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Jainosaurus (Jain's lizard) is a large titanosaurian dinosaur of India and wider Asia, which lived in the Maastrichtian (approximately 68 mya).

The first remains were between 1917 and 1920 found by Charles Alfred Matley near Jabalpur in the Lameta Formation. These were named Antarctosaurus septentrionalis by Friedrich von Huene and Matley in 1933.[1] The specific name means "northern" in Latin, a reference to the fact that the species was discovered on the Northern hemisphere whereas Antarctosaurus means "saurian from the Southern hemisphere" because its type species Antarctosaurus wichmannianus was found in Argentina.

In 1995 Adrian Paul Hunt e.a. named a separate genus: Jainosaurus.[2] The generic name honours the Indian paleontologist Sohan Lal Jain,[3] who worked on the cranial nerve impressions in the skull;[4] and in 1982 published a study about the results.[5] Ironically Jain himself considers this species to be likely identical to Titanosaurus indicus, found in the same formation and named in 1877, which would make Jainosaurus septentrionalis a younger synonym.[6] He believes that the remains represent merely a young or female Titanosaurus.

In 2009 a detailed redescription by Jeffrey Wilson e.a. chose GSI IM K27/497, a braincase (basicranium) as the lectotype. The postcrania, which had been assumed lost, were shown to be largely present in the collection of the Geological Survey of India at Calcutta. They include: dorsal rib fragments (GSI K20/326, K27/425); a caudal vertebra (GSI K20/317), four chevrons (GSI K27/492–494, 496), the left and right scapula (only a cast still extant); a sternal plate (GSI K20/647); a humerus (lacking an inventory number), a radius (GSI K27/490) and an ulna (GSI K27/491). In 1996 Sankar Chatterjee referred a second braincase to the species: ISI R162. Some material from Pakistan also possibly belongs to Jainosaurus

A herbivorous quadruped, an adult Jainosaurus would have measured around eighteen metres long and held its head six metres high. No accurate estimate of the weight has yet been made. The humerus of the type specimen is 134 centimetres long.

Wilson e.a. concluded that Jainosaurus is a valid taxon, clearly distinguishable from Isisaurus. It would have been a fairly derived member of the Titanosauria, more closely related to South-American forms like Pitekunsaurus, Muyelensaurus and Antarctosaurus than to Isisaurus or Rapetosaurus.[7]