Mooney Ethan Dean, Scott Diane, Reisz Robert Raphael
Department of Biology, University of Toronto Mississauga, 3359 Mississauga Rd., Mississauga, ON L5L1C6 Canada.
Dinosaur Evolution Research Center, International Center of Future Science, Jilin University, 2699 Qianjin Str., Changchun, 130012 Jilin China.
Swiss J Palaeontol. 2025;144(1):10. doi: 10.1186/s13358-025-00351-y. Epub 2025 Feb 26.
The evolutionary radiation of diapsid reptiles that includes all extant and most extinct reptiles is well-represented in the Mesozoic and Cenozoic fossil records, however, the earliest stages recorded in the Paleozoic Era are limited to comparatively few taxa. Consequently, the origins of Sauria, the crown-group of Diapsida, remains poorly understood and the phylogenetic positions of the few known taxa along the saurian stem are controversial. Here, we describe sp. et gen. nov., a new early late Permian stem saurian from the Karoo of South Africa based on two skulls and show that the famous aggregation of "juvenile " SAM-PK-K7710 is also referrable to it, thereby making this one of the best-known stem saurians. The skull has a short rostrum, open lower temporal bar, large contribution of the postfrontal to the upper temporal fenestra, slender stapes, sliver-like supratemporal with a distinct lateral flange suturing to the postorbital, and lacks both postparietal and tabular bones. The saddle-shaped quadrate is rather saurian-like in being posteriorly emarginated with a tympanic crest and unique medial flange. The post cranial skeleton of is lizard-like and notably shows a hook-shaped fifth metatarsal and thyroid fenestra. Phylogenetic analysis recovers as sister to Sauria, which is especially surprising considering its rather small size and slender, lizard-like morphology prior to the split between the apparently similar lepidosauromorphs and many of the comparatively robust archosauromorph saurians. Our analysis also indicates that falls outside the clade of + Sauria and does not appear to form a clade with other "younginiform" reptiles. The available evidence indicates a surprising level of complexity related to the evolution of stem saurians and the origin of Sauria that occurred in the shadow of other Paleozoic amniotes.
The online version contains supplementary material available at 10.1186/s13358-025-00351-y.
双孔亚纲爬行动物的进化辐射涵盖了所有现存和大多数已灭绝的爬行动物，在中生代和新生代化石记录中得到了很好的体现，然而，古生代记录的最早阶段仅限于相对较少的类群。因此，双孔亚纲的冠群——蜥蜴亚目（Sauria）的起源仍知之甚少，沿着蜥蜴亚目演化支的少数已知类群的系统发育位置也存在争议。在这里，我们基于两个头骨描述了一种来自南非卡鲁地区的新的二叠纪晚期早期蜥蜴亚目演化支物种及新属，并且表明著名的“幼年”标本SAM-PK-K7710的聚合体也可归属于它，从而使其成为最著名的蜥蜴亚目演化支物种之一。该头骨有一个短吻部、开放的下颞弓、额后骨对上颞孔有很大贡献、镫骨细长、鳞片状的颞上骨有一个明显的侧向凸缘与眶后骨缝合，并且没有顶后骨和板骨。鞍形的方骨在后部有缺刻，有一个鼓膜嵴和独特的内侧凸缘，相当类似蜥蜴亚目。的颅后骨骼类似蜥蜴，特别显示出一个钩形的第五跖骨和甲状孔。系统发育分析将恢复为蜥蜴亚目的姐妹群，考虑到它在明显相似的鳞龙形类和许多相对粗壮的主龙形类蜥蜴亚目之间分裂之前相当小的体型和细长的、类似蜥蜴的形态，这尤其令人惊讶。我们的分析还表明，落在+蜥蜴亚目的分支之外，并且似乎没有与其他“杨氏蜥形类”爬行动物形成一个分支。现有证据表明，与在其他古生代羊膜动物的阴影下发生的蜥蜴亚目演化支的进化和蜥蜴亚目的起源相关的复杂性达到了惊人的程度。
在线版本包含可在10.1186/s13358-025-00351-y获取的补充材料。
