[Papers in Palaeontology, 2021, pp. 1–35] A NEW BURNETIID FROM THE MIDDLE PERMIAN OF ZAMBIA AND A REANALYSIS OF BURNETIAMORPH RELATIONSHIPS by CHRISTIAN F. KAMMERER1 and CHRISTIAN A. SIDOR2 1North Carolina Museum of Natural Sciences, 11 W. Jones Street, Raleigh, NC 27601, USA; [email protected] 2Department of Biology & Burke Museum, University of Washington, Seattle, WA 98195-1800, USA; [email protected] Typescript received 24 April 2020; accepted in revised form 17 August 2020 Abstract: A new taxon of burnetiamorph therapsid, analysis is presented. The clades Burnetiamorpha and Bur- Mobaceras zambeziense gen. et sp. nov., is described on the netiidae are supported with their traditional composition, basis of a partial skull recovered from the lower Madumabisa including genera (viz. Bullacephalus and Pachydectes) recently Mudstone Formation (Guadalupian) of Zambia. This taxon assigned to a separate family (Bullacephalidae, here consid- can be distinguished from all previously known burneti- ered synonymous with Burnetiidae). The traditional dichot- amorphs by its unique cranial boss morphology, including a omy within Burnetiidae into Burnetiinae and Proburnetiinae bulbous nasal boss on a ‘stalk’ and highly discretized, exag- is upheld, with Mobaceras recovered as a burnetiine, along gerated anterior and posterior supraorbital bosses. Burneti- with Bullacephalus, Burnetia, Niuksenitia, and Pachydectes. amorph phylogeny has recently become contentious; here, support for conflicting phylogenetic topologies is evaluated Key words: Synapsida, Therapsida, Burnetiamorpha, Per- on a character-by-character basis and a revised phylogenetic mian, Guadalupian, Zambia. C RANIAL ornamentation in the form of pachyostosed this clade would have been highly visible and distinctive ‘horns’, bosses, or crests evolved numerous times in Per- even if covered only by a thin layer of skin. mian and Triassic therapsids. Nasal bosses are present in Unfortunately, an understanding of the palaeobiological most dicynodonts, supraorbital bosses are present in both implications of burnetiamorph cranial ornaments has anteosaurian dinocephalians and rubidgeine gorgonop- been hindered by a paucity of fossils. Burnetiamorphs are sians, and median frontal bosses are present in tapinoce- notoriously rare components of the most intensely sam- phalid and some anteosaurian dinocephalians (Angielczyk pled Permian tetrapod-bearing beds, those of the South 2001; Rubidge & Sidor 2001; Kammerer 2011, 2016a). African Beaufort Group (Smith et al. 2012; Sidor 2015). Especially baroque cranial ornamentation is present in the Of the eight described species of South African burneti- Burnetiamorpha, a subclade of the basal therapsid group amorphs (Bullacephalus jacksoni, Burnetia mirabilis, Biarmosuchia. All known burnetiamorph skulls feature Lemurosaurus pricei, Leucocephalus wewersi, Lobalopex frontal and supraorbital ornamentation, and most also mordax, Lophorhinus willodenensis, Pachydectes elsi, and bear nasal, supratemporal, and zygomatic bosses (Rubidge Paraburnetia sneeubergensis), only Lemurosaurus pricei is & Sidor 2002; Smith et al. 2006; Kruger et al. 2015; Kam- known from multiple specimens (Sidor & Welman 2003). merer 2016b). Although functional explanations have Because of this rarity, it is difficult to assess whether bur- been proposed for the supraorbital bosses of some therap- netiamorph cranial ornaments exhibited intraspecific vari- sids (Ivakhnenko 2003; Kammerer 2011), the complexity ation (be it ontogenetic, sexual, or otherwise), which is and apparent species-specific morphologies of burneti- particularly problematic given the importance of these amorph cranial ornaments are more suggestive of a dis- ornaments both for species diagnoses and phylogenetic play purpose (Sidor et al. 2017). Although Kulik & analysis (Sidor et al. 2017). The only evidence for ontoge- Sidor’s (2019) histological examination of two burneti- netic variation in burnetiamorphs comes from Lemuro- amorph skull caps failed to show definitive evidence for saurus pricei, in which the holotype (BP/1/816, snout overlying soft-tissue structures (based on the criteria pro- length 41.2 mm) is substantially smaller than the referred posed by Hieronymus et al. 2009), cranial ornaments in specimen (NMQR 1702, snout length 73.3 mm). © 2021 The Authors. Papers in Palaeontology © 2021 The Palaeontological Association. This article has been contributed to by US Government employees and their work is in the public domain in the USA. doi: 10.1002/spp2.1341 1 2 PAPERS IN PALAEONTOLOGY Outside of South Africa, burnetiamorph records have SYSTEMATIC PALAEONTOLOGY historically also been rare, with only three named taxa, each represented by a single specimen (the holotypes of THERAPSIDA