Vertebrate fossils have been known from South India's Cauvery Basin since the 1840s, but records of marine vertebrates from the late Albian to Turonian Karai Formation have been limited to a single set of ichthyosaur remains. Recent surface collecting and sieving of lower Cenomanian glauconitic mudstones has yielded the first ichthyosaur material reported in India over the last 140 years, as well as a diverse and previously unrecorded shark assemblage. The ichthyosaur material, including several teeth and vertebrae, is assigned to the sole described Cretaceous genus Platypterygius and to the species P. indicus (Lydekker, 1879). Eight species of shark (one squaliformes, two hexanchiformes, and five lamniformes) are recorded. A new hexanchiform genus Gladioserratus is erected, and two new species (Gladioserratus magnus, gen. et sp. nov., and Dwardius sudindicus, sp. nov.) are named. Many of the shark genera within this largely species-level endemic fauna are known from high paleolatitudes elsewhere, with many showing an antitropical distribution, but are absent in Tethyan areas. This first description of the Karai Formation marine fauna documents the previously unappreciated diversity and unique character of India's Cretaceous marine vertebrates, and indicates a cool-water paleoenvironment for the marine vertebrate assemblage.