232 KNOWLTON 



yet there seems good reason for believing that dinosaurs were con- 

 temporaneous with Puerco mammals." ... It is extremely 

 unsafe to say when and where these strange reptiles breathed their 

 last, for the presence of fossils is certain evidence of the existence of 

 life, but the lack of them is no evidence of its absence. Dinosaurs 

 may have continued long in the Eocene, but conditions in the places 

 where so many mammalian remains have been found may not have 

 been favorable for them. 



The causes which led to the extinction of the dinosaurs are of 

 course unknown and may always remain so. Being highly special- 

 ized and supposedly sensitive to environmental changes, it is difficult 

 to imagine what could have caused their sudden and absolute deci- 

 mation. An orogenic movement with the effect it would have had 

 on climate and vegetation; the draining of the waters in which, or 

 beside which, they lived; the sudden incursion of mammal enemies 

 able to cope with them; the outpouring of volcanic material; these, 

 or any one of them, might account for their disappearance, but we 

 have no evidence of the occurrence of either of these phenomena. 

 If there was a change in climate, it was not reflected in the flora; if 

 there were enemies, their remains have not been found; if there were 

 volcanic disturbances, the ejectamenta are not present in the sedi- 

 ments, and finally, the waters were not drained; for sedimentation 



*' A striking confirmation of this prediction has just been brought to the 

 writer's attention, this being an important discovery made by Mr. Jas. H. 

 Gardner, of the U. S. Geological Survey, during the field season of 1908. At 

 a point near the head of Coal Creek, i mile southeast of Ojo Alamo, New 

 Mexico (about 12 miles south of Farmington), in variegated sands, shales 

 and conglomerates, indisputable above the unconformity at the top of the 

 Laramie, and thus apparently of Puerco age, he found "near the top of the 

 section" vertebrate remains which have been studied by Mr. C. W. Gilmore 

 who reports the presence of Triceratops, Trachodon, Tyrranosaurus, Aspidi- 

 retes, and crocodiles. Of this fauna Mr. Gilmore says: "Appears to repre- 

 sent a typical fauna of the so-called Laramie, or better, Ceratops beds." 

 The significance of finding a typical "Ceratops beds" dinosaur fauna in beds 

 that are more than probably of Puerco age, is apparent. It is also of inter- 

 est to note that this locality (Head of Coal Creek) is exactly the same as that 

 given by Wortman (Bull. Am. Mus. Nat. Hist., vol. vii, 1895, p. 2) as one 

 of the localities at which he obtained Puerco mammals. And in this con- 

 nection it may be added that the writer has just been informed that dinosaurs 

 have been found associated with mammals in the so-called Pyrotherium beds 

 of South America, which, it is said, are of acknowledged Eocene age, and 

 correspond approximately to our Puerco. 



