NO. 3 



GRAND CANYON FOSSIL FOOTPRINTS GILMORE 



39 



and fourth toes usually in line across the palm of the foot, the former 

 pointing inward and backward, the latter outward and forward as 

 shown in figure i6. As in the pes the palmar impressions are hardly 

 more than a suggestion. Forefeet usually inside the line formed by 

 the hindfeet. 



Such differences as may be noted between the forefeet of this and 

 Lull's type may be more apparent than real for it must be remem- 

 bered that Lull had but a single impression of the manus ( see fig. i6) 

 in the type, and as we well know the same trackway often exhibits 

 differences in the toe plan in successive imprints made by the same 

 foot (see fig. 15). It is, therefore, important to have trackways of 

 some length in order to be sure of the precise arrangement of the 

 digits. 



Comparative Measurements 



Type 

 No. 2146 V.M. 



No. 11,519 

 U. S. N. M. 



Length of stride. . 

 Width of trackway 

 Length of manus. . 

 Width of manus . 



Length of pes 



Width of pes 



mm. 



57-0 

 45-0 

 7.0 

 10.0 

 10.5 

 13.0 



A second series of small five-toed tracks on this same slab (see B, 

 fig. 15) but crossing the trackway just described at right angles, is 

 of interest as showing the apparent capability of this animal to walk 

 entirely on the hind legs. This series, which may be clearly traced 

 for a length of 290 mm., gives nowhere any evidence of the front 

 feet. Furthermore the lengthened stride, 82 mm., and narrowed 

 trackway, 34 mm., give corroborative evidence in support of this 

 conclusion. In proportions of foot and relative arrangement of the 

 digits the impressions of the hindfeet in the two trails are essentially 

 identical and while both may not have been made by the same indi- 

 vidual, they were quite certainly made by the same kind of an animal. 

 That small, crawling quadrupedal animals often assume the bipedal 

 mode of progression for short distances has often been observed 

 among the small lizards of the southwestern United States, as has 

 been convincingly portrayed by Sayville Kent in excellent photo- 

 graphs. However, it is rather surprising to find an amphibian doing 

 likewise since our living amphibians are usually slow and sluggish of 

 movement. 



