What characteristics is common in all vertebrates?

There are many such features, including:

1. Mammals nourish their young with milk.

2. Mammals are warm-blooded.

3. Mammals have fur.

4. Mammals have a four-chambered heart.

5. Mammals are amniotes.

6. Mammals breathe oxygen.

7. Mammals have three middle ear bones and a neocortex.

8. Mammals have internal reproduction.

Some of these characteristics are unique to mammals; others are found in some other vertebrates but not in all other vertebrates.