Samuel Wendell Williston

“ The earliest amphibians doubtless all had a single occipital condyle, an inheritance from their ancestral fishes—all that we know from the Lower Carboniferous had—of which only one known descendant with that character survived to the Permian. The reptiles, however, retained the single condyle until the beginning of their evolution into mammals, when they too developed a double condyle. ”

“ And thus, while we do not know from these later rocks, and probably never shall from rocks later than the Lower Carboniferous, all of the characters common to the two classes in any one animal, from the comparison of all it is not difficult to decide what were the primitive characters of the reptilian skeleton in almost every detail. ”

“ Characters that are common to many amphibians became more and more rare among the reptiles, and the amphibians, handicapped by inherited habits, were restricted more and more to subordinate rôles, and only a few of the more progressive continued to develop. ”