The emblematic South African therocephalian Euchambersia in China: a new link in the dispersal of late Permian vertebrates across Pangea

Abstract

Therapsids were widely distributed in Pangea in the late Permian. South Africa in Gondwana and Russia in Laurasia are the principal areas recording tetrapods (including therapsids) of this age. More recent field explorations have increased the importance of Chinese late Permian fossil assemblages. This is clearly reflected in the discovery of several new therocephalians from the Naobaogou Formation in Nei Mongol. Here, we report a therocephalian from that unit identified as a new species of the emblematic South African taxon Euchambersia . The new species, Euchambersia liuyudongi , is represented by a well-preserved skull and mandible showing a well-developed maxillary fossa and the absence of postcanine teeth. This is the third akidnognathid therocephalian recovered from the Naobaougou Formation, but oddly, the two basal Chinese akidnognathids previously known were recovered from a younger unit of the formation than the derived E. liuyudongi . This is the first time that the same therocephalian genus has been recorded in northern and southern continents, making the record of the Naobaougou Formation key to understanding the evolution of late Permian continental fauna in general, and of akidnognathid therocephalians in particular.

The origin and evolution of Cynodontia (Synapsida, Therapsida): Reassessment of the phylogeny and systematics of the earliest members of this clade using 3D‐imaging technologies

“…Like most other major therapsid clades, Therocephalia, a species‐rich and ecomorphologically varied group, first diversified during the middle Permian and showed its highest diversity in the late Permian (e.g., Abdala et al, 2008; Day & Rubidge, 2020; Day & Smith, 2020; Huttenlocker & Smith, 2017; Kammerer, 2023; Pusch et al, 2020; Rubidge & Day, 2020; Smith, 2020; Viglietti, 2020). This lineage has generally been considered as monophyletic by recent authors (Hopson & Barghusen, 1986; Huttenlocker, 2009; Huttenlocker & Sidor, 2016, 2020; Huttenlocker & Smith, 2017; Liu & Abdala, 2019, 2020, 2022; Pusch et al, 2021, 2023; Sidor et al, 2022; van den Heever, 1994). By contrast, Abdala (2007) and Botha et al (2007) recovered Therocephalia as paraphyletic, with the whaitsiid Theriognathus as the sister‐taxon of cynodonts in their phylogenetic analyses, a hypothesis previously suggested by Kemp (1972).…”

“…The absence of cynodonts in middle Permian strata has led some researchers to propose that cynodonts are in fact derived from within Therocephalia, with their closest relatives being members of the family Whaitsiidae, rendering Therocephalia paraphyletic (Abdala, 2007; Abdala et al, 2008; Botha et al, 2007; Kemp, 1972). However, more recent phylogenetic analyses of therocephalians and early cynodonts (e.g., Huttenlocker, 2009; Huttenlocker & Sidor, 2016, 2020; Huttenlocker & Smith, 2017; Liu & Abdala, 2019, 2020, 2022; Pusch et al, 2021, 2023; Sidor et al, 2022) support reciprocal monophyly of Cynodontia and Therocephalia, implying a ghost lineage of as much as 10 million years between the earliest therocephalian records and the first appearance of Cynodontia (Angielczyk & Kammerer, 2018). Despite the generally consistent recent recovery of this topology, it must be noted that this relationship is poorly supported, typically requiring only a few additional steps to pull cynodonts into Therocephalia.…”

The tetrapod fauna of the upper Permian Naobaogou Formation of China: 10. Jimusaria monanensis sp. nov. (Dicynodontia) shows a unique epipterygoid

“…A contact between the epipterygoid and the prootic is a relatively “derived” feature in therapsids. Some therocephalians possess a dumb-bell-shaped epipterygoid, and that dorsal expanding portion of the ascending ramus of the epipterygoid contacts the prootic ( Barry, 1965 ; Durand, 1991 ; Huttenlocker, Sidor & Smith, 2011 ; Liu & Abdala, 2022 ). Some therocephalians and some cynodonts have a plate-like epipterygoid which sutures with the prootic posteriorly and forms part of the lateral wall of the braincase ( Barry, 1965 ; Kemp, 1972 ; Olson, 1944 ).…”

Weighing in on miniaturization: New body mass estimates for Triassic eucynodonts and analyses of body size evolution during the cynodont‐mammal transition

“…Here, we apply the framework proposed by Filippini et al (2022) to estimate body masses of 27 cynodont (including the small to medium‐sized probainognathian and cynognathian representatives), and two Therocephalia ( Regisaurus and Theriodesmus ; sister clade to Cynodontia, Liu & Abdala, 2022) species, providing what is, to our knowledge, the biggest collection of body mass estimates for Triassic cynodonts to date. Then we investigate macroevolutionary patterns regarding body size in Triassic cynodonts using phylogenetic comparative methods to estimate body size disparity through time and to detect possible shifts in evolutionary rates, testing Rowe (1993)'s miniaturization hypothesis for the origin of mammals.…”