Anisodontosaurus

Anisodontosaurus is an extinct genus of trilophosaurid allokotosaur known from the Middle Triassic Moenkopi Formation of Arizona.^[1] The type species, A. greeri, was named and described by Samuel Paul Welles in 1947.^[1]

Anisodontosaurus Temporal range: Middle Triassic, 247.2–242.0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Holotype jaw
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauromorpha
Clade:	†Allokotosauria
Order:	†Trilophosauria
Family:	†Trilophosauridae (?)
Genus:	†Anisodontosaurus Welles, 1947
Species:	†A. greeri
Binomial name
†Anisodontosaurus greeri Welles, 1947

Discovery and naming

The holotype, a jaw catalogued as UCMP V3922, was discovered in 1940 and was described seven years later.^[1]

Apart from the type specimen, Anisodontosaurus is known from the referred specimen UCMP 37815, a right ilium.^[2][3]

Classification

Its taxonomic placement was largely unknown (it was placed within the Eosuchia by Welles in 1947)^[1] until the holotype was reassessed in 1998, when it was recovered as a lepidosauromorph or a trilophosaurid.^[4]

A 2023 redescription of available fossils supported its identification as a trilophosaurid, specifically as the sister taxon to Variodens, from the Late Triassic of the United Kingdom. The clade containing Anisodontosaurus and Variodens is the longest-lasting subset of Trilophosauridae, as Anisodontosaurus is one of the oldest known members of the family while Variodens is among the youngest.^[5]

References

1. S. P. Welles. (1947). Vertebrates from the Upper Moenkopi Formation of northern Arizona. University of California Publications in Geological Sciences 27(7):241-294
2. R. L. Carroll. (1988). Vertebrate Paleontology and Evolution. 1-698
3. S. J. Nesbitt. 2005. The Moenkopi Formation along the Little Colorado River in eastern Arizona. In S. J. Nesbitt, W. G. Parker, R. B. Irmis (eds.), Guidebook to the Triassic Formations of the Colorado Plateau in northern Arizona, Mesa Southwest Museum Bulletin 9:13-23
4. A. P. Hunt, S. G. Lucas, and P. S. Spencer. (1998). A reassessment of the taxonomic affinities of the enigmatic tetrapod Anisodontosaurus greeri Welles 1947 from the Middle Triassic of western North America. Neues Jahrbuch für Geologie und Paläontologie - Monatshefte 1998(4):212-222
5. Foffa, Davide; Nesbitt, Sterling J.; Kligman, Ben T.; Butler, Richard J.; Stocker, Michelle R. (2023-07-24). "New specimen and redescription of Anisodontosaurus greeri (Moenkopi Formation: Middle Triassic) and the spatiotemporal origins of Trilophosauridae". Journal of Vertebrate Paleontology. doi:10.1080/02724634.2023.2220015. ISSN 0272-4634.