A new paratypothoracin aetosaur (Archosauria: Pseudosuchia) from the Upper Triassic Dharmaram Formation of India and its biostratigraphic implications

The Upper Triassic lower Dharmaram Formation of India has yielded a highly diverse archosaur-dominated fauna that included a paratypothoracin aetosaur <i>Venkatasuchus armatum</i>, a plateosaurian sauropodomorph <i>Jaklapallisaurus asymmetrica</i>, a neotheropod, and a Mystriosuchinae phytosaur. In this current contribution, we describe a new paratypothoracin aetosaur taxon, <i>Kuttysuchus minori</i> gen. et sp. nov., from the same horizon based on several isolated paramedian osteoderms recovered from a single fossil locality. These osteoderms are characterized by a weakly raised anterior bar with a short pointed anteromedial edge, deeply incised dorsal surface ornamentation composed of strongly radial pattern of ridges and grooves with a low density of pits surrounding a pointed pyramidal dorsal eminence placed near the posterior margin and a weakly developed ventral strut or transverse thickening. These features show similarity of the specimens to that of both <i>Paratypothorax</i> and <i>Stagonolepis olenkae</i> and strongly differentiate <i>Kuttysuchus</i> from the other paratypothoracin <i>Venkatasuchus</i> known from the same stratigraphic unit<i>.</i> Our phylogenetic analysis recovered <i>Kuttysuchus</i> as an early-diverging taxon within the clade Paratypothoracini. The rich record of paratypothoracin aetosaurs, along with that of a mystriosuchine phytosaur positively suggests a mid-to-late Norian age, though the age could be extended to the Rhaetian as suggested by previous studies. The current study considerably enhances knowledge of aetosaur diversity during the Late Triassic, particularly on Gondwana, and raises the potential of recovering a rich Gondwanan record of Paratypothoracini in future.

印度上三叠统下达摩拉姆组产出了以主龙类为优势类群的高度多样动物群，其中包含链鳄类（aetosaur）副盾鳄亚科（Paratypothoracini）的武装文卡特斯鳄（Venkatasuchus armatum）、板龙类蜥脚形亚目不对称雅克拉帕利龙（Jaklapallisaurus asymmetrica）、新兽脚类以及迷鳄亚科（Mystriosuchinae）植龙类（phytosaur）。本研究基于单个化石点采集的多件孤立次中骨板（paramedian osteoderms），对产自同一层位的副盾鳄亚科链鳄类新属新种小型库蒂鳄（Kuttysuchus minori gen. et sp. nov.）进行了描述。该类骨板的特征为：前缘脊弱发育，前内侧边缘短而尖锐；背表面纹饰深陷，由稀疏分布的坑点环绕着放射状脊沟构成，尖锐的锥状背隆靠近后缘，且腹侧支柱或横向增厚结构发育较弱。这些特征表明，该标本与副盾鳄属（Paratypothorax）及奥伦卡斯塔哥诺龙（Stagonolepis olenkae）具有相似性，同时可将库蒂鳄属与产自同一地层单元的另一副盾鳄亚科类群文卡特斯鳄清晰区分开来。本研究的系统发育分析（phylogenetic analysis）结果显示，库蒂鳄属属于副盾鳄亚科演化支下的早期分化类群。副盾鳄亚科链鳄类与迷鳄亚科植龙类的丰富化石记录，共同指示该地层的时代为诺利克期中晚期，不过既往研究也曾提出其时代可延伸至瑞替期。本研究极大丰富了晚三叠世，尤其是冈瓦纳大陆的链鳄类多样性认知，并为未来发现更多副盾鳄亚科的冈瓦纳化石记录提供了可能性。