Fossorial tadpoles of Micrixalus herrei, having eel-like, dorsoventrally flattened bodies, dorsal eyes, and well-developed muscular tails with reduced fins, after being exposed from the sand and gravel bed. SD Biju

Scientists have discovered the hitherto unseen tadpoles of the Indian Dancing frog family from inside stream beds in the biodiversity hotspot of the Western Ghats. The tadpoles that live in total darkness beneath the sand till they develop into baby frogs are equipped especially for their chosen habitat. They inhabit sandy banks under canopy-covered streams.

Muscular bodies and early ribs help them burrow through sand while skin-covered eyes and serrated jaws prevent sand grains entering the eye or mouth. Small sand grains and decaying organic matter in its gut act as a nutrient source.

While the ancient and endemic Dancing Frogs family of the Micrixalidae has been seen and documented for their sexual display by way of waving legs, their tadpoles had not been seen before. The work by the scientists from University of Delhi, University of Peradeniya and Gettysburg College is published in the open-access journal PLOS ONE.

Prof. S D Biju from University of Delhi says, "We provide the first confirmed report of the tadpoles of Indian Dancing frog family. These tadpoles probably remained unnoticed all these years because of their fossorial nature, which in itself is a rare occurrence in the amphibian world."

The external morphology of the tadpoles and a scrutiny of their bones revealed the presence of ribs in very early stages of tadpoles. Prof. Madhava Meegaskumbura from University of Peradeniya states, "only four families of frogs are reported to have ribs, but we show that at least some of
Micrixalidae also have ribs, even as tadpoles; this adaptation may provide for greater muscle attachment, helping them wriggle through sand."

Whitish globular sacs storing calcium carbonate, known as "lime sacs," are present even in juvenile frogs of Micrixalus, which is uncommon in other frogs.

The new finding reiterates the uniqueness of amphibians of the Western Ghats biodiversity hotspot. Older than the Himalaya mountains, the mountain chain represents geomorphic features of immense importance with unique biophysical and ecological processes. According to the Unesco, it presents one of the best examples of the monsoon system on the planet and has an exceptionally high level of biological diversity and endemism. It is recognized as one of the world's eight 'hottest hotspots' of biological diversity.