[Geology2] The Evolution of Whales: How Did Whales Evolve?

The Evolution of Whales: How Did Whales Evolve?

What springs to mind when you think of a whale? Blubber, blowholes and
flukes are among the hallmarks of the roughly 80 species of cetaceans
(whales, dolphins and porpoises) alive today. But, because they are
mammals, we know that they must have evolved from land-dwelling
ancestors.

About 375 million years ago, the first tetrapods -- vertebrates with
arms
and legs -- pushed themselves out of the swamps and began to live on
land. This
major evolutionary transition set the stage for all subsequent groups of
land-dwelling vertebrates, including a diverse lineage called synapsids,
which originated about 306 million years ago. Though these creatures,
such as
Dimetrodon, looked like reptiles, they were actually the archaic
precursors
of mammals.

By the time the first mammals evolved 200 million years ago, however,
dinosaurs were the dominant vertebrates. Mammals diversified in the
shadow of the great archosaurs, and they remained fairly small and
secretive until the non-avian dinosaurs were wiped out by a mass
extinction 65 million years ago. This global catastrophe cleared the way
for a major radiation of mammals. It was only about 10 million years
after this extinction -- and more than 250 million years since the
earliest tetrapods crawled out onto land -- that the first whales
evolved. These earliest cetaceans were not like the whales we know
today, and only recently have paleontologists been able to
recognize them.

Read more:
http://ow.ly/3ldi7

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