Fig 5 - uploaded by Marcelo R Sánchez-Villagra
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Stereo photographs of upper and lower molars of A) Harpiocephalus harpia (ZMB 90376) and B) Kerivoula picta (ZMB 48567). Scale bar equals 2 mm. See Fig. 1 for numbering.
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We review the evolution of dental zalambdodonty across therian mammals. Among zalambdodonts, there is little or no occlusion
between the protocone and talonid basin and one of the central cusps of the upper molars (metacone or paracone) and the talonid
basin of the lower molars are lost or reduced. Over two dozen genera of therian mammals show zala...
Citations
... The hyoid apparatus is particularly derived (Fig. 6), with most species showing a sharply angled and bulbous stylohyoid that articulates with the dentary (Bronner et al. 1990, Bronner 1991. Extant species show lateral extensions of the premaxilla (Fig. 7), are dentally zalambdodont, and lack upper molar metacones, with reduced (and sometimes absent) lower molar talonids (Fig. 8;Butler 1937, Asher and Sánchez-Villagra 2005, Asher 2019). Chrysochlorids show a tightly coiled cochlea with three or more turns (Crumpton et al. 2015), and some species exhibit enormous mallei and elongated incudes (Fig. 9;Forster-Cooper 1928, Simonetta 1968, von Mayer et al. 1995, Mason 2003, 2004, Mason et al. 2017. ...
We undertook a phylogenetic analysis of genetic and anatomical data focusing on golden moles (Chrysochloridae) and tenrecs (Tenrecidae). Our results support the now well-resolved topology for extant tenrecids, in addition to the paraphyly of ‘Chrysochlorinae’ and the genera Chrysochloris and Chlorotalpa as traditionally used. Carpitalpa arendsi is the sister taxon to Neamblysomus; together, they compose the sister clade of Amblysomus. Unexpectedly, Calcochloris obtusirostris is the sister taxon of Chrysospalax. The oldest divergence within crown Chrysochloridae is likely to be the node separating Eremitalpa–Huetia or Eremitalpa alone from the remaining species. A Chrysochloris–Cryptochloris root appears most frequently under equally weighted parsimony or with few or no sampled tenrecids, suggesting that it is artefactual. The tropical genus Huetia is among the most widely distributed and anatomically polymorphic in our sample. Eremitalpa and Huetia have a relatively unspecialized hyoid apparatus and short angular process of the dentary. These elements in Huetia show a particular resemblance to those of the Namibian fossil Namachloris, which we reconstruct as a stem chrysochlorid. Crown chrysochlorids are geologically younger than crown tenrecids and probably diversified in the Miocene around the same time as the tenrecid genus Microgale. Fossils of both groups from Eocliff in Namibia are probably late Eocene to early Miocene in age.
... Tribosphenic molars have been retained by numerous lineages of small insectivorous therians, but several therian lineages show a distinctive modification of this ancestral pattern termed 'zalambdodonty'. Zalambdodonty presents in which either the paracone or metacone are greatly reduced or lost, giving the molar crown a distinctive V-shape, with the protocone and talonid also often greatly reduced or lost (Asher & S anchez-Villagra 2005). Among eutherians, the zalambdodont condition of the upper molars is typically approached via reduction of the metacone (see for example Seiffert et al. 2007 for discussion of the development of zalambdodonty among afrosoricids). ...
... The exact function of U. whitei's specialized, incipiently zalambdodont dentition is difficult to determine, as few detailed studies of the functional morphology of the dasyurid dentition have been published (but see Sanson 1985 for one example). Although clearly specialized, the exact functional implications of zalambdodont molars are unclear (Asher & S anchez-Villagra 2005). Modern zalambdodont mammals with known diets are broadly faunivorous, most of them preying predominantly on insects. ...
