Primordial whales gave birth on land

47 million-year-old fossils of two whales were discovered in Pakistan in 2000. One of them, a pregnant female, revealed new information on how whales made the transition from land to sea.

In fact, it is the first discovery of a fetal skeleton of an extinct whale in the group known as Archaeoceti, and the find represents a new species dubbed Maiacetus inuus. (Maiacetus means “mother whale,” and Inuus was a Roman fertility god.) The fetus is positioned for head-first delivery, like land mammals but unlike modern whales, indicating that these whales still gave birth on land.

The archaeocetes are a paraphyletic group of primitive cetaceans that include the earliest, terrestrial ‘whales’. The group consists of six families: Pakicetidae, Ambulocetidae, Remingtonocetidae, Protocetidae, Basilosauridae and Dorudontidae, although some scientists include the latter two in one single family Basilosauridae. The graph [top] above shows how these families are related to each other. Credit: University of Bristol.

The whales’ big teeth, well-suited for catching and eating fish, suggest the animals made their livings in the sea, probably coming onto land only to rest, mate and give birth... Like other primitive archaeocetes, Maiacetus had four legs modified for foot-powered swimming, and although these whales could support their weight on their flipper-like limbs, they probably couldn’t travel far on land.