AUTHOR=Sidor Christian A. , Tabor Neil J. , Smith Roger M. H. 

TITLE=A New Late Permian Burnetiamorph From Zambia Confirms Exceptional Levels of Endemism in Burnetiamorpha (Therapsida: Biarmosuchia) and an Updated Paleoenvironmental Interpretation of the Upper Madumabisa Mudstone Formation

JOURNAL=Frontiers in Ecology and Evolution

VOLUME=9

YEAR=2021

URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2021.685244

DOI=10.3389/fevo.2021.685244

ISSN=2296-701X

ABSTRACT=<p>A new burnetiamorph therapsid, <italic>Isengops luangwensis</italic>, gen. et sp. nov., is described on the basis of a partial skull from the upper Madumabisa Mudstone Formation of the Luangwa Basin of northeastern Zambia. <italic>Isengops</italic> is diagnosed by reduced palatal dentition, a ridge-like palatine-pterygoid boss, a palatal exposure of the jugal that extends far anteriorly, a tall trigonal pyramid-shaped supraorbital boss, and a recess along the dorsal margin of the lateral temporal fenestra. The upper Madumabisa Mudstone Formation was deposited in a rift basin with lithofacies characterized by unchannelized flow, periods of subaerial desiccation and non-deposition, and pedogenesis, and can be biostratigraphically tied to the upper <italic>Cistecephalus</italic> Assemblage Zone of South Africa, suggesting a Wuchiapingian age. <italic>Isengops</italic> is the second burnetiamorph recognized from Zambia and is part of a tetrapod assemblage remarkably similar to others across southern Pangea during the Wuchiapingian. A revised cladistic analysis of Biarmosuchia yielded over 500 most parsimonious trees that generally reaffirm the results of previous analyses for burnetiamorphs: <italic>Lemurosaurus</italic> is basal, <italic>Lobalopex</italic> and <italic>Isengops</italic> are proximate burnetiid outgroups, and <italic>Bullacephalus, Burnetia</italic>, <italic>Mobaceras</italic>, <italic>Niuksenitia</italic>, and <italic>Pachydectes</italic> are burnetiines. Furthermore, Russian biarmosuchians are scattered throughout the tree and do not form sister taxon relationships with each other. Burnetiamorphs display a wide disparity of cranial adornments and are relatively speciose (13 species), especially when compared to the number of specimens discovered to date (∼16 specimens). As has been suggested in some other tetrapod clades (e.g., ceratopsian dinosaurs), the burnetiamorph fossil record supports an inferred macroevolutionary relationship between cranial adornment and increased speciation rate.</p>