Sagot :
Answer:
The evolution of whales
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 ancestors of both these groups were terrestrial.
These first whales, such as Pakicetus, were typical land animals. They had long skulls and large teeth that could be used for eating meat. From the outside, they don’t look much like whales at all. However, their skulls — particularly in the inner 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.
Explanation:
Early ancestors
Indohyus
A small deer like creature that lived about 48 million years ago and resembles a small deer, but was only about the size of a raccoon.
The sister group of the (pakicetidae) indohyus share several characteristics with cetaceans (whales) including an unusual characteristic only found between the two species known as an Involucrum (A layer of new bone growth outside of existing bone).
Pakicetidae
Pakicetids are hoofed mammals that lived around 53 million years ago and are considered the earliest form of whale acnestory with indohyus being the closest sister family.
Pakicetids fossils were first discovered in pakistan in 1979 and appear not to have been designed for swimming due to their legs and short hands and feet.
Pakicetids teeth are also similar in shape and design of the fossil whale.
They had unusually thick bones which seem to have been a way to make it easy to float on water rather than swim underneath the ocean.