Question

1. which derived characters do mammals share with crocodiles?
2. which derived character makes mammals unique?
3. which derived character do crocodiles, birds, and snakes share?

Explanation:

Step1: Analyze shared traits of mammals and crocodiles

Mammals and crocodiles both have additional skull openings. They also both have amniotic eggs and four - limbs.

Step2: Identify unique trait of mammals

Fur is a unique derived character of mammals among the given options.

Step3: Analyze shared traits of crocodiles, birds and snakes

Crocodiles, birds and snakes all have amniotic eggs and additional skull openings. Snakes have lost their four - limbs in evolution, and fur is not present in them.

Answer:

1. four limbs, amniotic eggs, additional skull openings
2. fur
3. amniotic eggs, additional skull openings