Vertebrate Fossils From The Coso Formation

Coso Mountains, Inyo County, California

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Click on the image for a larger picture. Here are some fossil teeth and a couple of limb bone fragments from the Pliocene Coso Formation. All specimens came from the extinct one-toed Pliocene horse, called scientifically, Eguus simplicidens (it still retained vestiges of two side toes from earlier three-toed horses)--this is the famed Hagerman Horse, named for its spectacular occurrence at Hagerman Fossil Beds National Monument in Idaho, a species that vertebrate paleontologists consider the earliest member of the genus Equus, includes all present-day equids, such as modern horses, zebras, Grévy-zebras, wild asses, the Asiatic wild ass and the Przewalski horses; it appears to have been about the size of a modern Arabian horse with a decidedly zebra-like body, in general appearance--as a matter of fact, the Hagerman Horse is now believed to have been more closely related to the modern Grevy Zebra than to a horse. Specimens are roughly three million years old. For scale, the horse jaw segment at upper left is 70 millimeters long.

Click on the image for a larger picture. This is a different view of all but one of the fossil horse teeth in the first image (the tooth at lower right in the top picture does not appear in the second image). Teeth and miscellaneous bones of the extinct singe-toed horse Equus simplicidens are by far the most common vertebrate fossils encountered in the Coso Formation badlands, Coso Range, Inyo County, California. Specimens are roughly three million years old. For scale, the horse jaw segment at upper middle is 70 millimeters long.

Click on the image for a larger picture. Here is a closer look at the horse jaw segment seen in the first two images. It came from the Hagerman Horse, Equus simplicidens; found in the Pliocene Coso Formation, Coso Range, Inyo County, California. The specimen is roughly three million years old; 70 millimeters long in actual size.

Click on the image for a larger picture. This is a closeup of the fossil horse tooth seen at upper middle in the top image and at lower right in the second image. It is a molar from the extinct single-toed horse Equus simplicidens, found in the Pliocene Coso Formation, Coso Range, Inyo County, California. From bottom to crown, the tooth is 35 millimeters high; it is roughly three million years old.

Click on the image for a larger picture. A different perspective of the same horse molar seen in the previous picture. It's roughly three million years old and stands 35 millimeters high from base to crown. Found in the Pliocene Coso Formation, Coso Range, Inyo County, California.

Click on the image for a larger picture. Two views of the same lower jaw from the Hagerman Horse---Equus simplicidens, collected from exposures of the Pliocene Coso Formation, Coso Mountains, Inyo County, California. Equus simplicidens is considered one of the earliest known members of the genus Equus, which includes the modern horse and all other equids. Originally described as Plesippus francescana, but is now recognized as Equus simplicidens. Photograph courtesy a public domain document.

Click on the image for a larger picture. Segments of lower jaws from the Hagerman Horse---Equus simplicidens, collected from exposures of the Pliocene Coso Formation, Coso Mountains, Inyo County, California. Equus simplicidens is considered one of the earliest known members of the genus Equus, which includes the modern horse and all other equids. Originally described as Plesippus francescana, but is now recognized as Equus simplicidens. Photograph courtesy a public domain document.

Click on the image for a larger picture. Top: horse metatarsal (back foot--the longer specimen at left) and phalanges (foot bones); bottom--horse metacarpal (front foot--the longer specimen at left) and phalanges (foot bones). All from Equus simplicidens, which is considered one of the earliest known members of the genus Equus, a genus that includes the modern horse and all other equids. Originally described as Plesippus francescana, but is now recognized as Equus simplicidens. Photograph courtesy a public domain document.

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