132 PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



paleontologists because of the long period of uncertainty as to its highly unique 

 structure and adaptations and its great rarity as a fossil, the latter due prob- 

 ably to its forest-frequenting habits. 



With its companions, the giant elothere pig, known as Dinohyus, and the 

 diminutive pair-horned rhinoceros, Dicer atlierium, its remains have since 1882 

 been found in profusion in the Agate Spring Quarry of Sioux County, western 

 Nebraska. This quarry lies in the upper portion of the Lower Harrison hori- 

 zon of Hatcher and was discovered by Mr. James H. Cook, of Agate, in the 

 year 1877. Prof. Erwin H. Barbour collected the first actual Moropus material 

 from the Agate Springs quarries in July, 1892. Mr. Harold Cook made a con- 

 siderable excavation in 1904, but it was not until 1908 that the specific name 

 Moropus cookl was given by Professor Barbour^ (January 26, 1908), thus 

 identifying the animal generically with Marsh's type of Moropus from a Some- 

 what more recent deposit.- In the meantime very extensive excavation and 

 exploration was carried on by the Carnegie Museum for Moropus, Dinohyus, 

 and Diceratherium remains, and after preliminary description the Moropus 

 skeletons were described in detail in an important memoir in 1909.^ 



These carefully conducted excavations by Mr. O. A. Peterson, under Dr. 

 W. J. Holland's direction, proved that the Agate Springs Quarry is the most 

 remarkable deposit of mammalian remains of Tertiary age that has ever been 

 found in any part of the world. Its only rival in the quantity of material 

 preserved is the mid-Pleistocene deposit of Rancho La Brea, near Los Angeles, 

 southern California. 



In 1911, through the courtesy of Messrs. James H. Cook and Harold Cook 

 and with their highly intelligent cooperation, the American Museum excava- 

 tions began under the direction of Mr. Albert Thomson, assisted by Mr. Charles 

 Earner, and continued through 1916. 



In the year 1911, after exposing a large Diceratherium area of closely packed 

 skeletal remains and securing parts of a Dinohyus skeleton, the border of a 

 great Moropus area was exposed. In the year 1912 three skeletons of Moropus 

 were secured, mingled with very abundant Diceratherium and portions of one 

 skull and skeleton of Dinohyus. During 1913 and 1914 several more skeletons 

 were found, and the outlines of a great Moropus bed were determined. In 1915 

 work was suspended. In 1916 the Moropus collections of the American Museum 

 were completed (October 29), amounting in all to seventeen skeletons. In the 

 five summers of excavation (1911-1914, 1916) an irregular area within a square 

 of about thirty-six feet yielded nearly complete skulls of ten individuals and 

 skeletal parts of seventeen more animals. 



It was at first supposed that this accumulation of bones came from the drift- 

 ing of a very large number of decomposing skeletons, but the early years of 

 careful work soon revealed the very important fact that the greater part of 

 this skeletal material belongs to a number of individuals. These individuals 



1 E. H. Barbour : The skull of Moropus. Nebr. Geol. Survey, vol. 3, pt. 2, 1908, pp. 

 209-216, pis. 1-2. figs. 1-5. 



~ The type of Moropus elatus Marsh has recently been determined by Mr. Harold Cook 

 as of Upper Harrison age. 



3 W. .T. Holland and O. A. Peterson : The osteology of the Chalicotheroidea, with spe- 

 cial reference to a mounted skeleton of Moropus elatus Marsh now installed in the 

 Carnegie Museum. Mem. Carnegie Mus.. vol. iii. no. 2. .Tan. 17. 1914. pp. 189-406. pis. 

 xlviii-lxxvii. tigs. 1-113. 



