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

PeerJ

article

Christian F. Kammerer¹  Roger M.H. Smith² 

[1] Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung;Evolutionary Studies Institute, University of the Witwatersrand;Iziko Museums of South Africa

关键词: Synapsida;    Therapsida;    Dicynodontia;    Permian;    Karoo Basin;    South Africa;    Ghost lineage;    Phylogeny;   

DOI  :  10.7717/peerj.2913

学科分类：社会科学、人文和艺术（综合）

来源: Inra

【 摘 要 】

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.

【 授权许可】

CC BY