with the climatic modifications during the early Eocene (see Tarquini et al. 2022), which has been linked to the increase in abundance of polydolopimorphians (Goin et al. 2016) and increase in diversity of protodidelphids (Carneiro 2019). ...
Nemolestes and Procladosictis are Eocene sparassodonts of controversial affinities. Nevertheless, despite the poor preservation of their holotypes, several other specimens have been tentatively assigned to these genera, as exemplified by some
isolated teeth from the Itaboraí and Laguna Fría faunas. Here, we revise specimens referred to Nemolestes and Procladosictis from Itaboraí, Laguna Fría and Ameghino’s collection. Nemolestes differs from Patene in its more reduced metaconid, and “carnassialized” m4 (with reduced talonid and talonid cuspids, except the hypoconulid), features that make it possible to identify specimens from Itaboraí and Laguna Fría as Nemolestes. This taxon occurred from the early Eocene (Itaboraian SALMA) to the middle Eocene (Casamayoran SALMA). Nemolestes represents the oldest known hypercarnivorous sparassodont. The inclusion of Nemolestes and Procladosictis in a comprehensive phylogenetic analysis recovered them in a polytomy as the sister taxa of Borhyaenoidea and a new unnamed clade that includes Lycopsis, Dukecynus, Hathliacynidae, Hondadelphys and Stylocynus. Nemolestes shares with these taxa, but not Patene, the presence of a “carnassialized” m4. Nemolestes differs from known borhyaenoids in the absence of a medially positioned protoconid and short anterolabial cingulid. Therefore, Nemolestes is an early lineage of Sparassodonta. “Procladosictis erecta” is a lower premolar of the unnamed clade, as it shows symmetric walls and a small precingulid. "Procladosictis erecta" should be, in fact, referred to Procladosictis. Our phylogenetic analysis indicates that during the early middle Eocene (Laguna Fría and La Barda faunas), the unnamed clade and Borhyaenoidea had already diverged. Therefore, the evolutionary history of these groups is older than previously thought.
... Thus, the warm climate and widespread boreotropical flora may have facilitated exchanges of Cissampelideae between Asia and North America. Fossil evidence from hadrosaurs, condylarth and didelphimorph mammals suggests that a connecting land bridge, i.e. the Antillean volcanic arc system (Iturralde-Vinent, 2006), consisting of non-volcanic and volcanic islands, appeared in the shallow sea between North and South America during the latest Campanian/Maastrichtian (~75-66 Ma; Gayet et al., 1992;Goin et al., 2016). Thus, Cissampelideae might have dispersed southwards into South America from North America via the Antillean volcanic arc system. ...
The integration of morphological and molecular data is essential to understand the affinities of fossil taxa and spatio‐temporal evolutionary processes of organisms. However, homoplastic morphological characters can mislead the placement of fossil taxa and impact downstream analyses. Here, we provide an example of how to mitigate effectively the effect of morphological homoplasy on the placement of fossil taxa and biogeographic inferences of Cissampelideae. We assembled three data types, morphological data only, morphological data with a molecular scaffold and combined morphological and molecular data. By removing high‐level homoplastic morphological data or reweighting the morphological characters, we conducted 15 parsimony, 12 undated Bayesian and four dated Bayesian analyses. Our results show that the 14 selected Cissampelideae fossil taxa are placed poorly when based only on morphological data, but the addition of molecular scaffold and combination of morphological and molecular data greatly improve the resolution of fossil nodes. We raise the monotypic Stephania subg. Botryodiscia to generic status and discover that three fossils previously assigned to Stephania should be members of Diploclisia . The Bayesian tip‐dated tree recovered by removing homoplastic morphological characters with a Rescaled Consistency Index <0.25 has the highest stratigraphic fit and consequently generates more reasonable biogeographic reconstruction for Cissampelideae. Cissampelideae began to diversify in Asia in the latest Cretaceous and subsequently dispersed to South America around the Cretaceous–Palaeogene boundary. Two dispersal events from Asia to Africa occurred in the Early Eocene and the Late Eocene–Late Oligocene, respectively. These findings provide guidelines and practical methods for mitigating the effects of homoplastic morphological characters on fossil placements and Bayesian tip‐dating, as well as insights into the past tropical floristic exchanges among different continents.
... This is particularly true for Palaeogene assemblages, since several groups underwent dramatic radiations after the Early Eocene Climatic Optimum (EEOC) and as a response to the changing conditions linked to the climatic deterioration toward the end of the Eocene (Woodburne et al., 2014). At that time, a worldwide cooling event was triggered by the isolation of South America and the Antarctic glaciation, at the threshold of the Eocene-Oligocene boundary (Goin et al., 2016;Woodburne et al., 2014). This scenario produced more temperate conditions and a change in the configuration of the landscape led by the development of open areas (Croft et al., 2003 and references therein). ...
