408 w. d. mattheav progress ix vertebrate paleontology 



The Dixosaues xot a xatural Order 



The dinosaurs are now generally recognized as not a natural order of 

 rejDtiles, but a composite grouj), including two distinct and rather dis- 

 tantly related orders.^^ Dinosaurs correspond in a way to pachyderms 

 among mammals, once considered a natural order, but now recognized 

 as an assemblage of animals superficially alike, owing to parallel adapta- 

 tion, but not really related. It is in this sense that the term "dinosaurs" 

 should henceforth be used and not as a natural order of reptiles. The 

 two orders are the Saurischia, including Marsh's two grou^DS of Sauropoda 

 and Theropoda, and the Ornithischia, or Orthopoda, the Predentata of 

 Marsh. The first group includes the gigantic amphibious Dinosaurs, the 

 great carnivorous Dinosaurs and their slender, swift-running allies, and 

 the more primitive Triassic dinosaurs. Orthopoda include the Iguano- 

 donts and duck-billed Dinosaurs, the horned Dinosaurs, and the armored 

 Dinosaurs. All these are distinguished by a horny beak or bill and a 

 more bird-like arrangement of the pelvic bones, and have a certain degree 

 of affinity to primitive birds, whereas the Saurischian order has a corre- 

 sponding relation to primitive crocodiles. The fine memoirs by von 

 Huene on various Triassic reptilia,^^ by Gilmore^^ on the carnivorous and 

 armored dinosaurs, by Osborn on C amarasaurus ,-^ and a series of de- 

 scriptive papers by Brown, Lambe, Parks, and others are the most impor- 

 tant published contributions in this field. 



Cexozoic Mammals of westerx America 



In the field of Tertiary mammals progress has been made at many 

 points. The great series of Tertiary faunas in this country has been im- 

 proved all along the line. Collections from each horizon have been 

 greatly increased ; many new or little known species are now represented 

 by complete skulls and skeletons. Careful intensive stratigraphic work 

 in the fossil fields and more exact records of all specimens enable us to 

 define more accuratelv the limits and succession of faunas and evolution 



^' F. Von Huene: (1909.) Skizze zu einer Systematik und Stammesgeschichte der 

 Dinosauiier, Centralbl. f. Min. Geol. u. Pal., J'g., 1909, s. 12-22 ; 1914. Natiirliche Sys- 

 tem der Saurischia, idem, 1914, s. 1.54-158 ; 1914, L^eber die Zweistlimmigkeit der Dino- 

 saurier u. s. w., Neues .Jahrb., B. B. xxxvii, s. 577-589. 



^^ Von Huene: (1912-1916.) Series of memoirs and shorter articles chiefly in Palaeon- 

 tographica : 1910-1914, Geol. u. Pal. Abhandl. ; 1920-1922. Acta Zoologica : 1909-1922, 

 Neues Jahrbuch and Centralbl. f. Min. Geol. u. Pal., etc. 



^" See page S, footnote 12. 



2" H. F. Osborn and C. C. Mook : (1921.) Camarasaiinis, Amjihiecplias and other 

 Sauropods of Cope. Mem. Amer. Mus. Nat. Hist., n. s.. vol. iii, pp. 247-887. pis. Ix-lxxxv. 



