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1. A new tusked cistecephalid dicynodont (Therapsida, Anomodontia) from the upper Permian upper Madumabisa Mudstone Formation, Luangwa Basin, Zambia

   https://doi.org/10.1002/spp2.1285  

   Angielczyk, Kenneth D. ; Benoit, Julien ; Rubidge, Bruce S. ; Ruta, ed., Marcello ( October 2019 , Papers in Palaeontology)

   Cistecephalids are among the most distinctive Permian dicynodonts because of their highly derived skulls and postcrania, which indicate a fossorial ecology. Four cistecephalid species have been described from India, South Africa, and Tanzania; a fifth putative species has been reported from the Luangwa Basin of Zambia but never formally described. Here we present a detailed description of the Luangwa Basin cistecephalid, which we nameKembawacela kitchingigen. et. sp. nov. The most obvious diagnostic character ofK. kitchingiis the presence of caniniform tusks in most specimens. Other important characters include a pineal foramen located at the posterior end of the skull roof; an interparietal that has a pair of anterior processes that extend onto the dorsal surface of the skull, flanking the pineal foramen (but otherwise is restricted to the occipital surface); an undivided nuchal crest; and a trough on the ventral surface of the mid‐ventral vomerine plate. Phylogenetic analysis reconstructsKembawacelaas a basal cistecephalid and confirms that Cistecephalidae is a well‐supported clade. However, relationships within the clade received low branch support. Increased knowledge of cistecephalid diversity shows that they vary in functionally relevant characters, such as degree of inflation of the bony vestibule and the morphology of the scapula and humerus, indicating the need for a more nuanced approach to the relationship between form, function and ecology in the clade. The highly allopatric distribution of cistecephalid species suggests that they experienced strong interspecific competition for limited resources and had limited dispersal ability, similar to extant subterranean mammals.

    

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2. Developmental origins of the crocodylian skull table and platyrostral face

   https://doi.org/10.1002/ar.24802  

   Morris, Zachary S. ; Vliet, Kent A. ; Abzhanov, Arhat ; Pierce, Stephanie E. ( October 2021 , The Anatomical Record)

   The dorsoventrally flattened skull typifies extant Crocodylia perhaps more than any other anatomical feature and is generally considered an adaptation for semi‐aquatic feeding. Although the evolutionary origins of caniofacial flattening have been extensively studied, the developmental origins have yet to be explored. To understand how the skull table and platyrostral snout develop, we quantified embryonic development and post‐hatching growth (ontogeny) of the crocodylian skull in lateral view using geometric morphometrics. Our dataset (n = 103) includes all but one extant genus and all of the major ecomorphs, including the extremely slender‐snoutedGavialisandTomistoma. Our analysis reveals that the embryonic development of the flattened skull is remarkably similar across ecomorphs, including the presence of a conserved initial embryonic skull shape, similar to prior analysis of dorsal snout shape. Although differences during posthatching ontogeny are recovered among ecomorphs, embryonic patterns are not distinct, revealing an important shift in developmental rate near hatching. In particular, the flattened skull table is achieved by the end of embryonic development with no changes after hatching. Further, the rotation of skull roof and facial bones during development is critical for the stereotypical flatness of the crocodylian skull. Our results suggest selection on hatchling performance and constraints on embryonic skull shape may have been important in this pattern of developmental conservation. The appearance of aspects of cranial flatness among Jurassic stem crocodylians suggests key aspects of these cranial developmental patterns may have been conserved for over 200 million years.

    

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3. Updated cranial and mandibular description of the Late Cretaceous (Maastrichtian) baenid turtle Saxochelys gilberti based on micro-computed tomography scans and new information on the holotype-shell association

   https://doi.org/10.1186/s13358-023-00301-6  

   Spicher, Gaël E. ; Lyson, Tyler R. ; Evers, Serjoscha W. ( January 2024 , Swiss Journal of Palaeontology)

   Saxochelys gilbertiis a baenid turtle from the Late Cretaceous Hell Creek Formation of the United States of America known from cranial, shell, and other postcranial material. Baenid turtles are taxonomically diverse and common fossil elements within Late Cretaceous through Eocene faunas. Detailed anatomical knowledge is critical to understanding the systematics and morphological evolution of the group. This is particularly important as baenids represent an important group of continental vertebrates that survived the mass extinction event associated with the Cretaceous/Paleogene boundary. High-resolution micro-computed tomography scanning of the holotype skull reveals additional anatomical details for the already well-knownSaxochelys gilberti. This includes the revision of some anatomical statements from the original description, but also detailed knowledge on internal anatomical features of the braincase and the description of a well-preserved axis (cervical vertebra 2). Our new detailed description and previous work on the shell and postcrania makeSaxochelysone of the best-described, nearly complete baenid turtles, which are often only known from either isolated shell or cranial material. A revised phylogenetic analysis confirms the position ofSaxochelys gilbertias a derived baenid (Eubaeninae) more closely related toBaena arenosathan toEubaena cephalica.

