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Updated: May 9, 2025
The extinct Protamniote, the ancestor of the whole group, belongs in its whole organisation to the reptile class. The genealogical tree of the amniote group is clearly indicated in its chief lines by their paleontology, comparative anatomy, and ontogeny. The group succeeding the Protamniote divided into two branches. The branch that will claim our whole interest is the class of the Mammals.
One of the most salient characteristics of the Amniotes is the complete loss of the gills. The Protamniote itself must have entirely abandoned water-breathing. But we do not find in the embryos of the Amniotes any trace of gill-leaves, or of real respiratory organs on the gill-arches. It is very probable that the urinary bladder of the Dipneusts is the first structure of the allantois.
Man is, in every feature of his organisation and embryonic development, a true Amniote, and has descended from the Protamniote with all the other Amniotes. The birds and mammals made their first appearance during this period. Even the reptiles show their greatest growth at this time, so that it is called "the reptile age."
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.
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