This page serves supplemental imagery for a paper entitled First record of a basal mammaliamorph from the Carnian-Norian Ischigualasto Formation of Argentina by R. Wallace, R. Martínez, and T. Rowe (2019, PLoS ONE, 14(8):e0218791). The abstract is as follows:

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 Brasilotherium 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 However, a broader assessment of its relationships in light of additional character data from the literature and unpublished computed tomography data suggest that it may be more realistic to view the relationships of Pseudotherium as an unresolved polytomy with tritylodontids, and the taxa referred to as tritheledontids and brasilodontids (groups of variable membership and questionable monophyly). Thus, Pseudotherium may lie just inside or just outside of Mammaliamorpha, and there is also weak character support for its sister taxon relationship with Brasilitherium. Our results amplify previous conclusions that phylogenetic relationships in this adaptive radiation of small cynodonts will remain somewhat uncertain until more complete specimens are recovered, and until high-resolution CT scans of existing specimens become available to the larger community. Toward that goal, we make the CT dataset for the holotype of Pseudotherium argentinus publically available under a Creative Commons license at www.DigiMorph.org.

Click here to download the original HRXCT data (2.0 Gb).

This specimen, the holotype and only known specimen, was collected from the Late Triassic Ischigualasto Formation in Argentina.

The specimen was made available to The University of Texas High-Resolution X-ray CT Facility for scanning by Cecilia Apaldetti of the Museo y Universidad Nacional de San Juan and Dr. Timothy Rowe of The University of Texas. Funding for scanning was provided by Dr. Rowe.

The specimen was scanned by Jessie Maisano on 11 November 2013 along the coronal axis for a total of 1733 slices. Voxel size is 0.04421 mm.

Click here to download the original HRXCT data (2.0 Gb).

Literature

Wallace, R., Martínez, R., and Rowe, T. 2019. First record of a basal mammaliamorph from the Carnian-Norian Ischigualasto Formation of Argentina. PLoS ONE, 14(8), e0218791.

None available.