Читать книгу Hadrosaurs - David A. Eberth - Страница 112

The Djadokhta Formation (Campanian) has been intensely surveyed and sampled for its fossil vertebrate fauna for almost a century. Its dinosaur fauna is historically defined as being dominated by the ornithischians Protoceratops and Pinacosaurus, as well as oviraptorid theropods, but recent collecting efforts continue to yield new taxa. Here we describe and name the first ornithopod from this unit. The material consists of an almost complete skull and associated limb material collected from the Alag Teeg locality. Plesiohadros djadokhtaensis nov. gen. et nov. sp. is characterized by a unique combination of plesiomorphic and derived characters within Hadrosauroidea, and an autapomorphically rugose, raised rim around the rostrodoral margin of the orbit. In order to place P. djadokhtaensis into its paleoecological and stratigraphic context within these Upper Cretaceous rocks of Mongolia, we also provide a review of the geological setting of the Djadokhta Formation in the Gobi Desert. Plesiohadros is the largest member of the Djadokhta fauna, and the only known hadrosauroid from the Campanian of Mongolia. An updated phylogenetic analysis indicates that P. djadokhtaensis is a derived hadrosauroid proximate to Hadrosauridae (sensu Sereno). Plesiohadros is posited as the sister taxon to a clade that includes Lophorhothon and Hadrosauridae, and is more closely related to Hadrosauridae than to Bactrosaurus, Telmatosaurus, or Tethyhadros. The complete replacement of non-hadrosaurid hadrosauroids with true hadrosaurids in the Maastrichtian of Mongolia highlights the complex pattern of faunal interchange between Asian and North America in the latest Cretaceous.