The fossil record indicates the existence of a group of four-legged mammals living at the edge of an ancient sea, called Tethys, in what’s now India and Pakistan.
Scientists think these wolf-like creatures scavenged for food at the water’s edge, gradually venturing deeper into the sea to look for food. It’s believed that these creatures finally abandoned land completely and made the sea their home.
Fossils reveal a progression from four-legged seaside scavengers to amphibious seal-like creatures to fully aquatic predators with small hind legs. The back legs gradually disappeared. Nostrils in front of the head became blowholes above the head.
While these changes took place, the structure of their earbones retained similarities to their terrestrial cousins, part of the evidence that demonstrates the relationship. Ultimately, their bodies became streamlined, until the creatures became recognizable as the great whales we know today.
Of course, this extraordinary transformation took a long time – about 50 million years, according to the fossil record.
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