Two New Tritylodontids (Synapsida, Cynodontia, Mammaliamorpha) from the Upper Jurassic, Southwestern Mongolia

Abstract

Two new genera and species of Tritylodontidae, Shartegodon altai and Nuurtherium baruunensis, are described and compared with other known tritylodontids. The new taxa are represented by two partial skulls and, in the case of Nuurtherium, postcranial elements. They were collected from the lower part of the Ulan Malgait Sequence (Upper Jurassic) in the Shar Teg locality, Gobi-Altai Aimag, southwestern Mongolia. The upper postcanine teeth of these two genera have unique cusp formulae that differentiate them from other tritylodontids. As has been suggested for most tritylodontids in general, these two new genera may have been herbivorous.

A reassessment of the postcanine dentition and systematics of the tritylodontidStereognathus(Cynodontia, Tritylodontidae, Mammaliamorpha), from the Middle Jurassic of the United Kingdom

“…Phylogenetic Analysis-Trees were analyzed using TNT version 1.5 (Goloboff et al, 2008), and the character matrix of 35 characters and 17 taxa is based on that of Velazco et al (2017), with Stereognathus rescored to reflect our findings (Appendices 1, 2). We used the New Technology search, selecting ratchet, sectorial search, tree drift, and tree fusing.…”

“…Yuanotherium (Hu et al, 2009), Shartegodon (Velazco et al, 2017), and Nuurtherium (Velazco et al, 2017), which all have a higher number of cusps in one or more rows.…”

“…Tritylodontidae currently includes over 17 genera (with at least five more genera debated or synonymized) and have been described from Africa (Owen, 1884;Fourie, 1963), Antarctica (Lewis, 1986;Hammer and Smith, 2008), Asia (Young, 1940(Young, , 1982Chow and Hu, 1959;Cui, 1976Cui, , 1981He and Cai, 1984;Luo and Sun, 1994;Matsuoka and Setoguchi, 2000;Maisch et al, 2004;Watabe et al, 2007;Lopatin and Agadjanian, 2008;Hu et al, 2009;Matsuoka et al, 2016;Velazco et al, 2017), Europe (Charlesworth, 1855;Owen, 1857;Hennig, 1922;Waldman and Savage, 1972;Ensom, 1977Ensom, , 1994, and North America (Kermack, 1982;Sues, 1985Sues, , 1986Sues and Jenkins, 2006;Fedak et al, 2015), including Mexico (Clark and Hopson, 1985). All are considered herbivorous (K€ uhne, 1956;Sues, 1986), except Yuanotherium minor, which was described as having dental characteristics that suggest that it may have been omnivorous (Hu et al, 2009).…”

“…There is currently a lack of clarity on its diagnosis, systematics, anatomical features, and variability. This is becoming a pressing issue as new tritylodontid specimens continue to be discovered around the world (e.g., Matsuoka et al, 2016;Velazco et al, 2017) yet cannot easily be compared with Stereognathus. Lack of detailed descriptions of some genera has repercussions for phylogenetic analyses, including incorrect character scoring for Stereognathus.…”

Complementary approaches to tooth wear analysis in Tritylodontidae (Synapsida, Mammaliamorpha) reveal a generalist diet

“…To date, tritylodontids are known from Europe, Africa, Asia, North America, and Antarctica [9] but have never been reported from Australia, and likely have yet to be discovered in South America ([10] contra [11]). Body size in Tritylodontidae ranges from small, vole- to rat-sized taxa (the smallest are Lufengia delicata and then Yunnanodon brevirostris ) to large, wolf- or capybara-sized taxa ( Kayentatherium wellesi and Bienotherium magnum ) [10, 12]. Given the considerable range of body sizes in Tritylodontidae, we expect the food choice of at least the small- and large-bodied taxa to be different with respect to dietary composition and biomechanical properties of the ingested food items.…”