30 



OSBORN: OLIGOCENE, MIOCENE, PLIOCENE EQUiDiE. 



Observations of Matthew on Typical Pawnee Creek, Merychippus Zone, Middle Miocene. 



All the horses known from the typical Pawnee Creek are referable to Merychippus. They are more progressive than 

 the Merychippus from the Sheep Creek or Maseall and foreshadow the distinct groups of Equidse of the Upper Miocene, 

 although all fall within the genus Merychippus. The Lower Pliocene groups more or less distinctly foreshadowed are: 



Merychippus sejunctus = Protohippus perditus group 



" paniensis = ^Merychippus calamarius group 



" sphenodus = 1 Merychippus insignis group 



" campestris = Pliohippus tnirabilis group 



" eoplacidus = Protohippus placidus group 



" proparvulus = Protohippus paruulus group 



" eohipparion = Hipparion occidenlale group 



The horses include also successive mutations of the Pawnee Creek species and forms intermediate between 

 characteristic Pawnee Creek stages, such as M. sejunctus, and those characteristic of the Niobrara and Little White River 

 region. For example, there is a form much like M. sejunctus, but large, robust, with somewhat deeper preorbital fossae, 

 heavier limbs, and long feet. There is also a form of Merychippus with limbs having the lateral digits much reduced, 

 and with moderately long-crowned teeth, to which the name Merychippus eoplacidus may be given. 



In all the typical Pawnee Creek species the milk premolars are uncemented when first erupted but acquire an imper- 

 feet coating of cement by the time they are well worn. They retain the low crowns of the milk premolars of Parahippus, 

 but the metaconule is crescentiform and more or less completely united to the crochet; the permanent molars are never- 

 theless not so elongate as in Protohippus and Hipparion. They retain most or all of the distinctive generic characters of 

 Merychippus. 



Besides the specimens referable to the typical M. sejunctus, M. labrosus, M. paniensis, M. sphenodus, M. campestris, 

 these typical Pawnee Creek beds yield the following new types: 



Type of Merychippus eoplacidus Osborn, 1918.6. 

 " " " proparvulus Osborn, 1918.7. 



" " " eohipparion Osborn, 1918.8. 



Cache Peak, Upper Levels of Monolith Series, Tehachapi, Southern California. 



The horses of this level, according to Merriam, include species comparable to Merychippus campestris and Hypohippus 

 of the typical Middle Miocene, Pawnee Creek, Col. There occur here also Dromomcryx and Merycocha?rus (Buwalda). 



" The Cache Peak fauna represents a stage in advance of that found at Phillips Ranch. The Cache Peak fauna may 

 be late middle Miocene or upper Miocene; it may furnish a transition stage between the Phillips Ranch and the Barstow 

 faunas, but it is much nearer to the Barstow than to the Phillips Ranch." 1 



Barstow, Mohave Desert, Southern California, of Upper Miocene Age (Merriam, 1917). 



As described by Merriam this horizon contains a rich horse fauna, apparently covering the transition period between 

 the typical Merychippus zone and the Protohippus zone. The equines are referred to the genera Parahippus (Archovo- 

 hippus), Hypohippus, Merychippus, and Protohippus. The true Merychippus calamarius is believed to occur here, which 

 is a late Miocene species. The horizon is regarded by Matthew as a very late phase of the Miocene, near the 

 top of the Merychippus zone, later than the typical Pawnee Creek of Colorado, and earlier than the Lower Pliocene for- 

 mation of the Niobrara River. Merriam (1917) considers it Upper Miocene. The types recorded here are: 



Type of Archccohippus mourningi Type of Merychippus (Protohippus) intcrmontanus 



Merriam, 1913. Merriam, 1915.3. 



Type of Merychippus (calamarius) sumani 1915.2. 



1 Buwalda, John P. "New Mammalian Faunas from Miocene Sediments near Tehachapi Pass in the Southern Sierra Nevada," 

 Univ. Cat. Publ. Bull. Dept. Geol, Vol. 10, No. 6, Nov. 18, 1916, pp. 75-85 (p. 83). 



