Hyenadon

A long time ago, in north america, there was an animal called the Hyenodon, it was some mix of cat and dog.

These hyenas where much smaller than today hyenas and much more primitive. That was one of the reasons it got extinct, it was so primitive it did not survive the modern times.

It used to kill American Rhinos.

There was also the saber tooth cat, the hyenodon used to kill this cat and other animals biting it's head and breaking the skull.

It got extinct because it's prey got faster and left the hyenodon away from it's north american top predator crown in the hands of the Bear-Dog. The Bear Dog started geting hyenodons prey making all of them with no food, they died.

As they were extinct they became todays dogs and cats.