Urrayira whitei gen. et sp. nov. is described based on dental remains from middle Pleistocene cave sites at Mount Etna, Queensland. Its higher-level systematic affinities are unclear but it appears to be a dasyuromorphian. It is unusual in having a specialized reduced dentition characterized by reduction of the stylar cusps, protocone and talonid, resulting in an incipiently zalambdodont morphology that emphasizes the shearing crests. In addition, only two upper premolars are present, and we assume that it is P3 that has been suppressed, as has occurred multiple times within Dasyuridae. Maximum parsimony and undated Bayesian analyses of a 174 morphological character matrix intended to resolve relationships within Dasyuromorphia, with a molecular scaffold enforced, suggest that Urrayira is a dasyurid. In the maximum parsimony analysis, Urrayira is sister to Planigale gilesi (which also lacks P3), whereas in the undated Bayesian analysis, Urrayira resolves as part of a trichotomy at the base of Dasyuridae, together with Sminthopsinae and Dasyurinae; however, support values are generally low throughout the tree. While the majority of rainforest-adapted taxa in the Mount Etna sites became either extinct or were locally extirpated at, or soon after, 280 ka, there is no evidence that U. whitei gen. et sp. nov. even persisted until that time. Urrayira whitei was likely a rainforest-specialist, thus may have been particularly vulnerable to incipient effects of the Mid-Brunhes climatic shift towards aridity that eventually drove the disappearance of the Mount Etna rainforest and its associated fauna.
Jonathan Cramb* [jonathan.cramb@qm.qld.gov.au], Queensland Museum, PO Box 3300, South Brisbane BC, Queensland 4101, Australia; Scott Hocknull [scott.hocknull@qm.qld.gov.au], Queensland Museum, PO Box 3300, South Brisbane BC, Queensland 4101, Australia; Robin M. D. Beck [r.m.d.beck@salford.ac.uk], School of Science, Engineering and Environment, University of Salford, Manchester M5 4WT, UK; Shimona Kealy [shimona.kealy@anu.edu.au], Archaeology and Natural History, College of Asia and the Pacific, The Australian National University, Canberra, ACT, 2601, Australia; Gilbert J. Price [g.price1@uq.edu.au], School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia.
... Tribosphenic molars have been retained by numerous lineages of small insectivorous therians, but several therian lineages show a distinctive modification of this ancestral pattern termed 'zalambdodonty'. Zalambdodonty presents in which either the paracone or metacone are greatly reduced or lost, giving the molar crown a distinctive V-shape, with the protocone and talonid also often greatly reduced or lost (Asher & S anchez-Villagra 2005). Among eutherians, the zalambdodont condition of the upper molars is typically approached via reduction of the metacone (see for example Seiffert et al. 2007 for discussion of the development of zalambdodonty among afrosoricids). ...
... The exact function of U. whitei's specialized, incipiently zalambdodont dentition is difficult to determine, as few detailed studies of the functional morphology of the dasyurid dentition have been published (but see Sanson 1985 for one example). Although clearly specialized, the exact functional implications of zalambdodont molars are unclear (Asher & S anchez-Villagra 2005). Modern zalambdodont mammals with known diets are broadly faunivorous, most of them preying predominantly on insects. ...
Malleodectes? wentworthi, sp. nov. is a highly specialized durophagous marsupial from a Middle Miocene limestone cave deposit in the Riversleigh World Heritage area, northern Australia. It provides the first information regarding the lower dentition of malleodectids, an extinct family of dasyuromorphians. It is also the smallest durophagous member of Metatheria (marsupials and their stem relatives) known to date, with an estimated body mass of ∼70–90 g, an order of magnitude smaller than other known malleodectids (Malleodectes mirabilis and Ma. moenia ∼1 kg). As in other malleodectids, Ma.? wentworthi has a hypertrophied, dome-like premolar specialized for crushing hard foods. Tentative assignment to the genus Malleodectes is based on derived similarities of the premolar and molar dentition to those of larger species of Malleodectes (known only from upper dentitions), and occlusal compatibility. Quantitative morphofunctional analyses of dental indices and mandibular bending strength are congruent with the previously proposed hypothesis that malleodectids may have been uniquely specialized snail-eaters. Maximum parsimony phylogenetic analysis of a 173 morphological character dataset, with a molecular scaffold enforced, placed Ma.? wentworthi within Dasyuromorphia, in a basal polytomy with Dasyuridae and Mutpuracinus archibaldi, to the exclusion of Barinya wangala, Myrmecobiidae and Thylacinidae. Bayesian analysis of a total evidence dataset that combined morphological with nuclear and mitochondrial DNA sequence data places Ma.? wentworthi as a sister taxon to crown-clade Dasyuridae, although support for this relationship is weak.
