Reassessment of the sauropod dinosaur Jainosaurus (= "Antarctosaurus") septentrionalis from the Upper Cretaceous of India

Early evaluations of sauropod diversity in the Cretaceous of India recognized three genera, “Titanosaurus,” Antarctosaurus, and Laplatasaurus, each of which was thought to have closely related species on other southern landmasses. Recent systematic work has challenged the validity of the genus “Titanosaurus” and the supposed close relationship between its constituent species, particularly those from the Cretaceous of South America and Madagascar. Likewise, Laplatasaurus 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 as Jainosaurus) septentrionalis with the goal of examining its validity, constituency, and phylogenetic affinity. The type series of Jainosaurus septentrionalis included a braincase, skull roof, and many postcranial elements that were united on the basis of their large size relative to the other taxon from the same quarry, “Titanosaurus indicus”. All postcranial bones were missing until recently, when the type series humerus and a cast of the scapula were rediscovered in the collections of the Indian Museum. We evaluate possible associations between type series elements, bringing to light circumstantial evidence that helps strengthen the case for grouping some of them as a single species. Both the cranial and some postcranial bones are diagnostic, allowing referral of additional materials collected from the same locality and elsewhere in Indo-Pakistan to the species J. septentrionalis. 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 and postcranial material recorded from multiple localities. These genera coexist in central and western India, and Isisaurus has been reported recently from western Pakistan. The affinities of Jainosaurus and Isisaurus within Titanosauria are not yet resolved, but a sister-taxon relationship to one another can be ruled out. Jainosaurus appears to have close relatives in Madagascar and South America based on the data at hand. Thus far, there is no evidence for an endemic Indian sauropod fauna during the Late Cretaceous. Contributions from the Museum of Paleontology, University of Michigan 1Museum of Paleontology and Department of Geological Sciences, University of Michigan, 1109 Geddes Avenue, Ann Arbor, Michigan 48109–1079, U.S.A. (wilsonja@umich.edu; mdemic@umich.edu) 2Biology and Geology Departments, Macalester College, 1600 Grand Avenue, St. Paul, Minnesota 55105, U.S.A. (rogersk@macalester.edu) 3Palaeontology Division, Geological Survey of India (Central Region), Seminary Hills, Nagpur 440 010, India (dinomohabey@yahoo.com) 4Curatorial Division, Geological Survey of India (Central Headquarters), 27 Jawaharlal Nehru Road, Kolkata 700 016, India (ssen84@gmail.com) 18 J. A. WIlSon ET Al. Richard Lydekker and Friedrich von Huene made lasting contributions to the study of Indian and South American dinosaurs as a result of their successive surveys of two important collections in the late nineteenth and early twentieth centuries. Their taxonomic decisions, one of which is discussed in detail here, helped to shape the understanding of Indian and South American dinosaur faunas and their relationship to one another. In addition to describing some of the first dinosaurs from these landmasses, Lydekker and Huene independently asserted that India, South America, and Madagascar shared common titanosaur sauropod genera that evidenced a “remarkable community of type which undoubtedly exists between the faunas of southern continents of the world” (Lydekker, 1893: 3). The idea that titanosaurs were Gondwanan in origin and distribution persisted until quite recently (e.g., Bonaparte, 1999), but has given way to the current understanding of titanosaurs as a speciose (50+ genera), globally distributed clade that originated prior to the breakup of Pangea (e.g., Upchurch et al., 2004; Curry Rogers, 2005). Nevertheless, the interrelationships amongst titanosaurs from southern landmasses remains a key issue for Gondwanan paleobiogeography. Resolving the validity, constituency, and affinities of Gondwanan titanosaur genera is the first step in this process. Lydekker, who specialized in fossil and recent mammals, served on the Geological Survey of India in Calcutta (now Kolkata) from 1874–1882 (Thomas, 1917). During his residence in India, Lydekker produced several volumes in Palaeontologia Indica describing “Indian Tertiary and Pre-Tertiary Vertebrata”, continuing a tradition started by Huxley in the 1840s. Among the many fossils he described were the tail vertebrae of India’s first dinosaurs, the sauropods “Titanosaurus indicus” and “T. blanfordi” from Cretaceous beds of Bara Simla (Lydekker, 1877, 1879; Fig. 1). After returning to England and cataloguing the fossil tetrapods of the British Museum (Natural History), Lydekker was invited to describe the fossil mammal collections in the provincial museum in La Plata, Argentina, visiting twice between 1893 and 1894 (Anonymous, 1896). There, Lydekker described new sauropod dinosaurs as well, including two species of “Titanosaurus” (“T.” australis, “T.” nanus) and the genera and species Argyrosaurus superbus and Microcoelus patagonicus (Lydekker, 1893). Huene was a generation younger than Lydekker and specialized in fossil reptiles. Like Lydekker, Huene was invited to describe fossil collections of the Geological Survey of India and of the Museo de La Plata in Argentina. Huene visited Argentina between 1923 and 1926 to study collections in La Plata and Buenos Aires. In La Plata, he revised the collection of bones that Lydekker (1893) studied and divided specimens allocated to “T. ” australis into the new species “T. ” robustus and the new genus and species Laplatasaurus araukanicus (Huene, 1929: 48, 53). At the Museo Argentino de Ciencias Naturales in Buenos Aires, Huene studied a partial skull and postcranial bones from Patagonia that he named Antarctosaurus wichmannianus after their southern provenance and discoverer (Huene, 1929: 66). Although Huene apparently never visited India, he was able to study Charles Matley’s collection of Indian dinosaur bones whilst they were at the British Museum (Natural History) in the 1930s (Carrano et al., in press). In their monograph describing that collection, Huene and Matley (1933) described new species belonging to genera that Huene described from South America, Delhi