A new bird-like dinosaur from the Upper Cretaceous of Mongolia with extremely robust hands supports niche partitioning among velociraptorines

Dromaeosauridae is a clade of bird-like theropod dinosaurs including, among others, the genera <i>Deinonychus</i> and <i>Velociraptor</i>, and characterised by a specialised second toe bearing an enlarged and falciform ungual. Here, we describe an exquisitely-preserved velociraptorine dromaeosaurid from the Upper Cretaceous Djadokhta Formation of Mongolia, and refer it to the new species <i>Shri rapax</i>. This dromaeosaurid is diagnosed by a peculiar combination of vertebral and pelvic features and by an exceptionally robust hand with a very stout pollex bearing the ungual proportionally larger than in any other dromaeosaurid. Combined with cranial adaptations which could support a bite more powerful than in other velociraptorines, the enlarged unguals in both <i>Shri</i> species suggest ecological partitioning in prey preference among the sympatric Djadokhtan dromaeosaurids.

驰龙科（Dromaeosauridae）是一类似鸟类兽脚类恐龙演化支，涵盖恐爪龙属（*Deinonychus*）、伶盗龙属（*Velociraptor*）等类群，以特化的第二趾具膨大且镰刀状爪骨（ungual）为典型鉴别特征。本文记述了一件产自蒙古国上白垩统德加多克塔组（Upper Cretaceous Djadokhta Formation）的保存极为精美的伶盗龙亚科驰龙科化石，并将其归入新种*Shri rapax*。该驰龙科物种的鉴定特征为椎体与骨盆特征的独特组合，以及异常粗壮的手部：其第一指（pollex）极为强健，所附爪骨的比例远超其他所有驰龙科类群。结合其头骨适应性特征——可支撑强于其他伶盗龙亚科成员的咬合力——，两种*Shri*属物种的膨大爪骨表明，同域分布于德加多克塔组的驰龙科类群之间存在基于猎物偏好的生态位分化。