i?ORSTL FOOTPRINTS OF TITF JFRA^TRIAS. 



471 



the claw is absent the ungal as well as the penultimate phalanx must lie entirely within 

 the distal pad as in digit 1 of Chirotherium barthi (pi. 72, fig. A) . 



Prehensile and locomotor terrninaJ claws. — In the less specialized dinosaurs, even 

 among the carnivorous forms, the anterior ungals of the pes do not seem to have borne 

 prehensile claws, though such were undoubtedly borne on those of the manus and in all 

 probability upon the hallux as well, as long as the latter remained functional. The 

 increase in curvature of the pedal ungals and the consequent development of the claws 

 seem to be correlated with the reduction of the manus as a prehensile organ, apparently 

 reachino- its highest expression in AUosaurus and the later Megalosaiaria. In Dimodo- 

 saurus, a Triassic Megalosaurian dinosaur, the ungal phalanges are less curved than in 

 AUosaurus and the facets indicate that while in the latter the ungal could be flexed 

 through an angle of fully 00°, in the former the possible movement was very slight, as 

 in the later Orthopoda. 



Digital reduction in relation to the tracks.— Sevi^vdl stages in the digital reduction in 

 the pes may be observed among dinosaurs, an understanding of wliich will aid in the 

 interpretation of the tracks. 



First, the Anchisaurus (a carnivorous Triassic dinosaur) stage. Here the hallux is 

 complete, insistent, that is, only the tip of the claw touches the ground, rotated backward 

 and probably highly efficient as a grasping claw. Digit V is represented by the proximal 

 half of the metatarsal, and the proximal end of metatarsal II is narrow on its anterior 

 face. This stage is represented by the track genus Anchisamipus. 



Second, the Compsognathus (a carnivorous form from the Jurassic of Bavaria) 

 stage. The hallux is complete, slender, insistent, and half rotated, functional though 

 possibly not to so high a degree as in the preceding stage. Digit V is represented by 

 the proximal end of the metatarsal only, and the anterior face of the upper end of meta^ 

 tarsal II is still narrow. This stage is represented among the footprints by Anomoepus, 

 the manus and pes of which are quite like those of Hypsilophodon, though in Anomoepus 

 the pes is much more elongate and slender. 



The third stage of digital reduction is that of AUosaurus (a carnivorous Jurassic 

 form) wherein the first metatarsal is not completely ossified in the shaft indicating a par- 

 tial loss of function on the part of the hallux. This digit is incumbent, that is, its whole 

 length rests on the ground, and it is little more than half rotated. Digit V seems to be 

 obsolete and the proximal anterior face of metatarsal II is the widest. This stage is 

 represented by Gigandipus among the tracks. 



Fourth, the Dryosam-us (an lierl)ivorous Jurassic dinosaur) stage in which the hallux 

 is represented by the proximal half of the metatarsal only, the claw being absent. Digit 

 V is also absent. The ichnite Eubrontes may belong to this stage, for the foot seems to 

 be structurally tridactyl, the imprint of the hallux never ha\ing been observed. 



