An early geikiid dicynodont from the Tropidostoma Assemblage Zone (late Permian) of South Africa.

Christian F Kammerer,Roger M.H Smith

doi:10.7717/peerj.2913

Christian F Kammerer, Roger M.H Smith

Open Access

https://doi.org/10.7717/peerj.2913

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Journal: PeerJ	Publication Date: Jan 31, 2017
Citations: 16	License type: CC BY 4.0

Affiliation: University of the Witwatersrand, Museum für Naturkunde

Abstract

Based on specimens previously identified as Tropidostoma, a new taxon of dicynodont (Bulbasaurus phylloxyron gen. et sp. nov.) from the Karoo Basin of South Africa is described. Bulbasaurus is a medium-sized dicynodont (maximum dorsal skull length 16.0 cm) restricted to the Tropidostoma Assemblage Zone (early Lopingian) of the Beaufort Group. Bulbasaurus can be distinguished from Tropidostoma by an array of characters including the presence of a tall, sharp premaxillary ridge, large, rugose, nearly-confluent nasal bosses, a nasofrontal ridge, massive tusks, robust pterygoids, prominently twisted subtemporal bar, and absence of a distinct postfrontal. Inclusion of Bulbasaurus in a phylogenetic analysis of anomodont therapsids recovers it as a member of Geikiidae, a clade of otherwise later Permian dicynodonts such as Aulacephalodon and Pelanomodon. Bulbasaurus exhibits many of the characters typical of adult Aulacephalodon, but at substantially smaller skull size (these characters are absent in comparably-sized Aulacephalodon juveniles), suggesting that the evolution of typical geikiid morphology preceded gigantism in the clade. Bulbasaurus is the earliest known geikiid and the only member of the group known from the Tropidostoma Assemblage Zone; discovery of this taxon shortens a perplexing ghost lineage and indicates that abundant clades from the later Permian of South Africa (e.g., Geikiidae, Dicynodontoidea) may have originated as rare components of earlier Karoo assemblage zones.

Highlights

Several major turnovers in tetrapod faunal composition occurred in the Karoo Basin of South Africa during the span of time recorded in the Permo-Triassic Beaufort Group (Rubidge, 1995)
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
Bulbasaurus phylloxyron is identified as a new taxon of dicynodont, representing the earliest known record for the family Geikiidae and eliminating the ghost lineage for this clade in the Tropidostoma Assemblage Zone (AZ)

Summary

Introduction

Several major turnovers in tetrapod faunal composition occurred in the Karoo Basin of South Africa during the span of time recorded in the Permo-Triassic Beaufort Group (Rubidge, 1995). The primary victims of mid-Permian extinction among Karoo tetrapods were the dinocephalian therapsids, a group that, ecologically diverse and species-rich (Boonstra, 1969; Kammerer, 2011), represent a relatively small component of middle Permian faunas in terms of specimen abundance (Smith, Rubidge & van der Walt, 2012). Among dicynodont taxa whose ranges do not extend into the late Permian, most are components of the earliest Karoo faunal assemblages, none of whose members even make it to the end of the middle Permian (e.g., Eodicynodon, Lanthanostegus, Colobodectes) (Modesto, Rubidge & Welman, 2002; Angielczyk & Rubidge, 2009). The few dicynodont taxa that are apparent victims of the mid-Permian extinction (Brachyprosopus broomi and Robertia broomiana) have close relatives (at the ‘family level’) that thrive in the late Permian (Angielczyk & Rubidge, 2013; Cox & Angielczyk, 2014; Angielczyk et al, 2016)

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