... The most primitive form of dental morphology in mammals is tribospheny, which already appeared during Jurassic and is present in both therians and monotremes (Davis, 2011). Starting from this morphology (dilambdodonty), mammalian dentition is either complicated or simplified by the addition or reduction of cusps resulting from changes in the hypocone and/or metacone or paracone, reduction and/or disappearance (zalambdodonty) being much less frequent (Asher and Sánchez-Villagra, 2005). The dental anatomy of tenrecids is particularly useful as they are unique due to the morphology of their dentition. ...
... The solenodontids Solenodon cubanus Peters and Solenodon paradoxus Brandt are ruled out due to their more developed talon; the former species is also ruled out due to the V-shape of the buccal face of the tooth, and the latter due to its more developed talon and buccal cusps (Asher and Sánchez-Villagra, 2005;Wible, 2008). ...
... The marsupial Notoryctes typhlops Stirling can be ruled out due to its wide tooth and its well-developed protocone, the meridiolestid genus Necrolestes due to the absence of a protocone and its narrow tooth, and lastly the marsupial Yalkaparidon due to the absence of a protocone (Archer et al., 1988;Asher and Sánchez-Villagra, 2005). ...
... A functional analogue for spalacotheriid molars are the molars of certain extant tenrecs such as Setifer or Tenrec which have been studied by Schwermann (2014). Tenrecs are placental mammals (afrotherians) with zalambdodont molars that have secondarily lost the protocone and other cusps on the uppers, and reduced the talonid to a single cusp at the lowers ( Fig. 10.10); this way the molars (especially the uppers) resemble the pretribosphenic morphology of cladotherians such as dryolestidans (Asher & Sánchez-Villagra 2005) but also of trechnotherian spalacotheriids (the term pretribosphenic is here used for molars with acute angulation of main cusps and lacking a protocone). In upper molars of Setifer the trigon comprises the lingually placed paracone and the buccally situated stylocone and meta- A B C mesial buccal style, with the mesial paracrista and distal postparacrista as connecting shear-cutting edges ( Fig. 10.11). ...
... The affinities of Nesophontes have been diversely treated in the century since the discovery of the first member of the genus (Anthony, 1916). Most authors have favored a close relationship to soricoids, usually on the basis of an apparently shared pattern of molar dilambdodonty (e.g., Saban, 1954;Van Valen, 1967), but others have discussed whether Nesophontes might instead be the sister taxon of Solenodon, another lipotyphlan restricted to the Caribbean but exhibiting molars that are morphologically zalambdodont (e.g., Gregory, 1920;McDowell, 1958;Asher and Sánchez-Villagra, 2005). This dispute was recently settled in favor of the latter hypothesis, on the basis of ancient DNA evidence collected from a 750 year old N. paramicrus specimen from Hispaniola (Brace et al., 2016). ...
