What structural features bring mammals closer to reptiles? Prove that first animals are closer to reptiles than other mammals.

The assumption that mammals are related to reptiles is based on the presence of a number of common structural features in them. These include a developed cornea, the presence of pelvic kidneys, internal fertilization, and the development of the embryo in a water sac filled with fluid.
The greatest similarity with reptiles is observed in animals of the most ancient group of mammals – primitive animals (platypus, echidna). In addition to the above general features of the structure with a reptile, they have some other essential common features. So, they reproduce by laying eggs, in their shoulder girdle, coracoids are developed as independent bones, there is a cloaca.