FOSSIL FOOTPRINTS OF THF .TITRA-TRIAS. 469 



while the overlying hard sandstone several inches in thickness preserves upon its under 

 surface the footprints in high relief. This is paralleled in the Chirotherinni localities in 

 Hessburg, Saxony, and at Storeton f|narry, in England. 



Most of the footprint localities were well out in the ancient bay and were evidently 

 tidal flats which were daily left bare by the ebbing waters as the occasional record of a 

 shower of rain associated with the footprints gives evidence. The presence, at times, of 

 ripple marks and other littoral features lends weight to the tidal theory. 



Three factors aided in the preservation of these remarkable remains. First, the 

 fierce heat of a tropical sun, for the plant fossils are sufficient evidence of such climatic 

 conditions. Emerson ('98. p. 379) ■ says that all of the famous localities were out in the 

 ancient bay in sandstones that rest directly on the back of the bi'oad trap sheets and not 

 very high above them and that the heat which emanated from the not yet cooled lava 

 together with the iron which was liberated by its decomposition constitute two very effi- 

 cient agents, the second and the third, for the preservation of the impressions. 



Skeletal remahis. — With the exception of fishes, the actual vertebrate fossils are 

 extremely rare, but few localities having yielded tliem. Such as have been found are the 

 remains of dinosaurs and they seem to indicate that the great majority of the carcasses 

 which found their way into the water wei^e swept out to sea by the tide and irrevocably 

 lost, or that the conditions were not right for their preservation. The rarity of the 

 remains would argue in favor of terrestrial as opposed to either wholly or partially 

 aquatic habits on the part of these forms. 



Dbiosaurian characterfi in the tracks. — The assumption that the majority of the 

 vertebrate tracks are those of dinosaurs seems readily proven though the proof of the 

 non-existence of birds is rather more difficult than the elimination of other vertebrates. 

 The foot characters wherein the birds and the dinosaurs agree are : first, the digitigrade, 

 functionally tridactyl pes, though in both grcnips the foot is generally structurally 

 tetradactyl. The phalangeal formula, 1st digit, 2; 2d digit, 3 ; 3d digit, 4; 4tli digit, 5, 

 is identical in each group and the order of reduction of the chgits is the same, namely: 

 first, V, the outer digit, then I, the inner digit or hallux, and never first, 1, as in 

 mammals. Another common character is the length of limb as compared with the length 

 of the foot, a long legged form being indicated by a long stride and naiTow trackway. 

 Finally, the bipedal walk as opposed to the sprawling quadrupedal gait of the majority 

 of modern reptiles is nn annectant character. 



The features which separate the tracks under consideration from those of birds are 

 several, though all do not occur in each instance. They are : first, the presence of a 

 tail trace which is unquestionably reptilian. This may be a continuous serpentine impres- 

 sion or a series of short straight ones as though the appendage were raised at each step. 



