0. C. Marsh — Footprints of Jurassic Dinosaurs. 227 



Aet. XXIII. — Footprints of Jurassic Dinosaurs ; by O. C. 

 Maesh. (With Plate Y.) 



One of the most interesting geological discoveries during the 

 past season in the Black Hills region was a locality of foot- 

 prints evidently made by Dinosaurian reptiles in deposits of 

 Jurassic age. These footprints are the first found in Jurassic 

 strata in this country. They are all tridactyle, of large size, 

 and were evidently made by some of the great Dinosaurs 

 known to have lived during Jurassic time. 



The tridactyle footprints hitherto found in this country were 

 nearly all discovered in the Triassic sandstone of the Connecti- 

 cut Yalley, and, as well known, were at first supposed to have 

 been made by Birds. They have since been discovered in 

 essentially the same horizon in New Jersey and also in 'New 

 Mexico. In the same strata, many other footprints have been 

 found, and among them numerous similar tridactyle impres- 

 sions, some of which may possibly have been made by birds, 

 but by far the greater number are evidently of reptilian origin. 

 It is an interesting fact that the bones of Dinosaurs found in 

 this horizon of the Triassic all pertain to animals of moderate 

 size, and none are known large enough to have made any of 

 the gigantic footprints so abundant in the Connecticut Yalley. 



In the Jurassic formation of this country, on the contrary, 

 the osseous remains of Dinosaurs of large size are especially 

 abundant, and among these were not' a few bipedal forms that 

 must have made footprints very similar to the so-called 

 bird tracks of the Triassic, but no footprints of any kind 

 have hitherto been found, although diligently sought for in 

 many localities. The present discovery fortunately supplies 

 the much-desired information on this point, and the specimens 

 already secured promise to throw much light on the life-history 

 of this interesting group of reptiles that were the dominant 

 forms of life during Jurassic time. 



When these footprints were first discovered, it was naturally 

 supposed they were of Triassic age, as all footprints of similar 

 character known in this country had been found in deposits of 

 that formation. The great development of red Triassic beds 

 in the same region, and their extension in a broad belt around 

 the Black Hills, where they are generally known as the " red 

 beds," all seemed to favor such a supposition. The character of 

 these beds of red shale and sandstone, all evidently deposited 

 in shallow water, as shown by the ripple marks and other well- 

 known features, indicated that footprints and other impressions 

 would certainly be found in them if proper search were made, 

 and this will doubtless prove to be the case. 



