A brand-new whale fossil

February 5, 2009 • 2:22 pm

Phil Gingerich and his colleagues at the University of Michigan, the Geological Survey of Pakistan, and the University of Bonn have just described a brand new and intriguing pair of whale fossils in the journal PLoS ONE, which you can find here. Tis whale Maiacetus inuus, lived about 47.5 million years ago, which puts it roughly at the time of the fossil whale ancestor Rodhocetus (see pp. 50-51 of WEIT). Rodhocetus was probably an amphibious creature, living on both sea and land, and this is almost certainly true of the new find as well.
The really intriguing thing about Maiacetus is that the female fossil contained an embryonic individual, apparently near term. This is the first known example of a fossil embryonic whale. What’s more, the embryo was positioned with its head facing the rear, so that it would be born head first. That birth position is characteristic of land-dwelling animals (probably an evolutionary feature to allow the embryo to start breathing as soon as possible), but is not found in marine mammals. In the latter group, babies are born tail first, probably so that a.) they won’t drown during birth and b.) so that they are born in the right position to immediately bond with and start following their mother.

There are other interesting features of this whale, too, like the permanent first molar teeth in the fetus, indicating precocial development
From the structure of its limbs and body, Maiacetus obviously lived on both sea and land, since the hind limbs are still substantial but reduced. The position of the fetal whale shows that it did, however, give birth on the land. Just another link in the ever-growing chain of fossils documenting the evolution of whales.

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