... The affinities of Nesophontes have been diversely treated in the century since the discovery of the first member of the genus (Anthony, 1916). Most authors have favored a close relationship to soricoids, usually on the basis of an apparently shared pattern of molar dilambdodonty (e.g., Saban, 1954;Van Valen, 1967), but others have discussed whether Nesophontes might instead be the sister taxon of Solenodon, another lipotyphlan restricted to the Caribbean but exhibiting molars that are morphologically zalambdodont (e.g., Gregory, 1920;McDowell, 1958;Asher and Sánchez-Villagra, 2005). This dispute was recently settled in favor of the latter hypothesis, on the basis of ancient DNA evidence collected from a 750 year old N. paramicrus specimen from Hispaniola (Brace et al., 2016). ...
Abundant fossils of nesophontid lipotyphlan insectivores and capromyid rodents have been collected from late Quaternary deposits on the Cayman Islands, an island group separated by a major marine barrier from other Caribbean landmasses and isolated from anthropogenic impacts until the arrival of Columbus in 1503 CE. These collections have not previously been formally described. Using morphological and ancient DNA approaches, we document three new taxa of extinct endemic terrestrial mammals from this island group: Nesophontes hemicingulus (Grand Cayman and Cayman Brac), Capromys pilorides lewisi (Grand Cayman, Little Cayman, and Cayman Brac), and Geocapromys caymanensis (Grand Cayman and Cayman Brac). Morphometric comparisons with other extinct and living West Indian mammals indicate that the biogeographic origins of all three new taxa are from source populations on Cuba. Ancient DNA data indicate very low sequence divergence of Capromys pilorides lewisi from mainland Cuban C. pilorides (only 0.5% across the entire mitogenome). Using probabilistic analysis of existing and new radiometric dates, we calculate an estimated extinction date of 1700 CE (95% confidence interval = 1632-1774 CE) for the Cayman Brac Capromys population. This result suggests that at least one endemic Cayman terrestrial mammal population survived for well over a century following first European arrival in the Cayman Islands. The West Indies lost nearly all its species-rich late Quaternary land mammal fauna during the late Holocene due to direct or indirect human impacts, and this study provides a new baseline to understand the magnitude of human-caused mammal extinctions during the recent past.
... The duct of the latter ends at the base of a deeply grooved lower second incisor, which is the source of the generic name (from the Greek "solen" and "odon" for "channel" and "tooth"). Numerous contributions have addressed aspects of the cranial anatomy of S. paradoxus, including osteology (e.g., McDowell 1958;Wible 2008), dentition (e.g., Thenius 1989;Asher and Sánchez-Villagra 2005), myology (e.g., Allen 1910;Whidden 2002), embryology (e.g., MacPhee 1981), and brain anatomy (e.g., Boller 1969;Orihuela 2014). Moreover, craniodental features long have factored in discussions of the systematic placement of S. paradoxus and its close relative from Cuba, S. cubanus Peters, 1861(e.g., Gregory 1910Mc-Dowell 1958;Ottenwalder 2001). ...
The osseous elements of the foot and ankle are described and illustrated in detail for the Hispaniolan solenodon, Solenodon paradoxus Brandt, 1833, one of two extant species of the lipotyphlan family Solenodontidae. Comparisons are made with the same elements in representatives of the three remaining extant families of lipotyphlans, the soricid Crocidura luna Dollman, 1910, the talpid Parascalops breweri (Bachman, 1842), and the erinaceid Erinaceus europaeus Linnaeus, 1758. The muscles attaching to the osseous elements of the foot in lipotyphlans are summarized based on the literature. The solenodon foot is generalized but with a unique modification regarding the entocuneiform: it has an elongate medial spur with a sizeable facet for the astragalar head. The other lipotyphlans studied have a medial spur of the entocuneiform, but it is well separated from the astragalus by the navicular. Crocidura luna also has a remarkable modification; the ectal facets on the astragalus and calcaneus have opposing concavoconvex surfaces. Measurements of all osseous elements of the foot were collected in the four lipotyphlans studied here. Various indices, the vast majority of which were taken from the literature, were calculated from these measurements. Metrical data were combined with those from prior studies that included relevant pedal measurements of lipotyphlans and some clades outside of Lipotyphla. Two Principal Components Analyses were performed to illustrate our data with regard to those of prior studies.
