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.
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