Here we describe a new notoungulate taxon, Pascualhyrax irqi sp. nov., from Eocene levels of north-western Argentina. The materials studied include cranial and dental remains and were exhumed in sediments of the Quebrada de los Colorados Formation, corresponding to the late middle Eocene (Bartonian). General traits of the referred specimens (e.g. hypsodont postcanines, nasal bulge) point to a close relationship with different typotherian taxa traditionally included among the paraphyletic ‘Archaeohyracidae’. In turn, a combination of characters indicates that the new material represents a new taxon (e.g. smaller size, deep ectoflexus in upper molars in all wear stages, maxillary process extending posterior to the caudal end of the nasals). A phylogenetic analysis was performed, based in a previously published matrix and the addition of new characters, resulting in a close relationship of Pascualhyrax irqi sp. nov. with different ‘Archaeohyracidae’ of Oligocene radiation. This fact shows the early expression of some characters until now only known for later forms, and developed in the context of a recently acknowledged diversity of hypsodont typotherians in north-western Argentina. Regarding other evolutionary issues, the strong similitude of the juvenile specimens referred to Pascualhyrax irqi sp. nov. with adult individuals of the Neogene clade Pachyrukhinae, indicates possible heterochronic (paedomorphic) traits in the later forms.
The Itaboraí Basin, municipality of Itaboraí, Rio de Janeiro state, Brazil, preserved an Early Eocene vertebrate assemblage. Among its representatives, Metatheria comprises its most diverse clade, with a minimum of 29 genera and 43 species. Considering this diversity, large-sized taxa (based on didelphid standards, i.e., between 1 kg and 3.3 kg) are represented by Didelphopsis, Protodidelphis, and Patene, each considered to have explored different trophic niches. However, the discovery of a new large-sized metatherian from this locality, here named Xenocynus crypticus gen. et sp. nov., indicates that the trophic complexity of Itaboraí’s metatherians could not be so well-defined. Xenocynus crypticus gen. et sp. nov. is identified by the presence of its reduced StD, long postmetacrista, short protocone, talonid's area much smaller than the one of trigonid, spaced paraconid and metaconid (bases are not in contact), molar series increasing in size from m1 to m4, deep maxillary pits between upper molars, and robust symphysis. We included Itaboraidelphys camposi, X. crypticus gen. et sp. nov., and other large-sized taxa in two PCA analyses, the first considering morphometric measurements and the second considering some morphofunctional indexes, to test their placement in morphospace. Our analyses indicated that these taxa exhibit distinctive morphometric and morphofunctional patterns, suggesting low trophic niches overlapping between them. The results indicate that X. crypticus gen. et sp. nov. was a generalized carnivore (insectivory-carnivory), more specialized than the insectivorous/omnivorous Itaboraidelphys camposi, but less specialized than the larger Patene simpsoni, a carnivorous taxon.
Diprotodontians are the morphologically and ecologically most diverse order of marsupials. However, an approximately 30-million-year gap in the Australian terrestrial vertebrate fossil record means that the first half of diprotodontian evolution is unknown. Fossil taxa from immediately either side of this gap are therefore critical for reconstructing the early evolution of the order. Here we report the likely oldest-known koala relatives (Phascolarctidae), from the late Oligocene Pwerte Marnte Marnte Local Fauna (central Australia). These include coeval species of Madakoala and Nimiokoala, as well as a new probable koala (?Phascolarctidae). The new taxon, Lumakoala blackae gen. et sp. nov., was comparable in size to the smallest-known phascolarctids, with body-mass estimates of 2.2-2.6 kg. Its bunoselenodont upper molars retain the primitive metatherian condition of a continuous centrocrista, and distinct stylar cusps B and D which lacked occlusion with the hypoconid. This structural arrangement: (1) suggests a morphocline within Phascolarctidae from bunoselenodonty to selenodonty; and (2) better clarifies the evolutionary transitions between molar morphologies within Vombatomorphia. We hypothesize that the molar form of Lumakoala blackae approximates the ancestral condition of the suborder Vombatiformes. Furthermore, it provides a plausible link between diprotodontians and the putative polydolopimorphians Chulpasia jimthorselli and Thylacotinga bartholomaii from the early Eocene Tingamarra Local Fauna (eastern Australia), which we infer as having molar morphologies consistent with stem diprotodontians.