    

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4. Biomechanical performance of the cranio‐mandibular complex of the small notosuchian Araripesuchus gomesii (Notosuchia, Uruguaysuchidae)

   https://doi.org/10.1002/ar.24697  

   Nieto, Mauro N. ; Degrange, Federico J. ; Sellers, Kaleb C. ; Pol, Diego ; Holliday, Casey M. ( June 2021 , The Anatomical Record)

   Notosuchia is a clade of crocodyliforms that was highly successful and diverse in the Cretaceous of Gondwana.Araripesuchus gomesiiis a small notosuchian from the Early Cretaceous of Brazil that belongs to Uruguaysuchidae, one of the subgroups of notosuchians that first radiated, during the Aptian–Albian. Here we present a finite element analysis ofA. gomesiibased on a model reconstructed from CT scans and performed using published bone properties for crocodiles. The adductor musculature and their respective attachment areas were reconstructed based on Extant Phylogenetic Bracket. Different functional scenarios were tested applying an estimated 158 N bite force: unilateral bite, bilateral bite, pullback, head‐shake, and head‐twist. The results obtained were compared with those ofAlligator mississippiensis, one of its closest living relatives. In the different simulations, the skull and lower jaws ofAraripesuchussuffers more stress in the head‐shake movement, followed by the unilateral and pullback bites with stress focalized in the premaxillary region. In contrast, the head‐twist is the one with smaller stress values.Araripesuchuspossess an oreinirostral skull that may provide greater overall resistance in the different scenarios on average, unlikeAlligatorthat has a platyrostral skull with less resistance to dorsoventral mechanical loads. Previous hypotheses that consideredA. gomesiias omnivorous coupled with our results, its small size, and likely limited bite force, suggest this taxon probably fed on small prey and other trophic items that could catch and handle entirely with its mouth, such as insects and small vertebrates.

    

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5. Virtual endocranial and inner ear endocasts of the Paleocene ‘condylarth’ Chriacus : new insight into the neurosensory system and evolution of early placental mammals

   https://doi.org/10.1111/joa.13084  

   Bertrand, Ornella C. ; Shelley, Sarah L. ; Wible, John R. ; Williamson, Thomas E. ; Holbrook, Luke T. ; Chester, Stephen G. B. ; Butler, Ian B. ; Brusatte, Stephen L. ( October 2019 , Journal of Anatomy)

   The end‐Cretaceous mass extinction allowed placental mammals to diversify ecologically and taxonomically as they filled ecological niches once occupied by non‐avian dinosaurs and more basal mammals. Little is known, however, about how the neurosensory systems of mammals changed after the extinction, and what role these systems played in mammalian diversification. We here use high‐resolution computed tomography (CT) scanning to describe the endocranial and inner ear endocasts of two species,Chriacus pelvidensandChriacus baldwini, which belong to a cluster of ‘archaic’ placental mammals called ‘arctocyonid condylarths’ that thrived during theca. 10 million years after the extinction (the Paleocene Epoch), but whose relationships to extant placentals are poorly understood. The endocasts provide new insight into the paleobiology of the long‐mysterious ‘arctocyonids’, and suggest thatChriacuswas an animal with anencephalization quotient (EQ)range of 0.12–0.41, which probably relied more on its sense of smell than vision, because the olfactory bulbs are proportionally large but the neocortex and petrosal lobules are less developed. Agility scores, estimated from the dimensions of the semicircular canals of the inner ear, indicate thatChriacuswas slow to moderately agile, and its hearing capabilities, estimated from cochlear dimensions, suggest similarities with the extant aardvark.Chriacusshares many brain features with other Paleocene mammals, such as a small lissencephalic brain, large olfactory bulbs and small petrosal lobules, which are likely plesiomorphic for Placentalia. The inner ear ofChriacusalso shares derived characteristics of the elliptical and spherical recesses with extinct species that belong to Euungulata, the extant placental group that includes artiodactyls and perissodactyls. This lends key evidence to the hypothesized close relationship betweenChriacusand the extant ungulate groups, and demonstrates that neurosensory features can provide important insight into both the paleobiology and relationships of early placental mammals.

    

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