NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 



I2S 



been published. We now know the skull, practically all of the vertebral 

 column, the interclavicle, clavicles, coracoid, humerus, femora, and some of 

 the metapodial bones. For a long time after it was discovered no bones of 

 the limbs, feet, or pelvic and pectoral girdles were found associated with the 

 skulls and vertebra, and the animal was considered to be limbless. WilHston 

 first discovered and described the limbs and the coracoid. The broad skull, 

 terminating behind in the heavy horns of soHd bone, and the large plate-Hke 

 clavicles and interclavicle, show that the normal position of the animal was 

 flat upon the belly. The limbs were short and relatively weak; the posterior 

 a httle larger than the anterior; the body slender, terminating in a long tail. 

 It is possible that Diplocaulus may have been able to move with consider- 

 able rapidity through the water, driven by its strong tail. Broili suggests 

 that the presence of zygosphene and zygantrum articulations between the 

 vertebrae indicates some rapidity of motion. The weight of the abstirdly 

 large head at the extremity of the slender body suggests considerable mechan- 

 ical difficulty in the act of swimming. The head would have constantly 



Pig. 13. — Restoration of Diplocaulus magnicornis Cope and Lysorophus tricarinatus Cope. 



dragged downward, compelling a sustained effort of considerable power to 

 maintain a uniform lateral or upward motion. The broad, fiat head might 

 have acted as a guiding-plane to the animal's motion and, as long as held 

 horizontal or pointed upward, would maintain the animal's direction, but 

 the weight would soon drag it down, for there were no muscles or ligaments 

 adequate to support it, as is shown by the lack of an enlarged neural spine 

 upon the axis. It is to be noted, however, that the articular condyles lie 

 almost equally distant between the two extremities of the skull and the skull 

 may have been so balanced upon them as to give some freedom of movement. 

 It is far more probable that Diplocaulus habitually lay upon the bottom 

 of pools or streams, advancing by a wriggling motion, somewhat in the 

 fashion of Necturus, aided by the weak feet, or driven by strokes of the power- 

 ful tail. The location of the eyes and nostrils, entirely upon the upper surface 

 of the skull, is just such as would be most useful to an animal with such a 

 habit. Moving sluggishly over the slime of the bottom, it would devour 



