Anomodontia Owen, 1860

Kammerer, Christian F. & Angielczyk, Kenneth D., 2009, A proposed higher taxonomy of anomodont therapsids, Zootaxa 2018, pp. 1-24 : 2-3

Anomodontia Owen, 1860 b

Definition: All taxa more closely related to Dicynodon lacerticeps Owen, 1845 , than Tapinocephalus atherstonei Owen, 1876 , Ictidorhinus martinsi Broom, 1913 b, Gorgonops torvus Owen, 1876 , or Scylacosaurus sclateri Broom, 1903 b.

Taxonomic comments: Anomodontia has had a convoluted taxonomic history, and usage of the term has gone through several major phases. As initially conceived by Owen (1860b), Anomodontia contained taxa currently considered to be dicynodonts (Owen’s “families” Dicynodontia, for Dicynodon and Ptychognathus , and Cryptodontia, for Oudenodon ) as well as non-synapsid reptiles (“family” Gnathodontia for the archosauromorph Rhynchosaurus ). Owen (1861) removed Gnathodontia from Anomodontia and included Cynodontia instead. In Owen’s (1876) monographic treatment of South African fossil reptiles, he removed cynodonts from Anomodontia , restricting it to dicynodonts (Dicynodontia, Cryptodontia, and Endothiodontia). In the late 19th and early 20th century, various workers (e. g., Seeley 1888; Watson 1917) expanded the composition of Anomodontia to include all non-mammalian synapsids. Broom (1905) argued that Anomodontia should be restricted to dicynodonts, but this usage did not regain wide acceptance until the 1920s and 1930s (e. g., Nopcsa 1923, 1928; Broom 1932). Watson & Romer’s (1956) highly influential classification of therapsids united dicynodonts, the Russian “venyukoviamorphs”, and herbivorous dinocephalians (tapinocephalians) within Anomodontia . Later, Romer (1966) also included the supposedly carnivorous dinocephalians ( Anteosauridae and Titanosuchidae , the latter of which are now believed to have been herbivores [e. g., Boonstra 1963; Kemp 1982; Hopson & Barghusen 1986]) within Anomodontia , and the use of Anomodontia to refer to Dinocephalia + Dicynodontia was dominant until the 1990s (e. g., King 1988). With the application of cladistic methodology to studying therapsid relationships, the monophyly of Dinocephalia + Dicynodontia was called into question ( Hopson & Barghusen 1986; Gauthier et al. 1988; Hopson 1991; Grine 1997; Sidor & Hopson 1998), and dinocephalians were removed from Anomodontia . Current usage of Anomodontia universally refers to the clade containing both dicynodonts and the basal taxa formerly called “dromasaurs” or “venyukoviamorphs” (e. g., Modesto et al. 1999, 2003a; Modesto & Rubidge 2000; Angielczyk & Kurkin 2003a; Angielczyk 2004; Fröbisch 2007; Fröbisch & Reisz 2008).

Modesto & Rubidge (2000, p. 516) proposed a node-based definition for Anomodontia containing “the last common ancestor of Anomocephalus africanus, Patranomodon nyaphulii , Galeops whaitsi , Eodicynodon oosthuizeni , and Dicynodon lacerticeps , and all its descendants.” We advocate a stem-based definition for this taxon instead, utilizing exemplars from all of the other major therapsid groups ( Dinocephalia, Biarmosuchia, Gorgonopsia , and Eutheriodontia) as external specifiers. Although relationships between the major therapsid taxa remain highly contentious (Rubidge & Sidor 2001; Kemp 2006), the groups themselves have remained remarkably stable, and current phylogenies ( Hopson & Barghusen 1986; Sidor 2000) support their reciprocal monophyly. Use of a stem-based definition for the major therapsid clade Anomodontia allows for greatest inclusivity in the likely event that a therapsid basal to Anomocephalus with anomodont characteristics is discovered. Battail (2000) suggested that the problematic Chinese taxon Biseridens , originally described as an “eotitanosuchian” ( Li & Cheng 1997), might represent just such a therapsid. Usage of a node-based definition for Anomodontia ultimately would have destabilizing results for therapsid taxonomy, necessitating either the creation of new clade names for each node outward from Anomocephalus to refer to all ‘anomodont-like’ therapsids, or redefinition of Anomodontia with reference to each new taxon.

Revised diagnosis: Only three phylogenetic analyses ( Modesto et al. 1999; Fröbisch 2007; Fröbisch & Reisz 2008) have included Anomocephalus africanus, the most basal anomodont recognized to date, and we use these papers as sources of autapomorphies for Anomodontia . The most consistently cited autapomorphies of Anomodontia are: (1) serrations absent on marginal teeth; (2) mandibular fenestra present; (3) zygomatic arch bowed dorsally. A complete list of autapomorphies from each paper for this and all subsequent clades discussed herein can be found in the Appendix.