A new hadrosauroid (Dinosauria: Ornithopoda) from the Late Cretaceous Baynshire Formation of the Gobi Desert (Mongolia)

A new genus and species of non-hadrosaurid hadrosauroid, Gobihadros mongoliensis, is described from a virtually complete and undeformed skull and postcranial skeleton, as well as extensive referred material, collected from the Baynshire Formation (Cenomanian-Santonian) of the central and eastern Gobi Desert, Mongolia. Gobihadros mongoliensis is the first non-hadrosaurid hadrosauroid from the Late Cretaceous of central Asia known from a complete, articulated skull and skeleton. The material reveals the skeletal anatomy of a proximate sister taxon to Hadrosauridae in remarkable detail. Gobihadros is similar to Bactrosaurus johnsoni and Gilmoreosaurus mongoliensis, but can be distinguished from them in several autapomorphic traits, including the maximum number (three) of functional dentary teeth per tooth position, a premaxillary oral margin with a ‘double-layer morphology’, and a sigmoidal dorsal outline of the ilium with a well-developed, fan-shaped posterior process. All of these characters in Gobihadros are inferred to be convergent in Hadrosauridae. Phylogenetic analysis positions Gobihadros mongoliensis as a Bactrosaurus-grade hadrosauromorph hadrosauroid. Its relationship with Maastrichtian hadrosaurids from Asia (e.g., Saurolophus angustirostris, Kerberosaurus manakini, Wulagasaurus dongi, Kundurosaurus nagornyi) are sufficiently distant to indicate that these latter taxa owe their distribution to migration from North America across Beringia, rather than having a common Asian origin with Go. mongoliensis.本次研究记述了一类全新的非鸭嘴龙科鸭嘴龙超科类群——蒙古戈壁龙（Gobihadros mongoliensis），其化石材料包含一件近乎完整且未受变形的头骨与颅后骨骼，另有大量归入标本，采集自蒙古国戈壁沙漠中部与东部的拜恩谢尔组（Baynshire Formation），地质时代为森诺曼期-桑托期（Cenomanian-Santonian）。蒙古戈壁龙是首个发现于中亚晚白垩世、以完整关联保存的头骨与骨骼为研究依据的非鸭嘴龙科鸭嘴龙超科类群。该化石材料以极高的细节精度，揭示了鸭嘴龙科近缘姐妹群的骨骼解剖学特征。戈壁龙属与约翰森巴克龙（Bactrosaurus johnsoni）和蒙古吉尔摩龙（Gilmoreosaurus mongoliensis）形态相近，但可通过多项自衍征与之区分：包括单个齿位的功能性齿最大数量可达3枚、前上颌骨的口腔缘呈现“双层形态”，以及髂骨背侧呈乙字形轮廓且带有发育良好的扇形后突。上述所有特征均被推断为与鸭嘴龙科存在趋同演化。系统发育分析显示，蒙古戈壁龙属于巴克龙级别的鸭嘴龙形类鸭嘴龙超科类群。它与亚洲马斯特里赫特期的鸭嘴龙科类群（如窄吻栉龙（Saurolophus angustirostris）、凯伯龙（Kerberosaurus manakini）、董氏乌拉嘎龙（Wulagasaurus dongi）、昆杜鲁斯龙（Kundurosaurus nagornyi））的亲缘关系较远，这表明后者的地理分布源自通过白令陆桥从北美迁徙而来，而非与蒙古戈壁龙共享共同的亚洲起源。