Metatherians represented the most diverse group of Paleogene mammals of South America. The early Eocene metatherian fauna of Itaboraí, Brazil, was one of the most prominent. This fauna preserved a great diversity of tiny and very small insectivore assemblages, specialized durophagous, and brachydont-bunodont metatherians and is represented by 29 genera and 39 species, which are tooth-based taxa. The fauna preserved the oldest confirmed representatives of Didelphimorphia, as well as possible stem-Paucituberculata, but with no confirmed Australidelphia. Furthermore, the probable presence of the North American Late Cretaceous groups in the fauna, such as Pediomyoidea, Hatcheriformes, and Stagodontidae is also discussed. Sparassodonts, such as Patene, represented the top mammalian predators of the fauna. The large variety of Itaboraian “ameridelphians” includes, among others, “peradectoids,” caroloameghinioids, jaskhadelphyids, and sternbergiids, which represented earlier metatherian clades than the marsupials. Polydolopimorphians were represented by Epidolops, the most abundant metatherian of this fauna, and Gashternia. Caroloameghinioids should not be assigned to Didelphimorphia, and is here regarded as “peradectoids.” Derorhynchidae was the sister taxon of Herpetotheriidae. The reassessment of the eight petrosal morphotypes recovered in Itaboraí supports the common origin for the majority of South American clades and has enabled their reassessment to representatives of this fauna.
In the dusk of the Mesozoic, advanced duck-billed dinosaurs (Hadrosauridae) were so successful that they likely outcompeted other herbivores, contributing to declines in dinosaur diversity. From Laurasia, hadrosaurids dispersed widely, colonizing Africa, South America, and, allegedly, Antarctica. Here, we present the first species of a duck-billed dinosaur from a subantarctic region, Gonkoken nanoi, of early Maastrichtian age in Magallanes, Chile. Unlike duckbills further north in Patagonia, Gonkoken descends from North American forms diverging shortly before the origin of Hadrosauridae. However, at the time, non-hadrosaurids in North America had become replaced by hadrosaurids. We propose that the ancestors of Gonkoken arrived earlier in South America and reached further south, into regions where hadrosaurids never arrived: All alleged subantarctic and Antarctic remains of hadrosaurids could belong to non-hadrosaurid duckbills like Gonkoken. Dinosaur faunas of the world underwent qualitatively different changes before the Cretaceous-Paleogene asteroid impact, which should be considered when discussing their possible vulnerability.
Did the end-Cretaceous mass extinction event, by eliminating non-avian dinosaurs and most of the existing fauna, trigger the evolutionary radiation of present-day mammals? Here we construct, date and analyse a species-level phylogeny of nearly all extant Mammalia to bring a new perspective to this question. Our analyses of how extant lineages accumulated through time show that net per-lineage diversification rates barely changed across the Cretaceous/Tertiary boundary. Instead, these rates spiked significantly with the origins of the currently recognized placental superorders and orders approximately 93 million years ago, before falling and remaining low until accelerating again throughout the Eocene and Oligocene epochs. Our results show that the phylogenetic 'fuses' leading to the explosion of extant placental orders are not only very much longer than suspected previously, but also challenge the hypothesis that the end-Cretaceous mass extinction event had a major, direct influence on the diversification of today's mammals. Molecular data and the fossil record can give conflicting views of the evolutionary past. For instance, empirical palaeontological evidence by itself tends to favour the 'explosive model' of diversification for extant placental mammals 1 , in which the orders with living representatives both originated and rapidly diversified soon after the Cretaceous/Tertiary (K/T) mass extinction event that eliminated non-avian dinosaurs and many other, mostly marine 2 , taxa 65.5 million years (Myr) ago 1,3,4. By contrast, molecular data consistently push most origins of the same orders back into the Late Cretaceous period 5-9 , leading to alternative scenarios in which placental line-ages persist at low diversity for some period of time after their initial origins ('phylogenetic fuses'; see ref. 10) before undergoing evolutionary explosions 1,11. Principal among these scenarios is the 'long-fuse model' 1 , which postulates an extended lag between the Cretaceous origins of the orders and the first split among their living representatives (crown groups) immediately after the K/T boundary 8. Some older molecular studies advocate a 'short-fuse model' of diversification 1 , where even the basal crown-group divergences within some of the larger placental orders occur well within the Cretaceous period 5-7. A partial molecular phylogeny emphasizing divergences among placental orders suggested that over 20 lineages with extant descendants (henceforth, 'extant lineages') survived the K/T boundary 8. However, the total number of extant lineages that pre-date the extinction event and whether or not they