2 AMERICAN MESOZOIC MAMMALIA 



The first reputed American Mesozoic mammal was Dromatherium, described by 

 Emmons in 1857. Although this form and a second genus, Microconodon, described 

 by Osborn, were for many years widely accepted as mammals, this status was several 

 times challenged and in a recent exhaustive study (1926E) the present writer has at- 

 tempted to show that both genera should be referred to the Reptilia and that true mam- 

 mals are as yet unknown in the American Triassic. It was not until the epoch of the 

 first extensive explorations for dinosaurs in the American West that the first true 

 Mesozoic mammals were found. 



Although some isolated specimens of dinosaurs had previously found their way to 

 the East, it was not until 1877 that the true discovery of our western dinosaur fields 

 was made. In that year abundant remains were found almost simultaneously at several 

 points in Colorado and Wyoming. One of these localities was Como Bluff in south- 

 western Wyoming, a locality to which the still unwritten story of early American 

 exploration for fossils will necessarily devote one of its most fascinating chapters. One 

 of the original discoverers soon passed from the scene, but the other, William H. Reed, 

 was, if not continuously present, never long absent. Most of the earlier work here was 

 done by him or under his direct guidance. Early in 1878 Reed discovered and sent to 

 Professor Marsh in New Haven a small broken jaw with a single tooth. This was at 

 once recognized as a Jurassic mammal and became in the same year the type of Dryo- 

 lestes friscus Marsh. The field workers were directed to bend all their energies to the 

 discovery of other jaws. It was in 1879 that the now famous Mammal Quarry, Quarry 

 9, was discovered. With the exception of the first specimen (from the surface at some 

 distance from Quarry 9), of one from Quarry 11, also at Como Bluff, and of three from 

 Canyon City in Colorado, all of the hundreds of mammals from the Morrison forma- 

 tion came from this one quarry. Although the dinosaur quarries, especially the almost 

 equally famous Quarry 13, were often worked instead or simultaneously, work con- 

 tinued in Quarry 9 for several years. 



The size of the collection thus made can be judged from the fact that at Yale alone 

 there are about two hundred and fifty separate specimens of jaws or teeth from Como 

 Bluff, mostly very fragmentary to be sure. Marsh published the most striking of this 

 material as it came to his hand (1878, 1879A, -b, -c, 1880, 1881). In 1887 he published 

 a regrettably brief general paper in which all the previously mentioned forms were re- 

 viewed and several new ones added, with woodcuts of at least one specimen of each 

 genus as then understood. At this time there were noticed 14 genera with 25 species, 

 and until 1925 no new ones were added to the list of Morrison mammals. 



The year 1888 was notable for the appearance of the second comprehensive mem- 

 oir on the Mesozoic Mammalia, that of Professor Henry Fairfield Osborn.^ This was, 

 until the present work, the only comprehensive study including the many forms dis- 

 covered between 1871 and 1887 and it contains the first attempt to place all these ani- 

 mals in a natural zoological classification. Based chiefly on a review of the British 

 Museum collections, it necessarily relied on the published data for the American 



'^ The first was that of Owen in 1871. 



