A new therocephalian (Gorynychus masyutinae gen. et sp. nov.) from the Permian Kotelnich locality, Kirov Region, Russia

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.

Morphological evolution in therocephalians breaks the hypercarnivore ratchet

“…Despite the addition of new data (including a comparatively small outgroup cynodont) and allowing rate variation, the ancestral size of therocephalians is still found to be large, within the ranges observed by the macropredatory scylacosaurids. In fact, the new data and methods showed the ancestral therocephalian skull length to be slightly larger than previously found [28]: 193 mm, roughly that of wolf-sized therocephalian Gorynychus [21].…”

“…The phylogenetic framework for this study is a recent and comprehensive phylogenetic analysis of therocephalians [21]. The character-taxon matrix from this study was expanded by the addition of a non-therocephalian outgroup: the recently described cynodont Abdalodon [29].…”

“…Therocephalia is a therapsid lineage that first appears in the fossil record in the middle Permian sediments of the Karoo Supergroup of South Africa [18]. The lineage includes a diverse range of morphologies, including large predators, small generalist carnivores and insectivores, and small herbivores [19][20][21]. In recent publications [21,22], it was commented that, unlike other therapsid lineages, therocephalians appear to show multiple distinct waves of niche occupation.…”

“…The lineage includes a diverse range of morphologies, including large predators, small generalist carnivores and insectivores, and small herbivores [19][20][21]. In recent publications [21,22], it was commented that, unlike other therapsid lineages, therocephalians appear to show multiple distinct waves of niche occupation. The earliest therocephalians known are scylacosaurids [18], an assemblage of questionable monophyly [21][22][23][24] containing large-bodied predatory species, which represented the top predators across the middle-late Permian transition [21,25,26].…”

“…In recent publications [21,22], it was commented that, unlike other therapsid lineages, therocephalians appear to show multiple distinct waves of niche occupation. The earliest therocephalians known are scylacosaurids [18], an assemblage of questionable monophyly [21][22][23][24] containing large-bodied predatory species, which represented the top predators across the middle-late Permian transition [21,25,26]. Towards the latter stages of the Permian, however, these were replaced by the predominantly small-bodied insectivorous Eutherocephalia, and later in the Triassic by herbivorous Bauriidae.…”