What is the primary characteristic of a diagnostic structure that makes it useful for proving evolutionary relatedness?

It is present in a wide variety of unrelated species across different continents.

It is a unique trait that appeared in a common ancestor and was inherited only by its descendants.

It is a simple trait, like having four limbs, that is found in a large number of animal groups.

It appears in different species as a result of similar environmental pressures, not shared ancestry.

A paleontologist discovers a fossilized jawbone with a tooth shape never seen before except in a specific group of extinct rodents. What is the most likely conclusion the paleontologist can draw?

The fossil belongs to the known group of rodents.

The animal ate the same food as the rodents.

All animals with that tooth shape went extinct at the same time.

The fossil is from an animal that is older than the rodent group.

Feathers, which are also found on other birds.

A hollow bone structure, common to most flying birds.

A unique, interlocking joint in the wing that is not found in any other known bird species.

The ability to fly, which has evolved independently in other animal groups like bats and insects.

Because the backbone is an internal structure.

Because not all cows have a backbone.

Because the backbone is a trait shared by a vast group of animals (vertebrates), not unique to the cow's specific family.

Because the backbone's shape has changed too much over time to be useful for identification.

Suggest a possible, but unconfirmed, relationship.

Diagnose the diseases the ancient animal may have had.

Show that the animal was a predator.

Provide definitive proof of membership in a specific evolutionary group.