Abstract
A new therocephalian taxon (Gorynychus masyutinae gen. et sp. nov.) is described based on a nearly complete skull and partial postcranium from the Permian Kotelnich locality of Russia. Gorynychus displays an unusual mixture of primitive (“pristerosaurian”) and derived (eutherocephalian) characters. Primitive features of Gorynychus include extensive dentition on the palatal boss and transverse process of the pterygoid, paired vomers, and a prominent dentary angle; derived features include the absence of the postfrontal. Gorynychus can be distinguished from all other therocephalians by its autapomorphic dental morphology, with roughly denticulated incisors and postcanines. Phylogenetic analysis recovers Gorynychus as a non-lycosuchid, non-scylacosaurid therocephalian situated as sister-taxon to Eutherocephalia. The identification of Gorynychus as the largest predator from Kotelnich indicates that therocephalians acted as apex predators in middle–late Permian transition ecosystems in Russia, corroborating a pattern observed in South African faunas. However, other aspects of the Kotelnich fauna, and Permian Russian tetrapod faunas in general, differ markedly from those of South Africa and suggest that Karoo faunas are not necessarily representative of global patterns.
Highlights
Therocephalians had perhaps the most unusual evolutionary trajectory of the major clades of non-mammalian therapsids
The earliest known therocephalians (Lycosuchidae and Scylacosauridae, historically united in the paraphyletic group “Pristerosauria” (Boonstra, 1953)), which are best represented in middle Permian sediments of the Karoo Basin of South Africa, were large-bodied predators (Boonstra, 1969; van den Heever, 1980, 1994)
Following the extinction of dinocephalians at the end of the Capitanian, therocephalians briefly served as the apex predators of the Karoo during the middle–late Permian transition represented by the
Summary
Therocephalians had perhaps the most unusual evolutionary trajectory of the major clades of non-mammalian therapsids. In Lycosuchus and other early therocephalians, the facial portion of the jugal terminates well posterior to the anterior edge of the lacrimal, but still forms a tall plate on the snout and occupies almost the entire ventral margin of the orbit (van den Heever, 1994). In addition to being preserved in the holotype, an isolated jugal is present on the referred block (Fig. 10), identifiable by the characteristic subtemporal curvature and well-developed process contributing to the postorbital bar. It is a topologically complex element composed of a laminar anterior process that forms much of the lateral margin of the choana and a broad main portion with a prominent central ridge bounded by medial and lateral depressions This central ridge extends anterolaterally to posteromedially and is confluent posteriorly with a ridge on the pterygoid, terminating with the palatal boss. Skeletons are known for a wide array of taxa, anatomical descriptions are currently available for only a select few (Kemp, 1986; Fourie & Rubidge, 2009; Botha-Brink & Modesto, 2011; Fourie, 2013)
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