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Proselachii. : 16. Natidanides. Chlamydoselachius. Heptanchus. Silurian. 17. Ganoides. Plated-fishes. Proganoides. : 17. Accipenserides. Devonian. : 18. Dipneusta. Paladipneusta. : 18. Neodipneusta. Ceratodus. Protopterus. Carboniferous. : 19. Amphibia. Stegocephala. : 19. Phanerobranchia. Salamandrina. Permian. : 20. Reptilia. Proreptilia. : 20. Rhynchocephalia. Primitive lizards. Hatteria.
Hence Hatteria is the phylogenetically oldest of all living reptiles, an isolated survivor from the Permian period, closely resembling the common ancestor of the Amniotes. It must differ so little from this extinct form, our hypothetical Protamniote, that we put it next to the Proreptilia.
The embryos of the reptiles and birds are identical until a very late stage, and have an astonishing resemblance even later. Their whole structure agrees so much that no anatomist now questions the descent of the birds from the reptiles. On the other hand, the mammal line has descended from the group of the Sauromammalia, a different branch of the Proreptilia.
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