248 TEN YEARS^ PROGRESS IN VERTEBRATE PALEONTOLOGY 



Moropus, is regarded as representing the close of Oligocene life, and the 

 succeeding oreodont, Menjcocharus, is regarded as marking the opening 

 phase of the Miocene. Our knowledge of the life of these two very rich 

 zones is due to the discoveries of the Messrs. Cook, of Agate, Nebraska, 

 and the energetic work of parties from the N'ebraska, Carnegie, and 

 American Museums. This annectant Oligocene-Miocene fauna repre- 

 sents, in fact, the greatest f aunistic advance of the decade. A practically 

 unknown life period has become one of the most fully known, with an 

 abundance of complete skeletons and an overwhelming wealth of material. 



Miocene 



Ranking as next in importance to the wonderful progress in the Eocene 

 is the Miocene history of the past decade, which we owe to Hatcher 

 (1902-1904),^^ Peterson (1907), Matthew (1907), and Cook. The 

 Lower Miocene has been spoken of above as distinguished by the presence 

 of Merycochcerus and absence of Promerycochoerus and Dinohyus. This 

 fauna otherwise closely articulates with the subjacent fauna. 



The Middle Miocene is a clearly circumscribed fauna without known 

 transitions either above or below. Its correlation is chiefly the work of 

 Matthew (fauna! character, 1901), of Merriam (Mascal, 1907), of Doug- 

 lass (Madison Yalley, 1903), based on original field work and a synthesis 

 of the earlier work of Cope (1873, 1897-1898) and of Scott (Deep Eiver, 

 1895), together with a freshening discovery of new and more complete 

 forms, and many direct additions to our knowledge. The latest forma- 

 tion to be added to this correlation is the Virgin Valley of Nevada, 

 which Merriam (1911) and Gidley regard as contemporaneous or a little 

 earlier in deposition than the Mascal of Oregon, which is in the typical 

 Merydiippus zone. 



The zonal type of this Middle Miocene stage is Ticlioleptus. a short- 

 faced oreodont which, with Merycliippus and the first Proboscideans of 

 North America, ties together formations widely scattered in Oregon, 

 Montana, and Colorado. We greatly need more accurate geologic sec- 

 tions and more concise data regarding this Middle Miocene stage. 



A sharply defined as well as very long time inten^al separates the 

 Lower Miocene fauna from this Middle Miocene fauna. 



The Upper Miocene is another clearly defined faunal period, the zone 

 of Procamelus, Hipparion, and Protohippus, mammals which tie together 

 scattered river channel and flood plain deposits in Nebraska, South Da- 



" J. B. Hatcher : An Attempt to Correlate the Marine with the Non-Marine Formations 

 of the Middle West. Proceedings of the American Philosophical Society, vol. xliii, no. 

 178, Octoher-Decemher, 1004, pp. 341-364. 



