Land Dwelling Potential Ancestor of Whales Described

Researchers at the North-eastern Ohio Universities Colleges of Medicine and Pharmacy have published a paper on a land dwelling animal that shows links to the ancestry of whales.  The discovery of this animal could possibly provide evidence of a missing link in how terrestrial animals adapted to a marine existence.

Scientists have speculated that the ancestor of whales (cetaceans) was probably a carnivore with the otter-like Ambulocetus from the Eocene being a strong contender.  Ambulocetus means “walking whale” , the remains of this animal, which could reach lengths of 3 metres or more, have been found in Pakistan, now a new fossil from Kashmir, provides further insight into the evolution of modern whales.

This new fossil, which was actually unearthed 30 years previously, but has only recently been studied closely, is of a small deer-like animal, about the size of a large domestic cat, that roamed the dense rain-forests of Kashmir around 48 million years ago.  It had been thought that the ancestors of whales had adapted to a life in water as they hunted fish or became waterside ambush predators similar to crocodiles.  However, this little animal was definitely herbivorous, perhaps taking to an aquatic lifestyle to munch on lush water plants much as rodents like the South American Capybara do today.

This little animal has been named Indohyus,  although the skeleton is not complete the skull has been found and the preserved middle ear structure is identical to that found in the cetacean group.  Isotope analysis of the teeth is a little ambiguous, but has led to speculation that this animal was probably a herbivore and that it may have fed in water, although another interpretation of this data would conclude that Indohyus probably fed on land but spent a lot of time in an aquatic environment.

An Artists Impression of Indohyus

Picture Credit: The superb natural history illustrator Carl Buell

The diagram above shows a little Indohyus happy under the water, the animal had a long tail,  this was almost the length of its body.  The tail may have been flattened and broadened to help it to swim.

Lead researcher Hans Thewissen commented “what we think happened is that the ancestors of both Indohyus and whales were animals that looked like tiny deer”.  Discussing the apparent herbivorous habit of Indohyus he added “apparently the dietary shift to hunting animals, as modern whales do, came later than the habitat shift to the water”.

The research team, whose work has just been published in the journal Nature conclude that Indohyus was probably not a direct ancestor of modern cetaceans as the fossil remains of this little animal date 48 million years ago, whilst remains of marine mammals such as Pakicetus date from at least 50 million years ago.

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