Paleontology, North Carolina Museum of Natural Sciences, Raleigh, North Carolina, United States of America.
Department of Biological Sciences, North Carolina State University, Raleigh, North Carolina, United States of America.
PLoS One. 2023 Jun 7;18(6):e0286042. doi: 10.1371/journal.pone.0286042. eCollection 2023.
Intensifying macrovertebrate reconnaissance together with refined age-dating of mid-Cretaceous assemblages in recent decades is producing a more nuanced understanding of the impact of the Cretaceous Thermal Maximum on terrestrial ecosystems. Here we report discovery of a new early-diverging ornithopod, Iani smithi gen. et sp. nov., from the Cenomanian-age lower Mussentuchit Member, Cedar Mountain Formation of Utah, USA. The single known specimen of this species (NCSM 29373) includes a well-preserved, disarticulated skull, partial axial column, and portions of the appendicular skeleton. Apomorphic traits are concentrated on the frontal, squamosal, braincase, and premaxilla, including the presence of three premaxillary teeth. Phylogenetic analyses using parsimony and Bayesian inference posit Iani as a North American rhabdodontomorph based on the presence of enlarged, spatulate teeth bearing up to 12 secondary ridges, maxillary teeth lacking a primary ridge, a laterally depressed maxillary process of the jugal, and a posttemporal foramen restricted to the squamosal, among other features. Prior to this discovery, neornithischian paleobiodiversity in the Mussentuchit Member was based primarily on isolated teeth, with only the hadrosauroid Eolambia caroljonesa named from macrovertebrate remains. Documentation of a possible rhabdodontomorph in this assemblage, along with published reports of an as-of-yet undescribed thescelosaurid, and fragmentary remains of ankylosaurians and ceratopsians confirms a minimum of five, cohabiting neornithischian clades in earliest Late Cretaceous terrestrial ecosystems of North America. Due to poor preservation and exploration of Turonian-Santonian assemblages, the timing of rhabdodontomorph extirpation in the Western Interior Basin is, as of yet, unclear. However, Iani documents survival of all three major clades of Early Cretaceous neornithischians (Thescelosauridae, Rhabdodontomorpha, and Ankylopollexia) into the dawn of the Late Cretaceous of North America.
几十年来，加强对大型脊椎动物的侦察以及对白垩纪中期组合的精细测年，正在使我们更深入地了解白垩纪热极值对陆地生态系统的影响。在这里，我们报告了一种新的早期分化的鸟脚类恐龙——Iani smithi gen. et sp. nov. 的发现，它来自美国犹他州的Cedar Mountain Formation 的 Cenomanian 时代下部 Mussentuchit 成员。这个物种的唯一已知标本（NCSM 29373）包括一个保存完好的、脱节的头骨、部分轴柱和附肢骨骼的部分。特化特征集中在额骨、鳞状骨、脑壳和前颌骨上，包括存在三个前颌齿。使用简约法和贝叶斯推断的系统发育分析将 Iani 置于北美 rhabdodontomorph 中，基于存在增大的、桨状的牙齿，具有多达 12 个次生脊，上颌齿没有初级脊，颧骨的上颌骨突起侧向凹陷，以及后颞孔仅限于鳞状骨，以及其他特征。在此发现之前，Mussentuchit 成员中的 neornithischian 古生物多样性主要基于孤立的牙齿，只有鸭嘴龙类的 Eolambia caroljonesa 是从大型脊椎动物遗骸中命名的。在这个组合中发现的可能的 rhabdodontomorph，以及发表的尚未描述的厚头龙科恐龙和甲龙类和角龙类的碎片遗骸，证实了在北美最早的晚白垩世陆地生态系统中至少有五个共存的 neornithischian 分支。由于 Turonian-Santonian 组合的保存和探索不佳，rhabdodontomorph 在西部内陆盆地的灭绝时间目前尚不清楚。然而，Iani 记录了早白垩世 neornithischian 三大分支（厚头龙科、雷龙形类和甲龙类）在北美晚白垩世黎明时期的生存。
