This week's edition of Nature has a paper describing an extremely significant fossil, Indohyus : a small animal that has been shown to be a transitional form between terrestrial ungulates and marine mammals. Snip from the Science Centric article:Dr Thewissen and colleagues discovered of the skeleton of Indohyus, an approximately 48-million-year-old even-toed ungulate from the Kashmir region of India, as the closest known fossil relative of whales. Dr Thewissen’s team studied a layer of mudstone with hundreds of bones of Indohyus, a fox-sized mammal that looked something like a miniature deer. In work published in the current issue of Nature, Dr Thewissen and colleagues report key similarities between whales and Indohyus in the skull and ear that show their close family relationship.
The researchers used key morphological traits from the skull and ear to demonstrate the relationship between Indohyus and cetaceans. From the Nature paper's abstract:
The raoellid Indohyus is similar to whales, and unlike other artiodactyls, in the structure of its ears and premolars, in the density of its limb bones and in the stable-oxygen-isotope composition of its teeth.
Previously Ambulocetus (also described by Thewissen, in 1996), was the most definitive example of a transition between terrestrial and marine mammals, but the new animal is thought to have been even farther along the evolutionary path that resulted in whales and dolphins. Of course, any time you fill in one gap you create two more as far as the fossil record is concerned, so I doubt that anyone who previously objected to terrestrial ancestors of whales will be convinced by this discovery. For science, however, it is definitely a significant and fascinating find. The paper also discusses the dietary habits that could have contributed to the movement from land to shore to ocean, an example of how fossil remains can give us insights into the ecology of extinct species.
Thewissen, J. G., L. N. Cooper, M. T. Clementz, Sunil Bajpai, and B. N. Tiwari. Whales originated from aquatic artiodactyls in the Eocene epoch of India. Nature 450: 1190-1194.
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4 comments:
Damn you all! Am I the only one around the paleoblogosphere who does NOT have access to Nature and Science?
*raises fists to the sky*
Curse you, Last Frontier!!!
No worries, Mr. Miller, check your e-mail. :)
Ah, like the primate that I am I'll engage in some nit-picking: Indohyus is not on the main-line of cetacean evolution so in that sense it's not really transitional to whales (and it's actually younger than some of the early whales). Nor is it really "further" up or down the line of cetacean ancestry than Pakicetus or Ambulocetus.
If Thewissen and co are correct however, this darling little rat-deer-racoon-badger-whatever may give us a better idea of where cetaceans fit among the artiodactyls. And if Raoellids were in fact partially aquatic that's intriguing, though it doesn't necessarily tell us anything about the aquatic transition in whales.
At any rate a fairly complete Raoellid fossil is pretty exciting in its own right, whales aside.
Good points, Neil! It's amazing how ubiquitous the "ladder" image is, even though I *know* the "high vs low" animals paradigm is bunk it still unconsciously slips into language so much...
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