Monsters and strange animals have, like in many places around the world, been reported in and around India for thousands of years. A particular type of sea monster, known in the west as Ketea Indikoi (literally 'Indian sea-monsters'), was reported to inhabit the Indian Ocean near Sri Lanka. The monsters supposedly could be encountered in a variety of forms, usually with the head of one animal and the body of a fish. The animals' heads were often said to be mammalian ones ranging from lions to rams, but as well as these there were claims that some even had the heads of women with spines instead of hair. The creatures are also said to have been able to live on land as well as in the oceans.
The animals, if they existed at all, were likely just the result of travellers distorting descriptions of perfectly normal animals found in the area, like large crocodiles. The most well known description of these creatures dates back to the second century AD in the part fable, part natural history work, De Natura Animalium (On the nature of animals) by Claudius Aelianus, which is based on reports that would have passed through many different people before reaching his ears.
'Those [Indians of Taprobane--\ modern day Sri Lanka] that live near to the sea . . . devote themselves to catching fish and sea-monsters (ketoi). For they assert that the sea which surrounds the circuit of their island breeds a multitude past numbering of fishes and monsters, and moreover that they have the heads of lions and leopards and wolves and rams, and, still more wonderful to relate, that there are some which have the forms of Satyroi with the faces of women, and these have spines attached in place of hair. They tell of others too which have strange forms whose appearance not even men skilled in painting and in combining bodies of diverse shapes to make one marvel at the sight, could portray with accuracy or represent for all of their artistic skill; for these creatures have immense and coiling tails, while for feet they have claws or fins. I learn too that they are amphibious and that at night they graze the fields, for they eat the grass as cattle and rooks do; they enjoy the ripe fruit of the date-palm and therefore shake the trees with their coils, which being supple and capable of embracing, they fling round them. So when the shower of dates has fallen because of this violent shaking, they feed upon it. And then as the night wanes and before it is clear daylight these creatures plunge into the ocean and disappear as the dawn begins to glow.'
Make of that what you will....