424 E. S. Riggs — Dinosaur Footprints from Arizona. 



therefore be inferred that the tracks were made by a bipedal 

 animal walking leisurely along a sandy beach. 



In outline the tracks are almost symmetrical to a line passed 

 through the imprint of the middle digit. The axis of the foot 

 is deflected but little from the line of stride. The middle digit 

 was evidently strongest and bore more than an equal share of 

 the animal's weight. The two lateral digits appear to have 

 been equally functional and, like the middle one, were armed 

 with claws. The inferior surface of the foot was provided with 

 pads similar to those of struthious birds. In digit II the weight 

 was borne upon the first and second phalanges, in digit III 

 upon the second and third, while in digit IV the second, third 

 and fourth were evidently brought to the ground. In addi- 

 tion to this there is an imprint of a heel-like pad which was 

 borne by the distal ends of the metatarsals. 

 Measurements are as follows : 



M 



Length over all _. '128 



Breadth. __ _ -103 



Length of lateral digits from heel *079 



Angle between digits II and III 35° 



« HI " IV 30° 



