1877.] ^"^ [Cope. 



On the Vertebrata of the Dakota Epoch of Colorado. 



By E. D. Cope. 



(Bead before the American Philosophical Society, December 21, 1877.) 



Not long since I was informed by the Superintendent of Public Schools 

 of Fremont County, Colorado, Mr. O. W. Lucas, that he had discovered 

 the bones of an enormous saurian at an outcrop of the rocks of the Dakota 

 group not far from Canyon City. I encouraged him to proceed with the 

 exploration, and asked him to send some specimens which would explain 

 the character of his discovery. One of the first objects sent, is a fragment- 

 ary lower jaw of a carnivorous dinosaurian, which he found on the surface 

 of the ground. This fossil was found to belong to a species heretofore un- 

 known, which I referred to the genus Laelaps, under the name of Laelaps 

 trihedrodon.* The second sending included a number of vertebrae, which 

 apparently represent a much more gigantic animal, and I believe the largest 

 or most bulky animal capable of progression on land of which we have 

 any knowledge. This reptile I described in my paleontological bulletin 

 No. 26, under the name of Gamarasaurus supremus. Subsequent send- 

 ings included many of the more important bones of the skeleton, which 

 render it comparatively easy to determine the general character of this 

 monster. Later collections received from Mr. Lucas include the teeth of 

 two large species of a new genus which has been characterized under the 

 name of Gaulodon ; and the vertebrae of three genera new to science, 

 which I have named Tichosteus, and Symphyrophus. He also pro- 

 cured remains of two additional forms of gigantic size, fit rivals of the 

 Gamarasaurus, which I referred to the new genus Amphico&lias. A spe- 

 cies of tortoise was associated with these saurians, and appears to have been 

 abundant. It is the oldest species of the order yet obtained from Ameri- 

 can formations, and is not very different from existing forms. 



The above named genera are the only ones from the Dakota horizon of 

 this continent which have been defined, up to the present time. 



The species of Gamarasaurus and Amphicoilias, which attained to the 

 most gigantic proportions, are remarkable for the light construction of the 

 vertebrae anterior to the tail. In both genera the centra of the dorsal ver- 

 tebrae are hollow, including two large chambers which are separated by a 

 longitudinal median wall, and which communicate with the cavity of the 

 body by a foramen on each side. They are also remarkable for the enor- 

 mous elevation of the superior arches, and diapophyses, the result of which 

 is to give the ribs an unusually elevated basis, and the cavity of the body 

 much space above the vertebral axis on each side. On the other hand the 

 bones of the tail and limbs are solid or nearly so, in great contrast with 

 some of the Dinosauria of later geological periods. Another peculiarity of 

 the genus Gamarasaurus at least, is the probable great length of the an- 



* Bullet. U. S. Geol. Surv. Terrs. Ill, 1877, p. 805. 



PR0C. AMER. PHILOS. SOC. XVII. 100. 20. PRINTED JAN. 12, 1878. 



