R. S. Lull — Footprints of Stegomus Longijpes. 381 



Aiit. XXXY. — Note on the probable Footprints of Stegomus 

 Longipes / by R. S. Lull. 



The discovery of a nearly complete specimen of Stegomus 

 in the Triassic sandstones of the Connecticut Valley proves a 

 great boon to the student of footprints, for it at once affords a 

 clue to the interpretation of a most remarkable series of quad- 

 rupedal tracks which are included under the ichnite genus 

 Eatrachopus (Anisopus) of Hitchcock. 



Briefly characterized, these tracks were made by a series of 

 forms truly quadrupedal in gait, with a tetradactyl pes and a 

 pentedactyl manus, the latter being considerably smaller and 

 rarely showing the impression of all of the digits ; sometimes 

 four, generally but three leaving their imprints. The phalan- 

 geal pads are generally distinct and betray a formula which at 

 once places the group among the diaptosaurian reptiles, while 

 the acuminate claws seem to imply a carnivorous mode of life. 



In one feature this genus separates itself 

 sharply from most Reptilia, and that is in 

 the extremely long stride in proportion to 

 the length of the pes, the ratio of foot to 

 step being on the average as one to six ; 

 this together with a very narrow trackway, 

 shown by the footprints being nearly in a 

 right line, would indicate a creature with 

 long stilted limbs and a gait like that of 

 a cursorial mammal. Edward Hitchcock 

 (Ichnology of Massachusetts, Boston, 1858, Footprints of Batracho- 

 pp 62, 63) recognized the saurian nature *£* "»***, H »£ 

 of the group, but could not reconcile the a manus, B pes. 

 limb proportions with those of any known 

 reptile, hence he reasoned that they might have been mammifer- 

 ous. The inequality of the fore and hind feet together with the 

 remote age of the impressions suggested to him the marsupials, 

 and he says finally that : u although the marsupial type must 



have predominated the .... crocodilian characters 



ought not to be overlooked, and therefore I call the animal a 

 Loriooid Marsupialoid." 



Lull, in his recent memoir (Mem. Boston Soc. Nat. Hist, vol. 

 5, No. 11, p. 482), thought that Batrachopus might represent a 

 survivor of the ancient dinosaurian stem from the very dino- 

 sauroid pes, which, though tetradactyl, with all of the digits 

 pointing forward, is of such a character that the typical dino- 

 saurian foot could readily have been derived from it The long- 

 limbed Kadaliosaurus strongly suggested the genus under con- 



Am. Jour. Sci— Fourth Series, Yol. XVII, No. 101.— Mat, 1904. 

 26 



