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Indohyus Indohyus

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Indohyus ("India's pig") is a genus of extinct artiodactyl known from Eocene fossils in Asia, purported to be approximately 48 million years old. A December 2007 article in Nature by Thewissen et al. using an exceptionally complete skeleton of Indohyus from Kashmir indicates that raoellids may be the "missing link" sister group to whales (Cetacea). All other Artiodactyla are "cousins" of these two groups. δ18O values and osteosclerotic bones indicate that the raccoon-like or chevrotain-like Indohyus was habitually aquatic, but δ13C 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. Location: Kashmir, India Age: Middle Eocene; 48 million years ago Indohyus belongs to an early radiation of artiodactyl mammals called raoellids, archaic even-toed hoofed mammals known mostly from teeth and found only in Eocene southern Asia. Indohyus is known from a partially-complete skeleton, which reveals peculiar features. It is about the size of a fox with heavy leg bones. These features are largely used by limbed mammals that spend time in water, using the heavy legs to weigh down the animal to counteract natural boyancy. This means Indohyus could live a life not unlike that of a modern water mousedeer, diving underwater to escape predators or to eat water plants. Its most interesting feature of all is its ear contains a large bone surrounding its middle ear, a feature seen only in

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Indohyus

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Indohyus major

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* I. indirae * I. major

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(Rao, 1971) Indohyus

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Mammalia

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?Raoellidae

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Indohyus ("India's pig") is a genus of extinct artiodactyl known from Eocene fossils in Asia, purported to be approximately 48 million years old. A December 2007 article in Nature by Thewissen et al. using an exceptionally complete skeleton of Indohyus from Kashmir indicates that raoellids may be the "missing link" sister group to whales (Cetacea). All other Artiodactyla are "cousins" of these two groups. δ18O values and osteosclerotic bones indicate that the raccoon-like or chevrotain-like Indohyus was habitually aquatic, but δ13C 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. The fossils were discovered among rocks that had been collected more than 30 years ago in Kashmir by the Indian geologist A Ranga Rao who found a few teeth and parts of a jawbone, but when he died many rocks had yet to be broken open. Ranga Rao's widow gave the rocks to Professor Thewissen, who was working on them when his technician accidentally broke one of the skulls they had found and Thewissen recognised the ear structure of the auditory bulla, formed from the ectotympanic bone in a shape which is highly unusual and only resembles the skulls of whales and the earlier land creature Pakicetus. However, not all paleontologists are firmly persuaded that Indohyus is the transitional fossil that cetacean-origin experts were looking for. ScienceNOW, a daily news feature of the journal Science, notes that a team set to publish in the journal Cladistics postulates an extinct group of carnivorous mammals called "mesonychids" as more closely related to cetaceans. Additionally, the ScienceNOW article notes that "cetaceans are so different from any other creature that researchers haven’t been able to agree which fossil relatives best represent their nearest ancestors." About the size of a raccoon or domestic cat, this herbivorous deer-like creature shared some of the traits of whales, and showed signs of adaptations to aquatic life, including a thick and heavy outer coating to bones which is similar to the bones of modern creatures such the hippopotamus, and reduces buoyancy so that they can stay underwater. This suggests a similar survival strategy to 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. Location: Kashmir, India Age: Middle Eocene; 48 million years ago Indohyus belongs to an early radiation of artiodactyl mammals called raoellids, archaic even-toed hoofed mammals known mostly from teeth and found only in Eocene southern Asia. Indohyus is known from a partially-complete skeleton, which reveals peculiar features. It is about the size of a fox with heavy leg bones. These features are largely used by limbed mammals that spend time in water, using the heavy legs to weigh down the animal to counteract natural boyancy. This means Indohyus could live a life not unlike that of a modern water mousedeer, diving underwater to escape predators or to eat water plants. Its most interesting feature of all is its ear contains a large bone surrounding its middle ear, a feature seen only in whales. The same feature also appears in Pakicetus as well. The presence of an encased middle ear in an artiodactyl shows further evidence of whales being descendents of land-based hoofed mammals like pigs and antelope. However because it existed after many early whales are known, Indohyus could not be an ancestor of whales but it could share an ancestor with them. Resources: