Friday, 6 December 2013

The Origin of Whales and Dolphins

Whales and dolphins belong to a group of animals called cetaceans. All cetaceans live in water today but their ancestors were land animals. 

The closest relative to today’s cetaceans is the hippopotamus. Whale ancestors left the land about 50 million years ago and became the baleen whales (plankton feeding) and toothed whales (fish and squid eaters) of today.

Humpback Whales

What did the early whales look like and how did they live?

The first fossils were found in the United States and were so different from modern whales that they were described as a reptile (dinosaur). Because of their size, they were named Basilosaurus, or king lizard. Many fossils were found with an average length of 18 metres and scientists believed that they may have reached 45 metres. Fossils have been found in Pakistan and Egypt and may have given rise to early worship of crocodile-like gods.

They were so different from modern whales that they were described as a reptile (dinosaur).

But they weren’t lizards!

We now know that the fossil Basilosaurus was a whale that probably hunted in shallow seas between 34 and 40 million years ago. It was about 18 metres long and the biggest animal on Earth at that time.

It had small paddle like hind fins that were left over (vestigial) from what were once legs. They were so small that the Basilosaurus probably swam more like a snake than a modern whale.

We can be very certain (look at the teeth) that Basilosaurus was an aggressive and dangerous predator. Careful examination of the skeleton suggests that Basilosaurus may not have been a long distance swimmer and probably could not dive to great depths. Its head and teeth are reminiscent of a crocodile’s and it may have hunted in a similar way; surprise attacks in shallow water or swimming down unfortunate prey.

Another 30 million years of evolution finds us sharing the planet with 81 species of whales from the metre long Hector’s dolphin to the Blue Whale, the largest animal to have ever lived on Earth.

Blue Whale and its calf