New whaitsioids (Therapsida: Therocephalia) from the Teekloof Formation of South Africa and therocephalian diversity during the end-Guadalupian extinction.

Adam K Huttenlocker,Roger M.H Smith

doi:10.7717/peerj.3868

Adam K Huttenlocker, Roger M.H Smith

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https://doi.org/10.7717/peerj.3868

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Abstract

Two new species of therocephalian therapsids are described from the upper Permian Teekloof Formation of the Karoo Basin, South Africa. They include two specimens of a whaitsiid, Microwhaitsia mendrezi gen. et sp. nov., and a single, small whaitsioid Ophidostoma tatarinovi gen. et sp. nov., which preserves a combination of primitive and apomorphic features. A phylogenetic analysis of 56 therapsid taxa and 136 craniodental and postcranial characters places the new taxa within the monophyletic sister group of baurioids—Whaitsioidea—with Microwhaitsia as a basal whaitsiid and Ophidostoma as an aberrant whaitsioid just outside the hofmeyriid+whaitsiid subclade. The new records support that whaitsioids were diverse during the early-late Permian (Wuchiapingian) and that the dichotomy between whaitsiid-line and baurioid-line eutherocephalians was established early on. The oldest Gondwanan whaitsiid Microwhaitsia and additional records from the lower strata of the Teekloof Formation suggest that whaitsioids had diversified by the early Wuchiapingian and no later than Pristerognathus Assemblage Zone times. Prior extinction estimates based on species counts are reflected in an analysis of origination/extinction rates, which imply increasing faunal turnover from Guadalupian to Lopingian (late Permian) times. The new records support a growing body of evidence that some key Lopingian synapsid clades originated near or prior to the Guadalupian-Lopingian boundary ca. 260–259 million years ago, but only radiated following the end-Guadalupian extinction of dinocephalians and basal therocephalian predators (long-fuse model). Ongoing collecting in older portions of the Teekloof Formation (e.g., Pristerognathus Assemblage Zone) will shed further light on early eutherocephalians during this murky but critical time in their evolutionary diversification.

Highlights

Therocephalians were a major clade of non-mammalian therapsids whose fossils are best represented in rocks of the middle to late Permian, How to cite this article Huttenlocker and Smith (2017), New whaitsioids (Therapsida: Therocephalia) from the Teekloof Formation of South Africa and therocephalian diversity during the end-Guadalupian extinction
The electronic version of this article in Portable Document Format (PDF) will represent a published work according to the International Commission on Zoological Nomenclature (ICZN), and the new names contained in the electronic version are effectively published under that Code from the electronic edition alone
We suggest that the apparent turnover of therocephalians can be characterized by a longfuse model in which classic late Permian clades originated concurrently with basal therocephalians of the middle Permian, but at lower abundances

Summary

Introduction

Therocephalians were a major clade of non-mammalian therapsids whose fossils are best represented in rocks of the middle to late Permian (ca. 272–251.9 million years ago), How to cite this article Huttenlocker and Smith (2017), New whaitsioids (Therapsida: Therocephalia) from the Teekloof Formation of South Africa and therocephalian diversity during the end-Guadalupian extinction. They attained remarkable ecological diversity with wide-ranging body sizes and myriad dental (and, dietary) specializations and other modifications of their feeding apparatus (Kemp, 1972a; Kemp, 1972b; Huttenlocker, 2014; Huttenlocker & Abdala, 2015; Huttenlocker, Sidor & Angielczyk, 2015). The later eutherocephalians that derived from this stock became highly diverse with up to 70 genera (Abdala, Rubidge & Van den Heever, 2008; Huttenlocker, 2013), and abruptly replaced the earlier, archaic groups in the Karoo Basin by Tropidostoma AZ times These eutherocephalians, along with the gorgonopsians, remained among the most abundant terrestrial predators in early–late Permian terrestrial assemblages in southern Africa (Smith & Botha-Brink, 2011; Smith, Rubidge & Van der Walt, 2012). A major dichotomy between baurioid-line and whaitsiid-line eutherocephalians may have already taken place prior to the early–late Permian Tropidostoma AZ, as some museum records of baurioid-line ‘ictidosuchids’ and whaitsiid-line hofmeyriids were collected from Pristerognathus AZ-equivalent rocks of the lower Teekloof Formation (reviewed in Huttenlocker, 2013 and this study)

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