First record of a basal mammaliamorph from the early Late Triassic Ischigualasto Formation of Argentina

PloS One
Rachel V S WallaceTimothy Rowe

Abstract

We describe a new probainognathian cynodont, Pseudotherium argentinus, from the early Late Triassic Ischigualasto Formation of Argentina. Pseudotherium adds to a growing assemblage of small Triassic cynodonts that offers new insight into events leading up to the origin of crown Mammalia and the successively more inclusive Mammaliaformes and Mammaliamorpha. Using high-resolution X-ray computed tomography, we illustrate and describe the holotype and only known specimen, which consists of a well-preserved isolated skull. It preserves apomorphic features of the orbit and braincase. Prefrontal and vestigial postorbital bones are present, despite the absence of an ossified postorbital bar. As in Brasilitherium riograndensis, thin turbinal-like bones are present in the nasopharyngeal passage, and we discuss impediments to establishing their identity and function. Compared to more basal cynodonts, the cochlea is elongated but uncoiled and in this and other features it resembles basal mammaliamorphs. Our analysis found weak support for Pseudotherium as the sister taxon of Tritylodontidae. However, a broader assessment of its relationships in light of additional character data from the literature and unpublished computed tomography data ...Continue Reading

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Citations

May 18, 2021·Frontiers in Cellular Neuroscience·Gordon M ShepherdCharles A Greer
Nov 16, 2021·The Anatomical Record : Advances in Integrative Anatomy and Evolutionary Biology·Leonardo KerberFlávio A Pretto

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Methods Mentioned

BETA
X-ray

Software Mentioned

PubMed
PAUP
Adobe Photoshop
Adobe Illustrator
VGStudio
Phong
Xradia
Probainognathus
LOCKSS
DELTRANS

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