Broom, 1905 Niuksenitia sukhonensis and Proburnetia viatkensis from BURNETIAMORPHA Broom, 1923 Russia and Lende chiweta from Malawi; Ivakhnenko et al. BURNETIIDAE Broom, 1923 1997; Rubidge & Sidor 2002; Kruger et al. 2015). Recent BURNETIINAE Broom, 1923 fieldwork in Tanzania and Zambia (Sidor et al. 2015) has challenged the notion that burnetiamorphs were always Genus MOBACERAS nov. uncommon components of their faunas, however. Sidor et al. (2010) reported a burnetiamorph skull cap from the LSID. urn:lsid:zoobank.org:act:EB58B3E8-9FFA-4E87-86FD- basal conglomerate horizon of the Usili Formation in 37EB4B9F001F Tanzania, and an additional six skull caps from this hori- zon have since been recovered (CAS, pers. obs.) In the Type species. Mobaceras zambeziense sp. nov. lower Madumabisa Mudstone Formation of Zambia, 14 burnetiamorph skull caps have been recovered from 13 Derivation of name. Genus name Mobaceras from moba, the localities, a number surpassed only by isolated tapinoce- name of the knob-thorn acacia tree in the Tonga language (Chi- jέqᾰς phalid teeth as the most commonly encountered verte- tonga) of southern Zambia, and the Ancient Greek (ceras) brate fossils in this unit (Sidor et al. 2014). Kulik & Sidor meaning horn, in reference to the knob-like cranial bosses of (2019) described the osteohistology and external anatomy this taxon. of three of these Zambian skull caps, but left them Diagnosis. As for the type and only species. unnamed because of their incompleteness. Here, we describe the first burnetiamorph specimen from this assemblage preserving more than just the skull roof, rec- Mobaceras zambeziense sp. nov. ognize it as a novel taxon, and discuss its implications for Figures 1–4 burnetiamorph phylogeny. Institutional abbreviations. AMNH FARB, American Museum of LSID. urn:lsid:zoobank.org:act:9BD331C6-39EE-4F35-BC7A- Natural History, Fossil Amphibian, Reptile, and Bird Collection, 894935BA734D New York, USA; BP, Evolutionary Studies Institute (formerly the Bernard Price Institute for Palaeontological Research), University of the Witwatersrand, Johannesburg, South Africa; Derivation of name. Species name zambeziense in reference to CGP/CGS, Council for Geoscience, Pretoria, South Africa; MAL, the Zambezi River valley, where both specimens of this taxon Malawi Department of Antiquities Collection, Lilongwe and were collected. Nguludi, Malawi; NHCC, National Heritage Conservation Com- mission, Lusaka, Zambia; NHMUK, Natural History Museum, Holotype. NHCC LB133, a partial skull missing the anterior por- London, UK; NMQR, National Museum, Bloemfontein, South tion of the snout and the mandible. Africa; NMT, National Museum of Tanzania, Dar es Salaam, Tanzania; PIN, Paleontological Institute of the Russian Academy Referred material. NHCC LB593, a skull cap preserving much of of Sciences, Moscow, Russia; RC, Rubidge Collection, Wellwood, the interorbital and intertemporal regions. Graaff-Reinet, South Africa; SAM, Iziko: South African Museum, Cape Town, South Africa; TM, Ditsong, National Museum of Locality and horizon. Collected from locality L157 (type) and Natural History (formerly the Transvaal Museum), Pretoria, L174 (referred specimen), which are part of a cluster of closely South Africa. spaced sites within a band of outcrop c. 18 km southwest of the village of Chamwe, Gwembe District (Southern Province, Zam- bia). Although not continuous with the outcrop discussed by MATERIAL AND METHOD Sidor et al. (2014) or Whitney & Sidor (2016), the inferred stratigraphic position is the same: these rocks are probably part Comparisons with other biarmosuchians were based on of the informally recognized ‘middle calcareous member’ of the Madumabisa Mudstone Formation (Gair 1959; Nyambe & first-hand examination of all published specimens by CFK Dixon 2000). Based on the presence of tapinocephalid dinoce- and CAS. Fossil preparation of NHCC LB133 was accom- phalian fossils, we consider these rocks to be Guadalupian in age plished at the University of Washington Burke Museum (Olroyd & Sidor 2017). by Bruce Crowley; matrix surrounding the fossil was removed mechanically with airscribes and pin vices, fol- Diagnosis. A burnetiid burnetiamorph distinguished from all lowed by two acid baths (submersion in sulphamic acid taxa other than Bullacephalus and Burnetia by the presence of for a total of c. 4 hours, followed by overnight rinsing). two pairs of large supraorbital bosses (one pair above the dorsal KAMMERER & SIDOR: ZAMBIAN BURNETIID 3 FIG. 1. The holotype of Mobaceras zambeziense, gen. et sp. nov. (NHCC LB133). Photographs and interpretative drawings of the skull in: A, dorsal; B, ventral view. Abbreviations: asb, anterior supraorbital boss; bt, basal tuber; cc, foramen for carotid canal; ec, ectopterygoid;