468 RICHARD SWANN LULL OX 



iiiithor has sought earnestly for avian incUcations. The class Mammalia seems also to be 

 unrepresented. 



Among the reptile tracks the majority seem to be dinosaurian in origin and are 

 referable to both the Theropoda, or carnivorous dinosaurs, and the Orthopoda, or her- 

 bivorous forms ; the great Sauropoda, herbivorous quadrupedal forms of the Jurassic, either 

 not having appeared or having been so truly aquatic and of such vast Imlk that they 

 could not wander over the shallow water flats and beaches where the ti-acks were formed. 

 Certain quadrupedal tracks show strong Theropod affinities and were doubtless formed 

 either by primitive dinosaurs or by the Diaptosaurian progenitors of that group which 

 survived side by side with the more specialized forms. Again, certain of the footmarks 

 show lizard-like characters, though no lizards are known from so remote a time ; others 

 are Chelonoid while yet others seem to be related to, or at least to resemble, early croco- 

 diles. 



Many of the tracks are beautifully preserved, showing even the most delicate tegu- 

 mentary impressions and it is upon these that the autlior has spent the larger part of his 

 time in the endeavor to learn the structure of the foot. Other of the remains are in 

 some instances extremely obscure and give little or no insight into their maker's form, 

 but in the revision of the fauna it became necessary to treat them as fully as conditions 

 would permit, but with very unsatisfactory results. 



Geological age and conditions. — The geological age of the beds in wliich the iclmites 

 are found is generally conceded to be upper Triassic, equivalent to the Keuper and 

 Khaetic of Europe, a correlation which is based upon the remains of fos.sil plants and of 

 fishes which they contain. From the evidence of the footprints themselves it is apparent 

 that the dinosaurs liad already reached a high degree of adaptive radiation and specializa- 

 tion, which would argue against the reference of the formations to any earlier period. 



The remains are found in at least two of the ten Triassic areas as enumerated by 

 Dana ('95, p. 741) and of these the classic locality is the valley of the Connecticut river in 

 a belt ranging from the village of Northfield, Massachusetts, to New Haven bay, a dis- 

 tance of one hundred and ten miles, and with a width of about twenty miles. 



The New Jersey localities are in the Palisade belt which extends from the Hudson 

 river, through New Jersey, Maryland, and Pennsylvania, to Virginia. 



The Connecticut valley belt is clearly of estuarine formation with the tidal ebb and 

 flow of water. It was also subject, locally at least, to conditions of flood which brouo-ht 

 down coarser debris from the surrounding country, as the sudden change in the character 

 of certain strata from shale to coarse sandstone gives evidence. An instance of this 

 occurs in the Otozoum beds of South Hadley, Massachusetts, where the layers upon which 

 the animals Avalked were so soft and fine in texture as to be incapable of preservation 



