A Pliocene fauna from Western Nebraska / by W.D. Matthew and Harold J. Cook.

  • William Diller Matthew
Date:
1909
Catalogue details

Licence: In copyright

Credit: A Pliocene fauna from Western Nebraska / by W.D. Matthew and Harold J. Cook. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    Miocene or Lower Pliocene,1 but the modernization is more apparent, '['lie Archer (Alachua days) of Florida and the Rattlesnake of Oregon may represent an equivalent stage, but are too little known for satisfactory corre- lation. The Blanco fauna, so far as known, is distinctly more modem, in the relative abundance of Edentata, in absence of Oreodonts, Merycodus, Procamelus and numerous other Miocene genera; but how far the absence of these genera may be due to our limited knowledge of the fauna it is impos- sible to say. Very little is known of the Blanco horses, which would furnish the most satisfactory comparisons, but Gidley has shown that the reported occurrence of Equus in this formation is an error, the species being all of the Protohippine group and not recognizably more advanced than the Miocene horses. The Snake Creek Pliauehenias compare with those of the Blanco in size and in reduction of the dentition, although of different species. V. Descriptions of Genera and Species. Amphicyon amnicola sp. nov. Type, a lower jaw, No. 13840, with Mj_2 and alveoli of the premolars and m3. Size about equal to A. giganteus of the Middle Miocene of Europe, or .1. sinapius of the Pawnee Creek beds of Colorado, but the reduction of the premolars is further advanced than in any known species of this group. The heel of m2 is relatively narrow, and m3 is large and two-rooted, as in Amphicyon. In Dinocyon thenardi and Borophagus gidleyi, the heel of in, is broad and m3 short, one-rooted. 'Phis difference is probably generic, as it is correlated with the presence or absence of m3 in the upper jaw, the primary distinction between Amphicyon and Dinocyon or Borophagus. The reduction of the premolars appears to be as in Ursus, a two-rooted p4 with a diastema in front; but the jaw is broken off in advance of this dias- tema, so that we cannot determine tin1 presence or absence of p,. 'Flic form and proportions of the back of the jaw agree entirely with .1. giganteus. The position of the condyle is considerably above the tooth-line, instead of below it as in Ursus, and the inferior margin of the jaw is much more convex beneath the molars than in that genus. The form of the eoronoid process, so far as it is preserved, is much as in Ursus. 1 Osborn, l. r.
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