Which is the best way to combine the sentences above using signal words or phrases?

Both the bodies of bats and the bodies of birds are covered in fur as well as feathers.

One way the bodies of bats differ from the bodies of birds is they are covered in fur, not feathers.

The bodies of bats are covered in fur, also the bodies of birds are covered in feathers.

The bodies of bats on the other hand are covered in fur, and the bodies of birds are covered in feathers.