F. R. von Hucne — Dinosaurs not a Natural Order. 145 



Art. XI. — The Dinosaurs not a Natural Order ; by F. R. 



von Httene. 



In 1888 the well-known British investigator, H. G. Seeley, 

 demonstrated* for the first time that Owen's order " Dinosauria" 

 should be divided into two large natural groups, especially on 

 account of pelvic differences. Seeley called these groups 

 Saurischia (= Theropoda + Sauropoda) and Ornithischia (= 

 Orthopoda). This classification he kept until he died in 1909, 

 but nobody followed him.f In 1907, the writer, however, 

 accepted Seeley's classification and gave new evidence for it, 

 but was still of the opinion that the two groups were only 

 ramifications of one natural unit, the Dinosauria. But several 

 years ago he came to the conclusion that the Dinosauria are 

 not of monophyletic origin, but have developed from two 

 different stocks and therefore should be considered as consist- 

 ing of two distinct natural orders. Superficial similarities have 

 been valued too highly, as for instance, the general form of the 

 body, bipedal locomotion in two large groups, certain similarities 

 in the formation of the foot, the femur, the humerus, and the 

 shoulder girdle. The name "Dinosauria" should be abandoned 

 absolutely, as have been such names as "Enalosauria." 



The most striking difference between the Saurischia and the 

 Ornithischia is in the pelvis, as is generally well known. 

 Even in the oldest known representatives of these two groups 

 there is no convergence in this respect at all. In the 

 Ornithischia the facial part of the skull is prolonged and 

 without preorbital openings, except in the most primitive 

 forms, which have here a small fenestra. The dentition has 

 become more numerous and more specialized, the anterior end 

 of the jaws is toothless (except in the primitive Hypsilophodon) 

 and in the lower jaw (in one group also in the upper jaw) a 

 new symphysial bone has been formed, the premaxilla is of 

 enormous size and its posterior extremity is intercalated 

 between maxilla and nasals, even reaching the lacrymale 

 or adlacrymale. The enormous size of the internal bony 

 nasal openings and the different formation of the rest of the 

 palate, the freedom of the quadrate, the supraorbital forming 

 part' of the roof of the skull (as shown by the writer in the 

 Stegosauria, the Trachodontidse and the Ceratopsia) and the 

 high processus coronoideus in the lower jaw : all of these 

 features in the skull of the Ornithischia are differences from 



* Kept. Brit. Assoc. Adv. Sci., 1888, pp. 698-699. 



f Baur in 1891 reached the same conclusion regarding the invalidity of 

 the order, but divided it into three groups : Iguanodontia, Cetiosauria and 

 Megalosauria. See American Naturalist, vol. xxv, pp. 434-454. 



