54 Two Neiv Species of Fossil Footmarks. 



was in an incipient state, or had not begun. The resemblance is 

 certainly rather striking between this sketch and that on fig. 1 : 

 and it leads to the suspicion that some of the tubercular impres- 

 sions of the track may have been made by the metacarpal bones. 

 Such I suppose to be the character of a, a, a, a, fig. 3 ; and 

 when these were fully ossified, it is easy to conceive that they 

 might have been anchylosed into the structure in fig. 1, A. 



Professor Agassiz stated a principle of comparative anatomy, in 

 conversation on this subject, which is highly important, viz. that 

 the structure of adult fossil animals, that lived as early as the new 

 red sandstone period, corresponds more nearly with the embry- 

 onic structure of existing animals than with their adult develop- 

 ment. Taking this principle in connection with the above draw- 

 ing of the embryo-frog's foot, we are led to the conclusion, that 

 the animal which made these huge footmarks was probably a Ba- 

 trachian. 



It may seem a strong objection to such a conclusion, that the 

 animal was a biped : for what an anomalous being would a biped 

 frog be, with feet twenty inches long ! And yet there is one ge- 

 nus of living biped Batrachians, including the Siren lacertina of 

 Linnseus ; and its feet have four toes in one species, and three in 

 another* True, these animals have an enormously long tail drag- 

 ging behind. Yet it is not improbable, that in the new red 

 sandstone period, their bodies may have been more like that of a 

 bird : and such must have been essentially their form in order to 

 have produced the row of tracks exhibited on fig. 1. That bi- 

 ped Saurian s existed in the new red sandstone period, we know 

 from the case of the Rhyncosaurus : and the Pterodactyl proba- 

 bly walked for the most part upon two legs. And it is quite as 

 easy to admit the existence of biped Batrachians as biped Sauri- 

 ans. There is also reason to suppose, that some of these animals 

 may have been somewhat intermediate in their characters, and 

 have exhibited, like the Rhyncosaurus and Pterodactyl, a struc- 

 ture now found only in several classes of animals. 



Genus Otozoum, (iirog, the giant Otus, and Zuov.) 



Foot tetradactylous, pachydactylous ; toes all directed forward: 

 the inner one shortest ; the second longer, and the third the long- 

 est ; the fourth but little shorter : all making distinct tubercle- 

 like phalangeal impressions, the inner toes most so. Phalangeal 

 impressions on mud, three by the inner toe, four by the second, 



Two bones of the metacarpus, 



and 



articulated to the phalanges of the two outer toes, make a distinct 

 impression. Cushion beneath the carpus arching downward, and 

 sloping upward posteriorly. Animal bipedal. 



* Cuvier, Regne Animal, Tome ii, p. 120. 