radiated immediately after it remain unknown. The fossil record alone does not provide direct answers to these questions. It does reveal a strong pulse of diversification in stem eutherians immediately after the K/T boundary 4,12 , but few of the known Palaeocene taxa can be placed securely within the crown groups of extant orders comprising Placentalia 4. The latter only rise to prominence in fossils known from the Early Eocene epoch onwards (,50 Myr ago) after a major faunal reorganization 4,13,14. The geographical patchiness of the record complicates interpretations of this near-absence of Palaeocene crown-group fossils 14-16 : were these clades radiating throughout the Palaeocene epoch in parts of the world where the fossil record is less well known; had they not yet originated; or did they have very long fuses, remaining at low diversity until the major turnover at the start of the Eocene epoch? The pattern of diversification rates through time, to which little attention has been paid so far, might hold the key to answering these questions. If the Cretaceous fauna inhibited mammalian diversification , as is commonly assumed 1 , and all mammalian lineages were able to radiate after their extinction, then there should be a significant increase in the net per-lineage rate of extant mammalian diversification , r (the difference between the per-lineage speciation and extinction rates), immediately after the K/T mass extinction. This hypothesis, along with the explosive, long-and short-fuse models, can be tested using densely sampled phylogenies of extant species, which contain information about the history of their diversification rates 17-20. Using modern supertree algorithms 21,22 , we construct the first virtually complete species-level phylogeny of extant mammals from over 2,500 partial estimates, and estimate divergence times (with confidence intervals) throughout it using a 66-gene alignment in conjunction with 30 cladistically robust fossil calibration points. Our analyses of the supertree indicate that the principal splits underlying the diversification of the extant lineages occurred (1) from 100-85 Myr ago with the origins of the extant orders, and (2) in or after the Early Eocene (agreeing with the upturn in their diversity known from the fossil record 4,13,14), but not immediately after the K/T boundary, where diversification rates are unchanged. Our findings-that more extant placental lineages survived the K/T boundary than previously recognized and that fewer arose immediately after it than previously suspected-extend the phylogenetic fuses of many extant orders and indicate that the end-Cretaceous mass extinction event had, at best, a minor role in driving the diversification of the present-day mam-malian lineages. A supertree with divergence times for extant mammals The supertree contains 4,510 of the 4,554 extant species recorded in ref. 23, making it 99.0% complete at the species level (Fig. 1; see also
The ichnological assemblage from the Estancia Laguna Manantiales, from the Middle Jurassic La Matilde Formation, Santa Cruz province, Argentina, is exceptional both in diversity and abundance. It is composed of mammal, dinosaur, invertebrate, and root traces. The most significant and abundant specimens are those assigned to the ichnogenus Ameghinichnus Casamiquela, 1961. This ichnogenus is revised and an emendation of its diagnosis is suggested. The inclusion of all the known specimens to the type ichnospecies, Ameghinichnus patagonicus Casamiquela, 1961, is challenged and some specimens are placed in a new ichnospecies, Ameghinichnus manantialensis isp. nov. Similar tracks from other ichnological localities worldwide were previously referred to Ameghinichnus, but only Eopentapodiscus (Ellenberger, 1970), from South Africa is considered as a junior synonym of Ameghinichnus. The ichnotaxobases used to classify tracks with mammalian affinities at ichnogeneric and ichnospecific levels are evaluated and re-assessed ichnotaxonomic criteria are proposed. Different criteria used to distinguish mammalian imprints from non-mammalian tracks are commented.
A new genus and species, Patagosmilus goini, of the family Thylacosmilidae (Mammalia, Metatheria, Sparassodonta) is described here. The new taxon is based on a single specimen collected from the west margin of the Río Chico, in Río Negro Province, Argentina, from the middle Miocene Colloncuran SALMA. Until now, two formally recognized species were encompassed in the family Thylacosmilidae: Thylacosmilus atrox, from the late Miocene-late Pliocene Huayquerian to Chapadmalalan SALMAof Argentina and probably Uruguay; and Anachlysictis gracilis, from the middle Miocene Laventan SALMA of Colombia. Recognition of the Patagonian taxon, Patagosmilus, provides new anatomical data, likely to be included in future phylogenetic analyses. The overall morphology of Patagosmilus suggests that it has a more generalized anatomy than Thylacosmilus. The dental morphology suggests the new Patagonian taxon was probably closer to Thylacosmilus than Anachlysictis. Saber-tooth thylacosmilids have several autapomorphic features in the skull that differentiate them from other sparassodonts, including the delayed replacement or non-replacement of the deciduous last premolar.
