Question

The presence of a large coracoid in the pectoral girdle and oviparous reproduction in egg-laying mammals indicates which evolutionary relationship?

Options

• Mammals evolved from reptiles

• Reptiles evolved from mammals

• Birds evolved from mammals

• Mammals and reptiles are unrelated

Answer 1

Egg-laying mammals retain reptilian traits including a large coracoid in the pectoral girdle, oviparous reproduction with large yolky eggs and a shell, and a cloaca. Combined with their mammalian features, these characteristics indicate that mammals evolved from reptilian ancestors. This evolutionary relationship is further supported by the fact that egg-laying mammals represent the most primitive living mammals.