Tiarajudens eccentricusandAnomocephalus africanus, two bizarre anomodonts (Synapsida, Therapsida) with dental occlusion from the Permian of Gondwana

Abstract

Anomodontia was a highly successful tetrapod clade during the Permian and the Triassic. New morphological information regarding two bizarre basal anomodonts is provided and their palaeoecological significance is explored. The osteology of the recently discovered Tiarajudens eccentricus Cisneros et al. 2011, from the Brazilian Permian, is described in detail. The taxon exhibits unusual postcranial features, including the presence of gastralia. Additional preparation and computed tomography scans of the holotype of Anomocephalus africanus Modesto et al. 1999 discovered in the Karoo Basin of South Africa allow a reappraisal of this genus. Anomocephalus is similar to Tiarajudens with regard to several traits, including a battery of large, transversally expanded, palatal teeth. Molariform teeth are present in the mandible of the African taxon, providing additional insight into the function of the earliest tooth-occlusion mechanism known in therapsids. At least two waves of tooth replacement can be recognized in the palate of Anomocephalus. The outsized, blade-like caniniforms of the herbivorous Tiarajudens allow several non-exclusive ecological interpretations, among which we favour intraspecific display or combat. This behaviour was an alternative to the head-butting practised by the contemporary dinocephalians. Combat specializations that are considered typical of Cenozoic herbivores likely evolved during the Middle Permian, at the time the first communities with diverse, abundant tetrapod herbivores were being assembled.

The cranial morphology, phylogenetic position and biogeography of the upper Permian dicynodontCompsodon helmoedivan Hoepen (Therapsida, Anomodontia)

“…(), Cisneros et al . (, ) and Fröbisch & Reisz (). In terms of general skull morphology, Patranomodon is strikingly similar to the ‘dromasaurs’ (the grade of Karoo basal anomodonts consisting of Galechirus , Galeops and Galepus ) and its basal position in published phylogenies was based mainly on its extremely plesiomorphic jaw morphology and postcranium (Rubidge & Hopson ).…”

“…Cisneros et al . , ), making them the most basal anomodonts other than Biseridens . Patranomodon was recovered outside of Venyukovioidea + Chainosauria by Kammerer et al .…”

Evolution of facial innervation in anomodont therapsids (Synapsida): Insights from X‐ray computerized microtomography

“…The premaxilla is not preserved in the only specimen of Patranomodon , so it is impossible to assess whether rugosity associated with a ramphotheca was present. Such rugosity is absent in most other non‐dicynodont anomodonts ( Biseridens, Anomocephalus , Tiarajudens , venyukoviioids, Galechirus ), which display large premaxillary teeth instead of a beak (Brinkman, ; Ivakhnenko, ; Modesto & Rubidge, ; Liu et al, ; Cisneros, Abdala, Jashashvili, Bueno, & Dentzien‐Dias, ). Brinkman () suggested that an edentulous beak was present in Galeops and Galepus , which is important given that Galeops typically is reconstructed as the sister taxon of Dicynodontia in most phylogenetic analyses (e.g., Kammerer et al, ; Cox & Angielczyk, ; Angielczyk & Kammerer, ).…”

Tetrapod tracks in Permo–Triassic eolian beds of southern Brazil (Paraná Basin)

“…Regarding the dicynodonts, all the species that have preserved autopodia show both manus and pedes phalangeal formulae of 2-3-3-3-3 and metacarpals II and IV of very similar length ( Watson, 1913 , 1960 ; Cluver, 1978 ; King, 1985 , 1990 ; Rubidge, King & Hancox, 1994 ; Hopson, 1995 ), giving a symmetrical, near mesaxonic condition to their hands and feet, similar to the SLIA-1 and SLIA-2 tracks. Although this morphology is also common among non-dicynodont anomodonts ( Hopson, 1995 ; Cisneros et al, 2015 ), some of them have an elongated metacarpal IV (e.g., Galechirus ) or discoidal extra-phalanges in the third and fourth digits (e.g., Suminia ), making their autopodia more asymmetrical ( Fröbisch & Reisz, 2009 ).…”