A new burnetiid from the middle Permian of Zambia and a reanalysis of burnetiamorph relationships

Abstract

A new taxon of burnetiamorph therapsid, Mobaceras zambeziense gen. et sp. nov., is described on the basis of a partial skull recovered from the lower Madumabisa Mudstone Formation (Guadalupian) of Zambia. This taxon can be distinguished from all previously known burnetiamorphs by its unique cranial boss morphology, including a bulbous nasal boss on a 'stalk' and highly discretized, exaggerated anterior and posterior supraorbital bosses. Burnetiamorph phylogeny has recently become contentious; here, support for conflicting phylogenetic topologies is evaluated on a character-by-character basis and a revised phylogenetic analysis is presented. The clades Burnetiamorpha and Burnetiidae are supported with their traditional composition, including genera (viz. Bullacephalus and Pachydectes) recently assigned to a separate family (Bullacephalidae, here considered synonymous with Burnetiidae). The traditional dichotomy within Burnetiidae into Burnetiinae and Proburnetiinae is upheld, with Mobaceras recovered as a burnetiine, along with Bullacephalus, Burnetia, Niuksenitia, and Pachydectes.

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

“…Phylogenetic Position of Isengops Kammerer and Sidor (2021) recently published a comprehensive review of the characters used in most previous analyses of burnetiamorph phylogenetic relationships. Their paper was, in part, a response the results of Day et al (2016), who found unorthodox phylogenetic results markedly at contrast to the majority of those since the initial studies of the group (e.g., Sidor, 2000;Sidor and Welman, 2003;Sidor et al, 2004;Kammerer, 2016).…”

“…Surprisingly, they found currently recognized burnetiamorphs to be paraphyletic in some analyses, with the middle Permian Bullacephalus and Pachydectes forming a clade with Hipposaurus to the exclusion of other burnetiamorph taxa. Kammerer and Sidor (2021) reanalysis of the Day et al (2016) data set suggested that: (1) some characters could be excluded because they were either parsimony uninformative or strongly tied to ontogenetic status of the specimens under study, (2) some character state attributions were mistaken and were corrected in the revised data matrix, and (3) some characters had to be reformulated in order to better describe and encompass the range of variation seen within the ingroup. After their revisions, the Kammerer and Sidor (2021) resulting data set included 27 characters and 21 operational taxonomic units (all biarmosuchians).…”

“…To determine the phylogenetic position of Isengops, we added it to the complete data set of Kammerer and Sidor (2021). Thus, the current analysis includes 27 characters assessed in 22 taxa.…”

“…Geological research on the Madumabisa Mudstone Formation of the Luangwa Basin has concentrated on rocks exposed Data on other biarmosuchians can be found in Sidor (2015), Kammerer (2016), and Day et al (2016). Sidor et al (2015) mentioned the occurrence of burnetiamorphs in the Mid-Zambezi Basin of Zambia, but only one species has been named and described thus far (Kammerer and Sidor, 2021).…”

“…Sidor et al (2010) reported the first burnetiamorph material from the upper Permian of Tanzania, but did not name the single isolated skullcap. Likewise, Sidor et al (2014) mentioned the presence of burnetiamorph fossils from the lower Madumabisa Mudstone Formation in southern Zambia, which they considered Guadalupian in age based on the co-occurrence of tapinocephalid dinocephalians (see Day et al, 2015), with one species recently described as Mobaceras zambeziense by Kammerer and Sidor (2021). From the same beds, Whitney and Sidor (2016) described Wantulignathus gwembensis as a probable burnetiamorph, although the type material allowed referral only to Biarmosuchia indet.…”