New Specimen of CF. Asiatosuchus (Crocodyloidea) from the Middle Eocene Drazinda Formation of the Sulaiman Range, Punjab (Pakistan)

163-189http://deepblue.lib.umich.edu/bitstream/2027.42/48655/2/ID522.pd

Antiquity of forelimb ecomorphological diversity in the mammalian stem lineage (Synapsida)

Mammals and their closest fossil relatives are unique among tetrapods in expressing a high degree of pectoral girdle and forelimb functional diversity associated with fully pelagic, cursorial, subterranean, volant, and other lifestyles. However, the earliest members of the mammalian stem lineage, the “pelycosaur”-grade synapsids, present a far more limited range of morphologies and inferred functions. The more crownward nonmammaliaform therapsids display novel forelimb morphologies that have been linked to expanded functional diversity, suggesting that the roots of this quintessentially mammalian phenotype can be traced to the pelycosaur–therapsid transition in the Permian period. We quantified morphological disparity of the humerus in pelycosaur-grade synapsids and therapsids using geometric morphometrics. We found that disparity begins to increase concurrently with the emergence of Therapsida, and that it continues to rise until the Permo-Triassic mass extinction. Further, therapsid exploration of new regions of morphospace is correlated with the evolution of novel ecomorphologies, some of which are characterized by changes to overall limb morphology. This evolutionary pattern confirms that nonmammaliaform therapsid forelimbs underwent ecomorphological diversification throughout the Permian, with functional elaboration initially being more strongly expressed in the proximal end of the humerus than the distal end. The role of the forelimbs in the functional diversification of therapsids foreshadows the deployment of forelimb morphofunctional diversity in the evolutionary radiation of mammals

Modeling The Role Of Primary Productivity Disruption In End-Permian Extinctions, Karoo Basin, South Africa

The end-Permian mass extinction is well-known as the most severe mass extinction of the Phanerozoic. Terrestrial communities appear to have been strongly affected by the event, but the cause of the extinction remains enigmatic. Here we explore whether primary producer disruption (e.g., extinction of terrestrial plants) could have led to a collapse of end-Permian terrestrial ecosystems, using models of probabilistic trophic networks. Based on a trophic network reconstructed for the Dicynodon Assemblage Zone community of the Karoo Basin, we show that late Permian terrestrial communities were vulnerable to collapse brought about by the disruption of primary producers. However, relatively high levels of primary producer loss are needed to account for observed levels of extinction among consumers in the Dicynodon zone fauna. Depending on network parameters, we predict that a shutdown of 69% to 87% of primary producers would be needed to generate observed extinction levels. A disruption of this magnitude is not unreasonable, given that terrestrial floras underwent a major turnover at the end of the Permian, and our predictions can be tested by further scrutiny of floras from this time

Redescription of Digalodon rubidgei, an emydopoid dicynodont (Therapsida, Anomodontia) from the Late Permian of South Africa

The Late Permian dicynodont Digalodon rubidgei Broom and Robinson, 1948, is redescribed based on reanalysis of the holotype and newly recognized referable specimens. Digalodon can be diagnosed by the presence of a long "beak" sharply demarcated from the caniniform process; an extremely tall zygomatic ramus of the squamosal, with a thickened, "folded-over" dorsal margin; raised parietal "lips" along the lateral edges of the pineal foramen; and a broad posterolateral expansion of the parietal, excluding the postorbital from the back of the skull roof. Inclusion of Digalodon in a recent analysis of anomodont phylogeny recovers it as a kistecephalian emydopoid, specifically as the sister taxon to the clade containing the remaining kistecephalians. Four definite specimens of Digalodon are known, but several additional specimens lacking tusks, the swollen pineal "lips", and a thickened zygoma may represent sexually dimorphic females or juveniles. Specimens of Digalodon are restricted to the central portion of the Karoo Basin, in the area around Graaff-Reinet, and are part of a characteristic fauna probably representing a limited time span

Trophic Network Models Explain Instability Of Early Triassic Terrestrial Communities

Studies of the end-Permian mass extinction have emphasized potential abiotic causes and their direct biotic effects. Less attention has been devoted to secondary extinctions resulting from ecological crises and the effect of community structure on such extinctions. Here we use a trophic network model that combines topological and dynamic approaches to simulate disruptions of primary productivity in palaeocommunities. We apply the model to Permian and Triassic communities of the Karoo Basin, South Africa, and show that while Permian communities bear no evidence of being especially susceptible to extinction, Early Triassic communities appear to have been inherently less stable. Much of the instability results from the faster post-extinction diversification of amphibian guilds relative to amniotes. The resulting communities differed fundamentally in structure from their Permian predecessors. Additionally, our results imply that changing community structures over time may explain long-term trends like declining rates of Phanerozoic background extinction

Do Bony Orbit Dimensions Predict Diel Activity Pattern In Sciurid Rodents?

