Reappraisal of supposed ‘dinocephalian’ specimens expands burnetiamorph diversity in the Guadalupian Tapinocephalus Assemblage Zone of South Africa
Date
2023-07
Authors
Day, Michael O.
Kammerer, Christian E.
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Abstract
Burnetiids are a rare, yet seemingly species-rich family of therapsids in the rocks of the Karoo Basin of South Africa. Discoveries over
the past 20 years have provided a greater understanding of the morphological variation within the group and have led to differing
hypotheses of burnetiid phylogeny and that of their parent clade, Burnetiamorpha. One posits the existence within Burnetiidae of two
subclades, Burnetiinae and Proburnetiinae, but this hypothesis invokes lengthy and thus problematic ghost lineages, particularly for
proburnetiines. Herewereview and describe cranial material from the Capitanian Tapinocephalus Assemblage Zone that was previously
referred to the dinocephalian therapsid Styracocephalus platyrhynchus, showing that it instead represents two new morphotypes of
proburnetiine burnetiids. One of these, Nierkoppia brucei gen. et sp. nov., is diagnosed by the autapomorphic presence of a supraorbital
boss ‘folded over’ the dorsal margin of the orbit, giving this structure a roughly ‘ear’ or ‘kidney’-shaped appearance; flattened,
posteriorly directed squamosal horns; a median frontal boss taller than the supraorbital bosses, reaching itsmaximumheight anterior to
them; and massive, rounded nuchal bosses borne on the postparietal and supraoccipital. The other specimen is left in open nomenclature
due to incompleteness, but represents a heavily pachyostosed proburnetiine similar to Lende and Leucocephalus. The recovery of
proburnetiines within theTapinocephalus Assemblage Zone shortens the ghost lineage of this clade and indicates that a diverse burnetiid
fauna was present in the Guadalupian Karoo, comparable to that now known from Tanzania and Zambia.