NEW REMAINS OF MIDDLE MIOCENE EQUIDS FROM THE CAJON VALLEY FORMATION, SAN BERNARDINO NATIONAL FOREST, SAN BERNARDINO COUNTY, CALIFORNIA

The Cajon Valley Formation, located partially in the San Bernardino National Forest, spans the late Hemingfordian and early Barstovian NALMA. Previously considered part of the Punchbowl Formation, the Cajon Valley Formation has been excavated by various institutions since the 1970s, most notably by the University of California, Riverside (UCR) and San Bernardino County Museum (SBCM). The majority of these fossil collections are now housed at the University of California, Berkeley, SBCM, and Western Science Center (WSC), the last of which began work in 2018. Excavation of a quarry in the Cajon Valley Formation by WSC yielded new fossil material including remains of three equid taxa: Archaeohippus mourningi, Scaphohippus sumani, and the first record of “Parahippus” brevidens south of North Coalinga. Of particular interest is S. sumani; the genus Scaphohippus currently consists of two species: S. sumani and S. intermontanus, both of which were originally included in the genus Merychippus (Merriam 1915). Both species overlap in time. We propose that previously cited differences in plication morphology and wear patterns are not sufficient to distinguish two taxa. We assert that based on observed full palates of both species, there is actually only one species: Scaphohippus sumani, which has taxonomic priority.“Parahippus” brevidens is identified from an upper molar that closely resembles the morphology of the holotype as well as referred specimens of P. brevidens from the Mascall Formation in Oregon. The presence of “P.” brevidens in the Cajon Valley Formation represents a range extension for the taxon of over 400 km.