Indohyus

Indohyus (Meaning "India's pig" from the Greek words Indos, "from India" and hûs, "pig") is an extinct genus of artiodactyl known from Eocene fossils in Asia. This small chevrotain-like animal found in the Himalayas is among the closest known non-cetacean relatives of whales.^[1]

Indohyus Temporal range: Ypresian, 50–48 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Life restoration of Indohyus major
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Suborder:	Whippomorpha
Family:	†Raoellidae
Genus:	†Indohyus Rao, 1971
Species
†I. indirae †I. major?

Discovery

The fossils were discovered among rocks that had been collected in 1971 in Kashmir by the Indian geologist A. Ranga Rao who found a few teeth and parts of a jawbone;^[2] when he died, however, many rocks had yet to be broken open. Ranga Rao's widow gave the rocks to Hans Thewissen, who was working on them. When his technician accidentally broke one of the skulls they had found, Thewissen recognised the ear structure of the auditory bulla, formed from the ectotympanic bone in a shape which is highly distinctive, found only in the skulls of cetaceans both living and extinct, including Pakicetus.^[3]

Indohyus and raccoon skulls showing the ear structure of the auditory bulla

Paleobiology

About the size of a fox, this omnivorous pig-like creature shared some of the traits of whales, and showed signs of adaptations to aquatic life.^[4] Their bones were similar to the bones of modern creatures such as the hippopotamus, and helped reduce buoyancy so that they could stay underwater.^[5] This suggests a survival strategy similar to that of the African mousedeer or water chevrotain which, when threatened by a bird of prey, dives into water and hides beneath the surface for up to four minutes.^[3][6]

Classification

Raoellids may be the "missing link" sister group to whales (Cetacea).^[7] Oxygen-18 values and osteosclerotic bones indicate that the raccoon-like or chevrotain-like Indohyus was habitually aquatic, but ¹³C values suggest that it rarely fed in the water. The authors suggest this documents an intermediate step in the transition back to water completed by the whales, and suggests a new understanding of the evolution of cetaceans.^[8][9]

See also

• Pakicetus
• Evolution of cetaceans