NO. 3 GRAND CANYON FOSSIL FOOTFRINTS — GILMORE 2/ 



AGOSTOPUS MEDIUS, new species 

 Plate 8 



Type. — Catalogfue number 11.509. U. S. N. M. Consists of a trail 

 870 mm. in length, showing consecutive impressions of all four feet. 



Type locality. — -Hermit Trail, Hermit Basin, Grand Canyon Na- 

 tional Park, Arizona. 



Geological occurrence. — Coconino sandstone (about 150 feet above 

 the base), Permian. 



Description. — Average length of stride about 170 mm., width of 

 trackway about 230 mm. Hindfoot: I.ength about 75 mm., hindfoot 

 placed in front of forefoot, the sole usually obliterating toes of the 

 manus. Sole wider than long, palmate, broadly rounded behind. Sole 

 longer than digits. Four, possibly five, toes, the two middle ones 

 sharply pointed and strongly curved outward. First and fourth short 

 and heavy, with bluntly rounded terminations apparently without 

 claw ; first often not impressing. Length of digits, 1 = 4 mm. ; 

 n = 23 mm. ; HI = 30 mm. ; IV = 16 mm. While the trackway as a 

 whole gives the impression of being clearly defined, when it comes to 

 considering the details of the foot plan the specimen leaves much to be 

 desired. On the type slab there are ten imprints made by the two hind- 

 feet, but only two of these in the lower left hand side (see pi. 8) show 

 the undoubted presence of a short, obtuse first digit. It is either miss- 

 ing entirely from the other tracks or else there is only the slightest 

 trace of its existence. Where the imprint is missing, the inward exten- 

 sion of the sole is always sufficient to have carried it. In a few of these 

 tracks on both sides a projecting protuberance on the outer posterior 

 angle of the sole (see fig. 11) may represent the presence of a fifth 

 digit, but additional specimens are necessary before this point can 

 be definitely decided. Forefoot: Length (estimated) about 40 mm., 

 width about yz mm. Sole suboval in outline. Smaller than pes. Nutn- 

 ber of digits uncertain, probably five, apparently reducing inward. 

 All short, stout, with broadly rounded terminations and apparently 

 without claws. Fifth set ofif from the others. The uncertainty re- 

 garding the digits of the manus is largely brought about by their 

 partial obliteration by the flow of sand crowded back upon them by 

 the impact of the heel of the hindfoot. 



A portion (negative) of this same trackway was collected in 1924 

 and presented to the Grand Canyon National Park Museum, while 

 the positive portion ( No. 1 1,136, U. S. N. M.) was brought to Wash- 

 ington under the impression that the tracks were duplicated in other 

 specimens in the collection. Critical study demonstrated its distinct- 



