Tetraclaenodon puercensis

Horse Ancestry
Submitted by Ben Nafus
Paleo Artwork By Ben Nafus

Looking into the hazy origins of horses found among the various sources being offered by a number of authorities, I was startled to find that the ancient Paleocene swamps of what was to become Kern County was the stomping ground of the horse ancestor, Tetraclaenodon puercensis, West (1970, 1976). This animal stems from the Order Condylarthra that was among the earliest of mammals that ran from - and with - the Mesozoic dinosaurs. After the KT (Cretaceous - Tertiary) event and the extinction of the dinosaurs, some sixty five million years ago, the Condylarths, some five or six groups of them, began their diversity in North America and Europe, these two continents were still not yet separated.

This T. puercensis was found in 1954 by F. E. Corwin, northeast of Black Mountain, just east of Red Rock State Park in Kern County. The fossil consists of "the right and left lower jaws of a single individual" within a ironstone concretion found in Quaternary alluvium of Golar formation origin. The age of these rocks are either Torrejonian (medial Paleocene) or early Tiffanian (early late Paleocene), about 60 million years in age. Comparable fossils of this group have been found in New Mexico, Wyoming and Montana.

Other contemporary Golar Formation fossils such as turtle shells, nonmarine mollusks and crocodile teeth suggests that the climate was subtropical and the lush environment was like that of present Florida: swamps with densely forested hammocks and low islands that were within a short distance of the Pacific Ocean. This particular area would have been subjected to a very heavy annual rainfall, estimated to be up to 80 inches a year! Today, this entire region is part of the El Paso Mountains north of the Mojave desert in northeastern Kern County. The fact that this arid location is now more than 250 miles east of the Pacific Ocean and on the eastern slopes of the Sierra Nevada range adds to the fossil's geologic history.

T. puercensis was not a large animal: it was about the size of a sheep, with a long tail, short legs with feet that were free to rotate laterally. Each foot had five hoofed digits. The primal brain was small, "Condylarths are so primitive that it is difficult to identify characteristic features. They are small , quadrupedal, five-toed (with hoofs), and usually have a full dentition. Their most distinctive features are the cheek teeth, which are squarish, have four primary cusps and are capable of grinding vegetation. In other features, they resemble primitive carnivores (both groups share a common ancestor)." (The Encyclopedia of Prehistoric Life, edited by Rodney Steel & Anthony Harvey, Gramercy Publishing Co.)

References cited: Mammal Evolution, RJG Savage & MR Long, Facts of File Pub. The Macmillan illustrated Encyclopedia of Dinosaurs and Prehistoric Animals, by Dougal Dixon, Barry Cox, R.J.G. Savage, Brian Gardiner and Dr. Malcolm C. McKenna. American Museum of Natural History. Basin Analysis and Paleocene and Eocene Golar Formation, El Paso Mountains, CA; Editor, Brent F. Cox, USGS.

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