Oklahoma State University, Tahlequah, OK, United States of America.
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.
PLoS One. 2024 Jan 24;19(1):e0294901. doi: 10.1371/journal.pone.0294901. eCollection 2024.
Caenagnathidae is a clade of derived, Late Cretaceous oviraptorosaurian theropods from Asia and North America. Because their remains are rare and often fragmentary, caenagnathid diversity is poorly understood. Anzu wyliei is the only caenagnathid species currently described from the late Maastrichtian Hell Creek Formation of the USA and is also among the largest and most completely preserved North American caenagnathids. Smaller, less complete caenagnathid material has long been known from the Hell Creek Formation, but it is unclear whether these are juvenile representatives of Anzu or if they represent distinct, unnamed taxa. Here, we describe a relatively small caenagnathid hindlimb from the Hell Creek Formation, and conduct osteohistological analysis to assess its maturity. Histological data and morphological differences from Anzu wyliei and other caenagnathids allow us to conclude that this specimen represents a new species of caenagnathid from the Hell Creek Formation, with a smaller adult body size than Anzu. This new taxon is also distinct from other small caenagnathid material previously described from the area, potentially indicating the coexistence of three distinct caenagnathid species in the Hell Creek Formation. These results show that caenagnathid diversity in the Hell Creek ecosystem has been underestimated.
伤齿龙科是一类衍生的、晚白垩世的兽脚亚目恐龙，来自亚洲和北美洲。由于它们的遗骸罕见且通常不完整，因此对伤齿龙科的多样性了解甚少。安祖兽是目前唯一一种被描述于来自美国晚马斯特里赫特期的地狱溪组的伤齿龙科物种，也是北美保存最完整、体型最大的伤齿龙科恐龙之一。较小的、不太完整的伤齿龙科材料长期以来一直存在于地狱溪组中，但尚不清楚这些是否是安祖兽的幼年代表，或者它们是否代表不同的、未命名的分类单元。在这里，我们描述了一个来自地狱溪组的相对较小的伤齿龙科后肢，并进行了骨组织学分析以评估其成熟度。组织学数据和与安祖兽及其他伤齿龙科的形态差异使我们得出结论，该标本代表了来自地狱溪组的伤齿龙科的一个新种，其成年体型比安祖兽小。这个新分类群也与该地区以前描述的其他小型伤齿龙科材料不同，可能表明在地狱溪组中存在三种不同的伤齿龙科物种的共存。这些结果表明，在地狱溪生态系统中伤齿龙科的多样性被低估了。
