R. S. Lull — Dinosaurian Distribution. 3 



(Diplodocus) among sanropods occur in the same quarry and 

 were therefore contemporaneous. (Hatcher 1903, p. 57). 



Of the plant-feeding Orthopoda there are three main types, 

 which have differentiated from the original stock ; one, the 

 unarm ored Ornithopoda, paralleling the carnivores in general 

 bodily contour and bipedal gait, though bringing the fore 

 feet to the ground when occasion demanded. Like the car- 

 nivores they too included a greater and a lesser race. The 

 former, like Iguanodon of the Wealden of Europe and Camp- 

 tosmcrus of the American Morrison, culminated in Trachodon 

 of the late Cretaceous ; while the latter are represented by the 

 fleet Laosaurus of North America and Hypsilophodon of 

 Europe. 



On the other hand, two groups of armored, secondarily quad- 

 rupedal dinosaurs arose, possibly derived from the same branch 

 of the Orthopoda, possibly of independent origin. These 

 were the Stegosauria, the defensive sort with small head and 

 heavy body armor sometimes forming, over part of the body 

 at least, a veritable cuirass or carapace ; and the more aggressive 

 Ceratopsia with huge armored skull, but, so far as our knowl- 

 edge goes, bereft of any special body mail. The first are 

 represented by the British Polacanthus and the American 

 Stegosaurus, while the last have a splendid representation in 

 that most grotesque of dinosaurs, Triceratops from the Ameri- 

 can Laramie. 



Y. Huene (1907-1908, p. 351) derives the Sauropoda from 

 the early Theropod dinosaurs of the Trias, seeing in the genus 

 Plateosaurns the annectant type. In his scheme of relation- 

 ships (v. Huene 1909, p. 22), however, he seems to defer the 

 divergence of the Sauropoda from the Plateosauridse until the 

 Lias, which would hardly give time for the profound change 

 shown by either Cetiosaurus or Dystrophceus of the Dogger. 

 It is my impression that the divergence occurred earlier in 

 Triassic time. 



Of annectant forms, linking the Theropoda and Orthopoda, 

 none is suggested by v. Huene among known types, as our 

 known record of the latter does not go back far enough in 

 time. Of the Stegosauria, Scelidosaurus of the English Lias 

 seems to be the most primitive as it surely is the oldest ; it is, 

 however, still removed from the Ornithopoda and a common 

 ancestor must again be sought in more remote strata. 



The Ceratopsia may have their earliest representative in 

 Stenopelix of the Wealden of Briickeburg. Y. Huene (1907- 

 1908, p. 374) has shown strong points of resemblance between 

 the pelvis of Stenopelix and that of Triceratops. Whether, 

 as he suggests, one can derive the phylum from the Scelido- 

 sauridan stem, or whether the group represents an independ- 

 ent offshoot from the Orthopod stock, is not quite clear. 



