Data_Sheet_1_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.DOCX

A new burnetiamorph therapsid, Isengops luangwensis, 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. Isengops 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 Cistecephalus Assemblage Zone of South Africa, suggesting a Wuchiapingian age. Isengops 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: Lemurosaurus is basal, Lobalopex and Isengops are proximate burnetiid outgroups, and Bullacephalus, Burnetia, Mobaceras, Niuksenitia, and Pachydectes 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.

本研究基于赞比亚东北部卢安瓜盆地（Luangwa Basin）马杜马巴泥岩组（Madumabisa Mudstone Formation）上部产出的部分头骨标本，记述了1个全新的伯内特兽类（burnetiamorph）兽孔目（therapsid）新属新种——伊森贡兽（Isengops luangwensis），gen. et sp. nov.。伊森贡兽的鉴别特征包括：简化的腭齿、脊状腭骨-翼状突（palatine-pterygoid）隆起、轭骨（jugal）的腭面暴露区域向前延伸甚远、高突的三角锥状眶上隆起（supraorbital boss），以及侧颞颥孔（lateral temporal fenestra）背缘处的凹坑。马杜马巴泥岩组上部沉积于裂谷盆地环境，其岩相特征表现为无槽流发育、存在陆上干燥作用与沉积间断阶段，且有成土作用发生；该地层可通过生物地层学手段与南非的二齿兽组合带（Cistecephalus Assemblage Zone）上部对比，其地质时代被限定为吴家坪阶（Wuchiapingian）。伊森贡兽是赞比亚境内发现的第二类伯内特兽类，其所在的四足动物组合与泛大陆南部吴家坪阶时期的其他四足动物组合具有极高的相似性。本次针对巴莫兽亚目（Biarmosuchia）的分支系统学（cladistic）分析共得到500余棵最简约树（most parsimonious trees），其结果总体上印证了此前针对伯内特兽类的研究结论：Lemurosaurus为基部类群，Lobalopex与伊森贡兽为伯恩蒂兽科（burnetiid）的近缘外类群，而Bullacephalus、Burnetia、Mobaceras、Niuksenitia与Pachydectes均隶属于伯恩蒂兽亚科（burnetiines）。此外，俄罗斯产出的巴莫兽类在分支系统树中呈分散分布，并未形成彼此对应的姊妹群（sister taxon）关系。伯内特兽类展现出丰富多样的颅部装饰（cranial adornments）特征，且物种丰富度较高（共计13个物种）；相较于目前已发现的约16件标本而言，这一物种丰富度尤为突出。正如其他一些四足动物类群（如角龙类恐龙）的相关研究结论所示，伯内特兽类的化石记录支持颅部装饰与物种形成速率提升之间存在宏观进化关联的推论。