The first geikiid dicynodont, <i>Aulacephalodon kapoliwacela</i>, sp. nov. (Therapsida, Anomodontia), from the upper Madumabisa Mudstone Formation, Zambia

The upper Madumabisa Mudstone Formation is a richly fossiliferous rock formation exposed in the Luangwa Basin in Zambia, with well-documented upper Permian vertebrate assemblages comparable to those of coeval basins in Tanzania and South Africa. The tetrapod communities of the upper Madumabisa Mudstone include 20 species of dicynodonts. Although most Permian dicynodont clades are represented in the upper Madumabisa Mudstone assemblages, the ornamented clade Geikiidae, which occurs in both the Karoo and Ruhuhu basins, has yet to be reliably reported in the Luangwa Basin; historical reports likely represent other cryptodont taxa. We report a new species of geikiid, <i>Aulacephalodon kapoliwacela</i>, sp. nov., known from both the lower and upper assemblages of the upper Madumabisa Mudstone Formation. This species closely resembles the abundant South African taxon <i>Aulacephalodon bainii</i>, including bearing robust tusks, bosses on the squamosals, and a tall ascending process of the jugal, but differs in the absence of a pineal boss and differing ontogenetic trajectories of the postfrontal and postcaniniform crests. We also provisionally rediagnose <i>A. bainii</i> using only characters visible in the holotype, and for the first time provide a diagnosis for the genus. Phylogenetic analysis supports a close relationship between Zambian and South African geikiids. Multiple juvenile individuals of <i>A. kapoliwacela</i> help clarify ontogenetic trends within Geikiidae, including differences in development and fusion of the postfrontal between geikiid species. Large wear facets on the tusks of some individuals indicate substrate-focused foraging behavior in <i>Aulacephalodon</i>.赞比亚卢安瓜盆地出露的上马杜马比萨泥岩组（upper Madumabisa Mudstone Formation）是一处富含化石的岩石地层，其产出的晚二叠世脊椎动物组合已有详实研究记录，可与坦桑尼亚、南非同期盆地的同类组合相媲美。上马杜马比萨泥岩组的四足动物群落包含20种二齿兽类（dicynodonts）。尽管该组合涵盖了多数二叠纪二齿兽类演化支，但见于卡鲁盆地（Karoo Basin）与鲁胡胡盆地（Ruhuhu Basin）的具纹饰演化支盖基兽科（Geikiidae），在卢安瓜盆地尚未有可靠报道；此前的历史记录所指向的类群大概率应为其他隐齿兽类群。本文报道盖基兽科一新种：<i>Aulacephalodon kapoliwacela</i> sp. nov.（新种），其化石发现于上马杜马比萨泥岩组的下部与上部组合层位。该种与南非广布的贝恩大头颅兽（<i>Aulacephalodon bainii</i>）形态高度相似，均具有粗壮的獠牙、鳞状骨上的隆突以及高耸的轭骨升突，但二者存在显著差异：新种无松果隆突，且额后骨与犬齿后嵴的个体发育轨迹有所不同。本文同时仅依据正模标本可观测的特征，对贝恩大头颅兽（<i>A. bainii</i>）进行了临时性重新修订，并首次为大头颅兽属（<i>Aulacephalodon</i>）提供了属级鉴定特征。系统发育分析结果显示，赞比亚与南非的盖基兽类类群亲缘关系密切。多件卡波利瓦塞拉大头颅兽（<i>A. kapoliwacela</i>）的幼年个体标本，有助于阐明盖基兽科（Geikiidae）内部的个体发育趋势，包括不同盖基兽类物种间额后骨的发育与愈合模式差异。部分标本的獠牙上存在大面积磨蚀面，表明大头颅兽属（<i>Aulacephalodon</i>）的觅食行为以贴近基底的取食方式为主。