A RECORD OF THE EXTINCT HORSE PLIOHIPPUS FROM THE MARINE PLIOCENE OF LOS ANGELES, CALIFORNIA
by Jack D. Mount¹
During July, 1969, Mr. Richard V. Betancourt, Los Angeles, California, brought to the Geology Department of California State College, Los Angeles (CSCLA), the fossil tooth of a horse which he had collected near his home. I have long had a great interest in the geology and paleontology of the Repetto Hills and my interest in this tooth increased sharply when, after discussion with Mr. Betancourt about the collecting locality, it was revealed that the tooth was found in the marine Pliocene sediments of the Repetto Hills. The fossil tooth was given to Professor George E. Jakway, a vertebrate paleontologist in the Zoology Department of the college, for identification.
The collecting locality is in the southwest Repetto Hills which are located in Los Angeles near the eastern limit of the city. The horse tooth was found under the Edison tower at the rear of Davidson Brickyard, the site being 1020 feet due east of the NW corner of section 32, T 1 S,, R 12 W, Los Angeles Quadrangle (1953 edition). The site was registered as CSCLA locality 624.
The horse tooth was collected from the Fernando Formation which in the Repetto Hills consists of a monotonous sequence of about 5,800 feet of siltstone with some sandstone and a minor amount of conglomerate (Yerkes and others, 1965). CSCLA 624 is near the top of the formation in a foot thick bed of pebble conglomerate which dips 90° and strikes eastwest. The conglomerate is unsorted and ungraded and contains masses of broken mollusk shells. The siltstone contains deepwater foraminifera and a paucity of larger fossils (Troxel, 1954). The conglomerates are evidently redeposited sediments attributable to mass underwater movement. The sediments probably were first deposited in nearshore areas and later slid to the base of a steep underwater slope. These types of sediments are termed a gravitite by Natland (1967).
Fig. 1. Left upper molar of Pliohippus sp. from CSCLA Locality 624, Los Angeles, California, Pliocene.
The fossil tooth is a left upper molar and was identified by Professor Jakway as belonging to the extinct horse Pliohippus (Figure 1). Pliphippus was an early advanced grazing horse and was essentially a single-toed horse, the outer toes being no longer functional (Stock and Howard, 1963).
Subsequent to the initial discovery of the fossil tooth, I returned to the site and collected a small molluscan fauna which consists of the following forms.
The small molluscan fauna indicates a late Pliocene age based on a two fold division of the Pliocene and is similar to faunas of that age from the Los Angeles basin.
The closest occurence of Pliohippus is the Mount Eden Fauna from the San Timoteo badlands near Beaumont in Riverside County (Frick, 1921). This fauna is dated as Hemphillian age (middle Pliocene of the vertebrate paleontologists) (Savage and others, 1954).
Pliohippus has also been collected from the Tick Canyon Formation of the eastern Ventura basin which has been dated as Clarendonian age (early Pliocene) (Savage and others, 1954). However, because of the age of the molluscan fauna, the tooth from CSCLA 624 probably represents Hemphillian age.
Pliohippus teeth occur in the marine Pliocene Etchegoin Formation of the Kettleman Hills- Coalinga district (Durham and others, 1954) which is correlative with at least a part of the Fernando Formation.
Durham, J.W., Jahns, R.H., and Savage, D.E., 1954, Marine-nonmarine relationships in the Cenozoic section of California, in Geology of southern California: Calif. Div. Mines Bull. 170, ch.3, p.59-71.
Frick, C. 1921, Extinct vertebrate faunas of the badlands of Bautista Creek and San Timoteo Canyon: Univ. Calif. Dept. Geol. Sci. Bull., vol.12, p.277-424.
Natland, M.L., 1967, New classification of water-laid clastic sediments (Abst.): Am. Assoc. Pet. Geol. Bull., vol.51, no.3, pt.1, p.476.
Savage, D.E., Downs, T., and Poe, O.J., 1954, Cenozoic land life of southern California, in Geology of southern California: Calif. Div. Mines Bull. 170, ch.3, p.43-58.
Stock, C., and Howard, H., 1963, The ascent of Equus: Los Angeles Co. Mus. Sci. Ser., no.8, 38 p.
Troxel, B.W., 1954, Geologic guide for the Los Angeles basin, southern California, in Geology of southern California: Calif. Div. Mines Bull. 170, Geologic Guide No.3. 46 p.
Yerkes, R.F., McCulloh, T.H., Schoellhamer, J.E., and Vedder, J.G., 1965, Geology of the Los Angeles basin, California - an introduction: U.S. Geol. Survey Prof. Paper 420-A, 57 p.
¹Department of Geology, California State College, Los Angeles.
Return to Paleontology Resources page
Return to first page of Jack's Home Place