474 RICHARD SWANN LULL ON 



suggests the probability of the evolution of wings, in some forms at least, first as an aid 

 to more rapid running, then to support the creature during long soaring leaps, and finally 

 for true fiight. It seems necessary to leave the question in this way until further evi- 

 dence as to the true nature of Gi'allator is found. 



Footprints and taxonomy. — It becomes at once clear to the student of ichnology that 

 while the various footprint species may represent definite stages in the evolution of the 

 foot, the number of definable genera and species must actually be far less than that of the 

 animals which made them. Marsh ('93) shows an appreciation of this when he says, in 

 speaking of the genera Anchisaurus and Ammosaurus: "So far as at present known the 

 footprints of the two reptiles would be very similar differing mainly in size." (Compare 

 figs. 4, 7.) 



(a) Variations in the inqvessions left by the same anhnal. There are, doubtless, 

 many instances of individual variation among dinosaurs of the same species other than 

 those of age and sex, and in the tracks, additional causes of variation come in, such as 

 the posture or gait of the animal or the character of the surface over which it w^alked. 

 The first of these factors has a notable illustration in the slab no. ^, of the Hitchcock 

 museum. On tliis specimen are impressed among others, two tracks, the one called by 

 Hitchcock the type of Anomoepus major, the other that of Fulicopus lyellianus, which 

 though referred to different genera, are in all probability the impressions of the same 

 individual ! In each case the size, form, and proportions are the same even to peculiar 

 markings, due to injury or some unusual cause, upon the sole of the foot. The differ- 

 ence is mainly in the hinder part of the track due to the fact that in one case the animal 

 was seated upon its heels, raising the posterior part of the foot a little off the ground, 

 while in the other the entire weight of the creature resting on the foot broadened it out 

 especially beneath the metatarsals and brought another pad into the impression (figs. 26, 

 27). 



[b] Inffiiencr of the coniposition and condition of the ground. The texture of the 

 ground upon which the animal trod, the fineness or coarseness of the sediment and the 

 degree of dryness are important factors. This is beautifully illustrated by the type speci- 

 men of AnontoepKs mrvatus, no. ff of the Hitchcock museum, of which a photograph 

 may be seen in Hitchcock ('65, pi. 15, fig. 2) . The slab contains five tracks of one animal 

 walking down the beach toward the water, two of the tracks being above the high w^ater 

 mark of the previous tide and three below. That portion of the shore above the mark 

 was drier and the tracks while well formed do not show the pad outlines and other mark- 

 ings as well as do the third and fourth where the surface was smoother and more moist. 

 Finally the fifth track is much deeper and owing to an uneven surface the hinder part of 

 the foot (lid not impress, altering the entire aspect of the footprint. 



