An early geikiid dicynodont from theTropidostomaAssemblage Zone (late Permian) of South Africa.
Based on specimens previously identified asTropidostoma, a new taxon of dicynodont (Bulbasaurus phylloxyrongen. et sp. nov.) from the Karoo Basin of South Africa is described.Bulbasaurusis a medium-sized dicynodont (maximum dorsal skull length 16.0 cm) restricted to theTropidostomaAssemblage Zone (early Lopingian) of the Beaufort Group.Bulbasauruscan be distinguished fromTropidostomaby 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 ofBulbasaurusin a phylogenetic analysis of anomodont therapsids recovers it as a member of Geikiidae, a clade of otherwise later Permian dicynodonts such asAulacephalodonandPelanomodon.Bulbasaurusexhibits many of the characters typical of adultAulacephalodon, but at substantially smaller skull size (these characters are absent in comparably-sizedAulacephalodonjuveniles), suggesting that the evolution of typical geikiid morphology preceded gigantism in the clade.Bulbasaurusis the earliest known geikiid and the only member of the group known from theTropidostomaAssemblage 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.
Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany; Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa.
Christian F
CF
Kammerer
Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa; Iziko Museums of South Africa, Cape Town, South Africa.
Roger M H
RM
Smith
Dicynodontia; Ghost lineage; Karoo Basin; Permian; Phylogeny; South Africa; Synapsida; Therapsida