Measurements of teeth.

Mass extinctions change the trajectory of evolution and restructure ecosystems. The largest mass extinction, the end-Permian, is a particularly interesting case due to the hypothesized delay in the recovery of global ecosystems, where total trophic level recovery is not thought to have occurred until 5–9 million years after the extinction event. Diapsids, especially archosauromorphs, play an important role in this recovery, filling niches left vacant by therapsids and anapsids. However, the nature of lineage and ecological diversification of diapsids is obscured by the limited number of continuous, well-dated stratigraphic sections at the Permian-Triassic boundary and continuing through the first half of the Triassic. The Karoo Basin of South Africa is one such record, and particularly the late Early Triassic (Olenekian) Driefontein locality fills this gap in the diapsid fossil record. We collected a total of 102 teeth of which 81 are identified as diapsids and the remaining 21 as identified as temnospondyls. From the sample, seven distinct tooth morphotypes of diapsids are recognized, six of which are new to the locality. We used a combination of linear measurements, 3D geomorphometrics, and nMDS ordination to compare these morphotypes and made inferences about their possible diets. Although the morphotypes are readily differentiated in nMDS, the overall morphological disparity is low, and we infer five morphotypes are faunivorous with the other two potentially omnivorous or piscivorous based on their morphological similarities with dentitions from extant diapsids, demonstrating an unsampled taxonomic and ecological diversity of diapsids in the Early Triassic based on teeth. Although ecological specialization at Driefontein may be low, it records a diversity of diapsid taxa, specifically of archosauromorph lineages.

生物大灭绝事件会改变演化轨迹并重塑生态系统。其中规模最大的二叠纪末大灭绝（end-Permian）尤为值得关注：此前学界提出全球生态系统恢复存在延迟现象，普遍认为全球营养级（trophic level）的完全恢复直至该灭绝事件发生后的500万至900万年才得以实现。
双孔类（diapsids），尤其是主龙形类（archosauromorphs），在此次生态系统恢复中发挥了重要作用，填补了兽孔类（therapsids）与无孔类（anapsids）遗留的生态位空缺。但由于二叠纪-三叠纪界线（Permian-Triassic boundary）及三叠纪早期前半段的连续、定年精准的地层剖面（stratigraphic sections）数量稀缺，双孔类的演化支系与生态多样化的本质仍较为模糊。
南非卡鲁盆地（Karoo Basin）正是这类记录之一，其中早三叠世晚期（奥伦尼克期，Olenekian）的德赖方廷（Driefontein）化石点恰好填补了双孔类化石记录的这一空白。本次研究共采集到102枚牙齿，其中81枚被鉴定为双孔类牙齿，剩余21枚则被归为离片椎类（temnospondyls）牙齿。经分析，本次样本中共识别出7种独立的双孔类牙齿形态型（tooth morphotypes），其中6种为该化石点首次报道。
我们结合线性测量（linear measurements）、三维几何形态测量学（3D geomorphometrics）与非度量多维标度排序（nMDS ordination）对这些形态型进行了比较，并据此推断其可能的食性。尽管通过nMDS排序可清晰区分各牙齿形态型，但整体形态差异度较低；结合现存双孔类的齿列形态相似性，我们推断其中5种形态型为食动物性，另外2种可能为杂食性或食鱼性。本次基于牙齿的研究表明，早三叠世双孔类存在此前未被采样记录的分类学与生态多样性。
尽管德赖方廷化石点的生态特化程度可能较低，但该位点记录了多样的双孔类类群，尤其是主龙形类演化支系。