Probelesodon sanjuanensis is a member of Eucynodontia, a lineage that includes mammals and their closest extinct relatives. As with the other eucynodonts (Probainognathus, Exaeretodon, and Ecteninion) and the oldest-known dinosaurs (Eoraptor and Herrerasaurus) featured on this site, Probelesodon was collected from the late Triassic sediments of Argentina.

Eucynodontia is diagnosed by a number of craniodental advances that are adaptations for a more complex mastication system. Probelesodon, like other eucynodonts, possesses a mosaic of primitive and advanced characters. It is similar to mammals in the possession of a well-developed, posteriorly-extended palate, a double occipitial condyle, and the loss of the pineal foramen. Primitive characters found in Probelesodon include the presence of the postorbital and prefrontal bones, the presence of a postorbital bar, and a quadrate-articular jaw articulation. Within Eucynodontia, Probelesodon is the sister taxon to Chiniquodon. Like Probainognathus and Ecteninion, it is carnivorous and possesses recurved, multicuspid cheek teeth.

This specimen, the holotype, was collected from the Upper Triassic Ischigualasto Formation of the San Juan Province of northwestern Argentina. The specimen was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Oscar Alcober of the Museo de Ciencias Naturales, and Dr. William Sill of the Universidad Nacional de San Juan, Argentina. Funding was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of The University of Texas at Austin.

The specimen was scanned by Matthew Colbert and Richard Ketcham on 13 January 2000 along the coronal axis for a total of 400 slices, each slice 0.292 mm thick, with an interslice spacing of 0.2188 mm (for a slice overlap of 0.0732 mm).

Literature

Gauthier, J., A. G. Kluge, and T. Rowe. 1988. Amniote phylogeny and the importance of fossils. Cladistics 4:105-209.

Kemp, T. S. 1982. Mammal-like Reptiles and the Origin of Mammals. Academic Press, London.

Martinez, R., and C. Forster. 1996. The skull of Probelesodon sanjuanensis, sp. nov., from the late Triassic Ischigualasto Fm. of Argentina. Journal of Vertebrate Paleontology 16:285-291.

Rogers, R. R., C. C. Swisher III, P. C. Sereno, A. M. Monetta, C. A. Forster, and R. N. Martinez. 1993. The Ischigualasto tetrapod assemblage (Late Triassic, Argentina) and ⁴⁰Ar/³⁹Ar dating of dinosaur origins. Science 260:794-797.

Romer, A. S. 1969. The Chañares (Argentina) Triassic Reptile Fauna V. A new chiniquodontid cynodont, Probelesodon lewisi - cynodont ancestry. Breviora 333:1-24.

Rowe, T. 1988. Definition, diagnosis and origin of Mammalia. Journal of Vertebrate Paleontology 8:241-264.

Rowe, T. 1993. Phylogenetic systematics and the early history of mammals; pp. 129-145 in F. S. Szalay, M. J. Novacek, and M. C. McKenna (eds.), Mammalian Phylogeny. Springer-Verlag, New York.

Rowe, T., W. Carlson, and W. Bottorff. 1995. Thrinaxodon: Digital Atlas of the Skull. CD-ROM (Second Edition, for Windows and Macintosh platforms), University of Texas Press, 547 megabytes.

Sues, H. D. 1985. The relationships of the Tritylodontidae (Synapsida). Zoological Journal of the Linnean Society 85:205-218.

None available.