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[dinosaur] Mesosuchus (Rhynchosauria) braincase + dental microwear in lepidosaurs (free pdfs)

Ben Creisler

New free non-dino papers:

Gabriela Sobral & Johannes MÃller (2019)
The braincase of Mesosuchus browni (Reptilia, Archosauromorpha) with information on the inner ear and description of a pneumatic sinus.
PeerJ 7:e6798
doi: https://doi.org/10.7717/peerj.6798

Free pdf:

Rhynchosauria is a group of archosauromorph reptiles abundant in terrestrial ecosystems of the Middle Triassic. Mesosuchus is one of the earliest and basalmost rhynchosaurs, playing an important role not only for the understanding of the evolution of the group as a whole, but also of archosauromorphs in general. The braincase of Mesosuchus has been previously described, albeit not in detail, and the middle and inner ears were missing. Here, we provide new information based on micro-computed tomography scanning of the best-preserved specimen of Mesosuchus, SAM-PK-6536. Contrary to what has been stated previously, the braincase of Mesosuchus is dorso-ventrally tall. The trigeminal foramen lies in a deep recess on the prootic whose flat ventral rim could indicate the articulation surface to the laterosphenoid, although no such element was found. The middle ear of Mesosuchus shows a small and deeply recessed fenestra ovalis, with the right stapes preserved in situ. It has a rather stout, imperforated and posteriorly directed shaft with a small footplate. These features suggest that the ear of Mesosuchus was well-suited for the detection of low-frequency sounds. The semicircular canals are slender and elongate and the floccular fossa is well-developed. This is indicative of a refined mechanism for gaze stabilization, which is usually related to non-sprawling postures. The most striking feature of the Mesosuchus braincase is, however, the presence of a pneumatic sinus in the basal tubera. The sinus is identified as originating from the pharyngotympanic system, implying ossified Eustachian tubes. Braincase pneumatization has not yet been a recognized feature of stem-archosaurs, but the potential presence of pneumatic foramina in an array of taxa, recognized here as such for the first time, suggests braincase sinuses could be present in many other archosauromorphs.


Daniela E. Winkler, Ellen Schulz-Kornas, Thomas M. Kaiser Âand Thomas TÃtken (2019)
Dental microwear texture reflects dietary tendencies in extant Lepidosauria despite their limited use of oral food processing.
Proceedings of the Royal Society B 286: 20190544.
doi: https://doi.org/10.1098/rspb.2019.0544

Free pdf:

Lepidosauria show a large diversity in dietary adaptations, both among extant and extinct tetrapods. Unlike mammals, Lepidosauria do not engage in sophisticated mastication of their food and most species have continuous tooth replacement, further reducing the wear of individual teeth. However, dietary tendency estimation of extinct lepidosaurs usually rely on tooth shape and body size, which allows only for broad distinction between faunivores and herbivores. Microscopic wear features on teeth have long been successfully applied to reconstruct the diet of mammals and allow for subtle discrimination of feeding strategies and food abrasiveness. Here, we present, to our knowledge, the first detailed analysis of dental microwear texture on extant lepidosaurs using a combination of 46 surface texture parameters to establish a framework for dietary tendency estimation of fossil reptilian taxa. We measured dental surface textures of 77 specimens, belonging to herbivorous, algaevorous, frugivorous, carnivorous, ovivorous, insectivorous, molluscivorous, as well as omnivorous species. Carnivores show low density and shallow depth of furrows, whereas frugivores are characterized by the highest density of furrows. Molluscivores show the deepest wear features and highest roughness, herbivores have lower surface roughness and shallower furrows compared to insectivores and omnivores, which overlap in all parameters. Our study shows that despite short foodâtooth interaction, dental surface texture parameters enable discrimination of several feeding strategies in lepidosaurs. This result opens new research avenues to assess diet in a broad variety of extant and extinct non-mammalian taxa including dinosaurs and early synapsids.

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