Diel activity pattern (DAP) is a key aspect of an animal\u27s ecology, but it is difficult to infer when behavior cannot be directly observed, as in the fossil record. Various anatomical correlates have therefore been used to attempt to classify DAP. Eyeball dimensions are good predictors of DAP because they relate directly to light sensitivity of the eye. Osteological characters, such as scleral ring dimensions, are also reliable proxies, but bony orbit dimensions alone have proven less reliable because soft tissues other than the eyeball can affect orbit size and shape. However, it would be useful if bony orbit dimensions could be used to determine DAP, particularly for mammals, which have no scleral ring, and nonmammalian synapsids, which infrequently preserve scleral rings. We investigated the possibility of predicting DAP in sciurids (Mammalia: Rodentia: Sciuridae) using orbit measurements and other cranial dimensions, and a variety of quantitative methods, including phylogenetic flexible discriminant analysis, classification trees, and logistic regression. The latter two methods do not require a priori assignment of DAP and therefore reflect the situation in a fossil data set. We find that although there are some interfering phylogenetic factors, nocturnal and non‐nocturnal sciurids can be differentiated from one another with over 80% accuracy using all methods investigated here; attempts to differentiate crepuscular animals from nocturnal and diurnal species proved much less successful. Our results indicate that these analyses offer several viable options for predicting DAP in the fossil record, but such analyses should be conducted in a phylogenetic context whenever possible. Anat Rec, 301:1774–1787, 2018

A new eutherocephalian (Therapsida, Therocephalia) from the upper Permian Madumabisa Mudstone Formation (Luangwa Basin) of Zambia

<div><p>ABSTRACT</p><p>A new therocephalian therapsid, <i>Ichibengops munyamadziensis</i>, gen. et sp. nov., is described on the basis of two partial skulls from the upper Permian (Wuchiapingian) upper Madumabisa Mudstone Formation of the Luangwa Basin, Zambia. The specimens offer insights into the diversity of therocephalians in a poorly sampled region, preserving unique maxillary structures, dental morphology that is intermediate between basal therocephalians and eutherocephalians, and a maxillovomerine bridge forming an incipient secondary palate. A phylogenetic analysis of 135 craniodental and postcranial characters from 56 therapsid taxa (including 49 therocephalians) recovered <i>I. munyamadziensis</i> as the sister taxon of the Russian <i>Chthonosaurus</i>, with both taxa resolving near the hofmeyriid + whaitsiid + baurioid clade (either as the sister group to this clade or nested near whaitsiids). <i>Ichibengops</i> shares with <i>Chthonosaurus</i> several features, including a ventral maxillary flange in which the upper postcanines are situated (also in <i>Lycosuchus</i>), anteroposteriorly short suborbital vacuities with strongly scalloped anterior borders, a furrowed or ridged surface texture on the palatal surface of the palatine, and a possible maxillovomerine bridge (although this latter structure is incompletely preserved in <i>Chthonosaurus</i>). The new taxon, along with its proposed relationship to <i>Chthonosaurus</i>, adds to a list of sister-group pairs of Wuchiapingian tetrapods in southern Gondwana and Laurasia, indicating that effective, though largely unknown, dispersal routes persisted in Pangea at least through early late Permian times.</p><p>http://zoobank.org/urn:lsid:zoobank.org:pub:3C00620E-64B4-4CF0-BFAD-0336AE7C8196</p><p>SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP</p></div

Abnormal development of paired enigmatic structures in the derived dicynodont Lystrosaurus murrayi (Therapsida, Anomodontia)

Derived dicynodonts, including Lystrosaurus murrayi, have edentulous lower jaws. As an interesting exception to this conventional wisdom, a well-preserved specimen of L. murrayi (MGGC-8850/1RE13 F) has abnormal, paired mandibular structures similar in overall morphology to dental teeth. The specimen pertains to the historical collections of the Museo G. Capellini (Bologna, Italy) and was collected in 1929 by M. Gortani during prospecting activities near Harrismith, South Africa. The specimen is articulated and includes a nearly complete skull, the first eight vertebrae and the proximal end of the right scapula. Reconstruction based on a Dual-Beam CT revealed unusual, paired structures similar to mandibular teeth, encased within the lower jaw, lingual to maxillary tusks. Different interpretations are possible for the abnormal mandibular structures in MGGC-8850/1RE13 F: 1) the dental lamina in the lower jaw, which would normally degenerate in derived dicynodonts, remained active and potentiated the odontogenesis; 2) the dental lamina was potent in the lower jaw throughout the ontogeny across dicynodonts but activated differentially; or 3) the mandibular patterning in our specimen was dorsalized, which resulted in an ectopic formation of upper jaw dentition in the lower jaws. Supranumerary or ectopic teeth are a commonly screened phenotype in modern mammalian models. Such variation distributes in a continuum – rarely does an edentulous jaw develop fully functional teeth that are present in outgroups. The absence of mandibular dentition in other specimens of L. murrayi and in most other bidentalian dicynodonts suggests that MGGC-8850/1RE13 F represents a rare developmental abnormality or a case of atavism

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Nexus file containing time-callibrated phylogen