... For example, wear on tightly locking shearing crests in carnivores helps maintain their sharpness [83], which combined with carnassial rotation in which the tooth's orientation changes as the occlusal surfaces on the blades wear [109] can maintain a precise shearing function even as the tooth crown is abraded. Zalambdodont dentitions, which have interlocking v-shaped teeth, typically require less occlusal precision than the complex interdigitizing shearing blades of tribosphenic teeth [110]. ...
Our understanding of the evolution of the dentition has been transformed by advances in the developmental biology, genetics, and functional morphology of teeth, as well as the methods available for studying tooth form and function. The hierarchical complexity of dental developmental genetics combined with dynamic effects of cells and tissues during development allow for substantial, rapid, and potentially non-linear evolutionary changes. Studies of selection on tooth function in the wild and evolutionary functional comparisons both suggest that tooth function and adaptation to diets are the most important factors guiding the evolution of teeth, yet selection against random changes that produce malocclusions (selectional drift) may be an equally important factor in groups with tribosphenic dentitions. These advances are critically reviewed here.
... An example of such a bias can be found in their treatment of zalambdodonty in Necrolestes. Zalambdodont mammals have high crested, "lambda"-shaped molars, where the primary lingual cusp is not the protocone, as seen in most tribosphenic taxa, but either the paracone or metacone (Asher and Sánchez-Villagra 2005). In most zalambdodont eutherians, such as tenrecs, the primary lingual cusp is inferred to be the paracone based on its occlusion in the hypoflexid of the corresponding lower molar. ...
... In most zalambdodont eutherians, such as tenrecs, the primary lingual cusp is inferred to be the paracone based on its occlusion in the hypoflexid of the corresponding lower molar. Further evidence for this is provided by the tenrec Potamogale which retains both a small metacone and a large paracone (Asher and Sánchez-Villagra 2005). Molecular phylogenies resolve Potamogalinae as the sister-group to all other tenrecs (Asher et al. 2010) providing independent support for paracone zalambdodonty in the wider clade. ...
... In a review of the dentally zalambdodont Mammalia, Asher and Sánchez-Villagra (2005) suggested that the occlusal pattern of Necrolestes supported the identification of the primary lingual cusp as a metacone. They based this claim on YPM-PU 15699, a skull of Necrolestes that preserves upper and lower teeth in occlusion. ...
The enigmatic mammal Necrolestes patagonensis from the Miocene of Patagonia possesses a highly apomorphic osteological form that has confounded phylogenetic interpretation for over a century. In this time it has been affiliated with both eutherians and metatherians; however, a recent study by Rougier et al. (Proc Natl Acad Sci USA 109:19871–19872, 2012) raises the intriguing possibility that Necrolestes is a relictual member of a clade of South American non-therian dryolestoids, the Meridiolestida. This group is known chiefly from the Cretaceous of South America and assignment of Necrolestes to Meridiolestida implies a ghost lineage of about 40 million years. Such a lengthy ghost lineage requires strong evidence, which minimizes potentially circular assumptions of anatomical homology. Here, we vary the coding of cusp
homologies in Necrolestes, previously assumed to diverge from the metatherian pattern, and add zalambdodont and incipiently zalambdodont metatherian taxa to the analyses, in order to assess the effects of non-independent characters and taxon sampling on the original topology. The results of both maximum parsimony and Bayesian analysis using the Mk model show that these possible sources of bias have little
effect on the topology and ultimately increase confidence in the placement of Necrolestes in Meridiolestida and its concomitant 40 million year ghost lineage. Additionally, our Bayesian analysis resolves Australosphenida in a trichotomy with Peramus and Vincelestes+ Boreosphenida. This contrasts with the majority of existing topologies, and raises interesting questions regarding both the evolution of tribospheny and the use of the Mk model with paleontological datasets.
