The tar deposits of Rancho La Brea at Los Angeles (California) yielded an exceptionally well preserved and rich fossil material. So rich that for most limb bones I have measured only the left-sided ones. Otherwise left side (G) or right side (D) are specified in the tables. Nearly all fossils are preserved at the George C. Page Museum close to the site itself ; other may be found at the Los Angeles County Museum (LACM), at the American Museum of Natural History (NY), and at the University of Calfornia Museum of Paleontology (UCMP), Berkeley. Los Angeles specimens are labeled LACM, or merely bear field indications (pit number ; quadrate ; depth (for instance "3 F5 18-19")). The fossils date to Late Pleistocene, probably till ca. 40.000 BP.
Although Leidy had not really defined a type in his 1865 publication, the large equid of Rancho La Brea is commonly named Equus occidentalis. A caballine species (E. pacificus of Gidley) may be present also (Pichardo 2006) ; at least it seems to be represented by the associated upper and lower dentitions UCMP 9G 14-10,5 dated at 12.000 or 35.000 ans (see figure).
The number of young individuals is remarquable : there are 62 juvenile upper dentitions for 13 adult ; 41 third epiphysated metacarpals and metatarsals for respectively 22 and 14 not epiphysed.
E. occidentalis resemble South American Amerhippus by the constant lack of infundibula on les lower incisors. Unlike them, however, its basi-cranial proportions are not caballine.
– PICHARDO M. 2006. Update of Equids in paleoindian time. 9th ICAZ Conference, Durham 2002. In : Equids in Time and Space, Marjan Mashkour ed., 13 : 31-48, 8 figs, 2 tabl. Oxbow Books.
– STOCK Chester. 1972. Rancho La Brea, arecord of Pleistocene life in Calofornia. Los Angeles County Museum of Natural History, Science Series 20, Paleontology 11, 81pp.
Other similar tar deposits were excavated at Mac Kittrick, Kern County, California ; fossils are less abundant and not so well preserved. Most may be fond at the LACM (CIT 138) ; other at the UCMP.