Further from my last post I mentioned a fossil whale most of you may never have heard of until this morning. Maiacetus inuus
"Inuus' Mother Whale", named for the Roman god of fecundity, and important features of the holotype, which I will come to.
The whale comes from Pakistan, known for some time now as an important place for whale evolution, the earliest whales (placed in a family called the Protcetidae) are known from here- previous finds include Ambulocetus natans
the "Swimming walking whale", Pakicetus
, originally known only from a skull, and now known to be a rather wolf-like animal, (rather than the seal-like creature it was previously reconstructed as), in total 15 genera and 16 species are known ranging from South Asia and Africa into North America.
Unlike later archaeocetes like Basilosaurus
and its relatives had strong back legs fused to the vertebral column. While strongly adapted to water they would have been able to move around on land, probably quite comfortably. Looking at the skeletal reconstructions I'm most strongly reminded of a cross between an otter and a crocodile. The limbs are strong, the snout long and narrow. The tail and limbs are strong, indicating that the animal probably swam rather like a modern otter. A 2.6m otter with a face full of teeth. Not as cute as the ones at the zoo then.
The animal shows some degree of sexual dimorphism. The second specimen is 12% bigger than the other, and has notably larger canine teeth. This specimen is also one of the most complete protocetes known, and clearly shows the "double-pulley" ankle that shows whales are actually artiodactyls (the "Even-Hoofed Ungulates", like cows, pigs and sheep). Molecular data shows their closest living relatives are the hippos.
But I've been skirting round the main reason why this species is so fascinating, and why the bloggers have been picking up on it- The holotype is a pregnant
female. This is important for several reasons- its the first time a fossil whale has been found with a preserved fetus, and more importantly the fetus is lying head first in the birth canal.
We know that this is indeed a fetus and not the remains of her last meal because as the Phil Gingerich points out:
"Protocetids had shearing molars used to slice and chew their prey. The skull of the fetal skeleton could not have survived such mastication and be as well preserved as it is.
Because of their strong hind legs protocetes have been suggested as having given birth on land, but this fossil conclusively proves it. If Maiacetus
had tried to give birth underwater junior would have drowned immediately. Later whales like Dorudon
had to give birth to their young tail-first. Their legs are tiny and could never support their weight on land.
Another "missing link" found.
And if this wasn't awesome enough Gingerich PD, et al. (2009) New Protocetid Whale from the Middle Eocene of Pakistan: Birth on Land, Precocial Development, and Sexual Dimorphism. PLoS ONE 4(2): e4366 is freely available online at PLoS OneETA:
New Scientist has a nice gallery
showing the various stages of whale evolution, including Pakicetus