REASSESSMENT OF THE SAUROPOD DINOSAURJAINOSAURUS (='ANTARCTOSAURUS') SEPTENTRIONALISFROM THE UPPER CRETACEOUS OF INDIA

摘要

Early evaluations of sauropod diversity in the Cretaceous of India recognized three genera,"Titanosaurus," Antarctosaurus, and Laplatasaurus, each of which was thought to have closelyrelated species on other southern landmasses. Recent systematic work has challenged the validityof the genus "Titanosaurus " and the supposed close relationship between its constituent species,particularly those from the Cretaceous of South America and Madagascar. Likewise, Laplatasau-rus is currently recognized to be restricted to South America, and the Indian species is invalid.Here, we redescribe the anatomy of the Indian sauropod species Antarctosaurus (now known asJainosaurus) septentrionalis with the goal of examining its validity, constituency, and phyloge-netic affinity. The type series ofJainosaurus septentrionalis included a braincase, skull roof, and many post-cranial elements that were united on the basis of their large size relative to the other taxon fromthe same quarry, "Titanosaurus indicus". All postcranIal bones were missing until recently, whenthe type series humerus and a cast of the scapula were riediscovtred in the collections of the In-dian Museum. We evaluate possible associations 44tiveen type series elements, bringing to lightcircumstantial evidence that helps strengthen the= fa far grouping some of them as a single spe-cies. Both the cranial and some postcranial bones,,ve,diagnostic, allowing referral of additionalmaterials collected from the same locality and elsewhere in lndo-Pakistan to the species J. septen-trionalis. Currently two genera, Isisaurus and Jainosaurus, are-recognized from the Cretaceous of India.Unlike most titanosaurs, both Isisaurus and Jainosaurus are known from diagnostic cranial andpostcranial material recorded from multiple localities. These genera coexist in central and westernIndia, and Isisaurus has been reported recently from western Pakistan. The affinities of Jaino-saurus and Isisaurus within Titanosauria are not yet resolved, but a sister-taxon relationship to oneanother can be ruled out. Jainosaurus appears to have close relatives in Madagascar and SouthAmerica based on the data at hand. Thus far, there is no evidence for an endemic Indian sauropodfauna during the Late Cretaceous.