510 



(!EOLO(iY OF THE DENVER BASIN. 



abundant in these deposits, and characteristic of the horizon wherever it 

 hiis been found. The entire vertebrate fauna of these strata is of great 

 interest, and is only surpassed in this respect by that of the Atlantosanrus 

 beds above described. The dinosaurs are here still the dominant forms, 

 but arc more highly specialized than those of the Jurassic horizon. Other 

 reptiles were also abundant, including plesiosaurs, crocodiles, turtles, and 

 serpents, while amphibians and fishes were much more numerous. Ikmes 



i'ii, 71 skull ;iinl lowei 'jaw ..i' Pteranodon longiceps Marsh ; Bide view. 

 I'H. 72. The same skull; top view. 



I [Q. ! I l In iiim- skull ; bottom vit'U . 



in.. 7t I .nun- j:tu nf Pteranodon longiceps; top view. 



All tin- figures are >.eightn natural size. 



<i. antorbital aperture; &, orbit; c, sagittal crest; </, angle of jaw; e, Lower margin of upper jaw ; e\ uppei' margin 

 of lower jaw; /, articulation of lower ja*fl , "<\ oooipita] i <mi!\ le; <;, quadrate I ; .v. symphysis of lower jaw. 



of several birds have been found, while remains of small mammals of 

 primitive types are abundant in many localities. 



Tlie gigantic horned dinosaurs, as the most characteristic forms in 

 this horizon, will first claim attention, and the skull of one of the best- 

 known genera of the group is well shown in fig. 75. A front view of 

 the same skull is represented in fig. 76, and the posterior view of another 

 in fig. 77. A tooth of Triceratops is given in fig. 78, showing the double 

 roots, the only case among the Reptilia. Another interesting specimen, 



