LOWER MIOCENE, UNITED STATES: NEBRASKA.
In the territory of Nebraska, on the Upper Missouri, near the Platte River,
latitude 42 degrees N., a tertiary formation occurs, consisting of white
limestone, marls, and siliceous clay, described by Dr. D. Dale Owen (David Dale
Owen Geological Survey of Wisconsin etc. Philadelphia 1852.), in which many
bones of extinct quadrupeds, and of chelonians of land or fresh-water forms, are
met with. Among these, Dr. Leidy describes a gigantic quadruped, called by him
Titanotherium, nearly allied to the Palaeotherium, but larger than any of the
species found in the Paris gypsum. With these are several species of the genus
Oreodon, Leidy, uniting the characters of pachyderms and ruminants also;
Eucrotaphus, another new genus of the same mixed character; two species of
rhinoceros of the sub-genus Acerotherium, a Lower Miocene form of Europe before
mentioned; two species of Archaeotherium, a pachyderm allied to Chaeropotamus
and Hyracotherium; also Paebrotherium, an extinct ruminant allied to
Dorcatherium, Kaup; also Agriochoerus, of Leidy, a ruminant allied to
Merycopotamus of Falconer and Cautley; and, lastly, a large carnivorous animal
of the genus Machairodus, the most ancient example of which in Europe occurs in
the Lower Miocene strata of Auvergne, but of which some species are found in
Pliocene deposits.
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