Data from: Taxonomy of the proterosuchid archosauriforms (Diapsida: Archosauromorpha) from the earliest Triassic of South Africa, and implications for the early archosauriform radiation

Proterosuchidae is one of the first clades of Archosauriformes (archosaurs and closely related species) to appear in the fossil record, with the richest sample of the group coming from the Lystrosaurus Assemblage Zone (earliest Triassic) of South Africa. Four nominal proterosuchid species were described from South Africa during the twentieth century (Proterosuchus fergusi, Chasmatosaurus vanhoepeni, Chasmatosaurus alexanderi and Elaphrosuchus rubidgei), but interpretations of their taxonomy have been widely disparate. The most recent taxonomic revision concluded that P. fergusi is the only valid species and that the other nominal species are junior subjective synonyms of this taxon. This proposal was based on the interpretation that anatomical differences between the nominal species could be explained as a result of ontogenetic changes and/or post-mortem deformation. The recent discoveries of multiple new South African proterosuchid specimens provide an impetus to revisit their taxonomy. Based upon a comprehensive re-examination of all known specimens, as well as examination of other proterosuchid taxa in collections worldwide, we conclude that the holotype of Proterosuchus fergusi is undiagnostic. As a result, we propose a neotype (RC 846) for the species. ‘Chasmatosaurus vanhoepeni’ and ‘Elaphrosuchus rubidgei’ are considered subjective junior synonyms of P. fergusi. ‘Chasmatosaurus’ alexanderi is considered a valid species, for which we propose the new combination P. alexanderi comb. nov. A third species, P. goweri sp. nov., is erected on the basis of a single specimen (NMQR 880). All three species recognized here are taxonomically distinct from a previously described archosauriform maxilla from the lower Lystrosaurus AZ. As a result, we recognize a minimum of four archosauriform species following the Permo-Triassic mass extinction in South Africa. Our results suggest a greater species richness of earliest Triassic archosauriforms than previously appreciated, but that archosauriform morphological disparity remained low and did not expand until the late Early Triassic – early Mid-Triassic.原鳄科（Proterosuchidae）是化石记录中出现最早的主龙形类（Archosauriformes，即主龙类及其近缘类群）分支之一，该类群最丰富的标本采自南非的水龙兽组合带（Lystrosaurus Assemblage Zone，早三叠世最早期）。20世纪期间，南非曾记述过4个暂定的原鳄科物种：费氏原鳄（Proterosuchus fergusi）、范氏鞘鳄（Chasmatosaurus vanhoepeni）、亚历山大鞘鳄（Chasmatosaurus alexanderi）以及鲁氏懒鳄（Elaphrosuchus rubidgei），但学界对其分类学的解读长期存在极大分歧。最新的分类学修订研究认为，费氏原鳄是唯一有效物种，其余暂定物种均为该物种的次级主观同物异名。该结论的依据是，这些暂定物种间的解剖学差异可归因于个体发育变化和/或死后变形。近期南非多地发现的多件原鳄科新标本，为重新审视该类群的分类学提供了契机。通过对所有已知标本的全面重新检视，以及对全球馆藏的其他原鳄科类群标本的研究，我们发现费氏原鳄的正模标本（holotype）缺乏鉴定特征。据此，我们为该物种指定新模式标本（neotype，RC 846）。‘范氏鞘鳄’与‘鲁氏懒鳄’被认定为费氏原鳄的次级主观同物异名。‘亚历山大鞘鳄’则被视为有效物种，我们将其重新组合为亚历山大原鳄（P. alexanderi comb. nov.）。另有一新种P. goweri sp. nov.，基于单件标本（NMQR 880）建立。本文所认定的3个物种，均与此前记述的、产自下伏水龙兽组合带的一件主龙形类上颌骨分类学上截然不同。据此，我们确认南非二叠纪-三叠纪大灭绝（Permo-Triassic mass extinction）后存在至少4种主龙形类物种。本研究结果表明，早三叠世最早期的主龙形类物种丰富度高于此前认知，但该类群的形态分异度（morphological disparity）始终处于较低水平，直至早三叠世晚期—中三叠世早期才出现显著提升。