Name the two pieces of evidence that whales evolved from land mammals?
Answers
The first thing to notice on this evogram is that hippos are the closest living relatives of whales, but they are not the ancestors of whales. In fact, none of the individual animals on the evogram is the direct ancestor of any other, as far as we know. That's why each of them gets its own branch on the family tree.
Hippos are large and aquatic, like whales, but the two groups evolved those features separately from each other. We know this because the ancient relatives of hippos called anthracotheres (not shown here) were not large or aquatic. Nor were the ancient relatives of whales that you see pictured on this tree — such as Pakicetus. Hippos likely evolved from a group of anthracotheres about 15 million years ago, the first whales evolved over 50 million years ago, and the ancestor of both these groups was terrestrial.
These first whales, such as Pakicetus, were typical land animals. They had long skulls and large carnivorous teeth. From the outside, they don't look much like whales at all. However, their skulls — particularly in the ear region, which is surrounded by a bony wall — strongly resemble those of living whales and are unlike those of any other mammal. Often, seemingly minor features provide critical evidence to link animals that are highly specialized for their lifestyles (such as whales) with their less extreme-looking relatives.