Haldar Atrayee, Ray Sanghamitra
Department of Geology and Geophysics, Indian Institute of Technology Kharagpur, Kharagpur, India.
J Anat. 2025 Aug;247(2):223-249. doi: 10.1111/joa.14255. Epub 2025 Apr 9.
The Late Triassic Tiki fauna from India represents one of the richest and most diverse vertebrate faunal assemblages, essentially known for archosauromorphs, temnospondyls, fishes, lizards, and trace fossils like coprolites. In this paper, we provide a detailed morphological description of isolated lateral osteoderms from a multitaxic bonebed of the Tiki Formation. The osteoderms bear a spike-like eminence formed by two asymmetric flanges, radial ornamentation, and a thick, indented medial margin suggesting that these pertained to a pseudosuchian archosaur. With the purpose of demonstrating the internal anatomy, X-ray microCT was used to reveal a compact diploe structure with a highly vascularised core characterising most archosaurian osteoderms. Such a high degree of compactness with an internal vascular network and open vascular canals can be hypothesised to serve as protection from predation and for thermoregulation. A comparative study with different Late Triassic armoured archosauromorphs revealed morphological resemblance of the osteoderms to lateral osteoderms of desmatosuchine aetosaurs and the aetosauriform Acaenasuchus geoffreyi. A phylogenetic analysis comprising all the Late Triassic archosauromorphs placed the Tiki taxon within Aetosauriformes. However, an additional analysis including all aetosaurs positioned the new taxon deeply nested within Desmatosuchini as sister taxon to Desmatosuchus. Better understanding of the phylogenetic position can only be achieved by recovering more cranial and post-cranial materials. This contribution demonstrates the first occurrence of a Desmatosuchus-like taxon from the Tiki Formation and bolsters the significance of the horizon in global correlation and also contributes to our understanding of the dispersal of aetosaurs or similar taxa in different parts of Pangaea during the Late Triassic.
来自印度的晚三叠世提基动物群是最丰富、最多样化的脊椎动物群组合之一，主要以主龙形类、离片锥类、鱼类、蜥蜴以及粪化石等遗迹化石而闻名。在本文中，我们对提基组一个多分类骨床中分离出的外侧皮内成骨进行了详细的形态学描述。这些皮内成骨具有由两个不对称凸缘形成的尖状隆起、放射状纹饰以及厚且有凹痕的内侧边缘，表明它们属于伪鳄类主龙。为了展示内部解剖结构，我们使用X射线显微CT揭示了一种致密的板障结构，其核心高度血管化，这是大多数主龙类皮内成骨的特征。可以推测，这种具有内部血管网络和开放血管通道的高度致密性能够起到抵御捕食和调节体温的作用。与不同晚三叠世披甲主龙形类的比较研究表明，这些皮内成骨与坚蜥科坚蜥类以及坚蜥形类的杰氏阿氏龙的外侧皮内成骨在形态上相似。一项包含所有晚三叠世主龙形类的系统发育分析将提基分类单元置于坚蜥形目内。然而，另一项包括所有坚蜥的分析将这个新分类单元深深地嵌套在坚蜥科内，作为坚蜥的姐妹分类单元。只有通过获取更多的颅骨和颅后材料，才能更好地了解其系统发育位置。这一研究首次证明了提基组中存在类似坚蜥的分类单元，提升了该地层在全球对比中的重要性，也有助于我们理解晚三叠世坚蜥或类似分类单元在泛大陆不同地区的扩散情况。
