. The age of mammals in Europe, Asia and North America. Mammals, Fossil; Paleontology. 210 THE AGE OF MAMMALS tortoises (Testudinata), as analyzed by Hay/ furnish important proof of prevailing dry land conditions on the great plains. How long previously such conditions had set in it is impossible to say. In the entire Oligocene and Miocene beds of the great plains only six species of water-living turtles have thus far (1907) been recorded, and these are probably from river channel sandstones, as contrasted with a very much larger number of land-living tortoises, chiefly from fine clay deposits
. The age of mammals in Europe, Asia and North America. Mammals, Fossil; Paleontology. 210 THE AGE OF MAMMALS tortoises (Testudinata), as analyzed by Hay/ furnish important proof of prevailing dry land conditions on the great plains. How long previously such conditions had set in it is impossible to say. In the entire Oligocene and Miocene beds of the great plains only six species of water-living turtles have thus far (1907) been recorded, and these are probably from river channel sandstones, as contrasted with a very much larger number of land-living tortoises, chiefly from fine clay deposits. The upland testudi- nates include in the White River group (Lower to Upper Oligocene) eight species of land tortoises {Stylemys, Testudo). Remains of crocodiles have been recorded (Loomis) - in river channel beds of Lower Oligocene age. Physiographic conditions. — The general conditions of Oligocene life in the plains region have already been pictured in the early part of this chap- ter (p. 179), and we may now review the characters of each subdivision of the Oligocene more in detail. Lower Oligocene, Lower White River, or Chadron Formation, TiTANOTHERIUM ZoNE This takes us at once into one of the grandest and most famous of mammal-bearing horizons, the 'Titanotherium Beds' of Leidy and Hayden,. ^^^,^ in fin Fig. 98. — In the ' Big Badlands' of South Dakota ; Lower and Middle Oligocene. Lower : Titanotherium Zone including channel beds, a river formation. Upper: Oreodon Zone, a flood-plain. Photograph by American Museum of Natural History, 1907. ^ Hay, O. P., The Fossil Turtles of North America. Publ. Carneg. Inst., Washington, no. 75. 4to, 1908. ' Loomis, 1904, op. cit. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Osborn, Henry Fairfield, 1857-1935. New York, The Macmillan Company
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectpaleontology, bookyea
