III.—Saurischia and Ornithischia

Extract

In 1888 the late Professor H. G. Seeley pointed out for the first time (Rep. Brit. Assoc. Adv. Sci., 1888, pp. 698–9) that Owens' order ‘Dinosauria’ should be divided into two great natural groups, especially on account of their pelvis. He called them Saurischia (=‘Theropoda’ + ‘Sauropoda’) and Ornithischia (=‘Orthopoda’). He maintained his, classification until his death in 1909, but nobody followed him. Only in 1907 did the present writer accept this classification and gave new evidences for it, but still was of opinion that these two groups only were ramifications of one natural unity, the ‘Dinosauria’. But now, for several years, the writer has come to the conclusion that the ‘Dinosauria’ are not of monophyletic origin, but have developed from different points, and should therefore be considered as two distinct natural orders. Superficial similarities have been valued too highly, such as general form and size of the body, bipedal locomotion in two large groups, certain similarities in the formation of the foot, the femur, the humerus, and the shouldergirdle.