The fossilized remains of horses and camels dating back up to 12 million years have been unearthed in Oklahoma.
The fossils were unearthed by a sharp-eyed heavy-machine operator working for a Houston, Texas-based oil firm, Apache Corp.
The worker had scraped away about 20 feet of earth in July in the Packsaddle Wildlife Management Area, just north of the Canadian River in Ellis County, when he spied the fossils.
Experts were called in, with a team of paleontologists and archaeologists so far uncovering 13 separate pits containing fossil bones.
The Oklahoman newspaper reports that the fossils of extinct species date from five million to 12 million years ago.
The highlight to date has been the unearthing of a well-preserved horse skull far tinier than its present-day descendant.
The remains are typical prey animals from the Late Miocene period.
The curator of vertebrate paleontology for the Sam Noble Oklahoma Museum of Natural History, Nicholas Czaplewski, said it could take years to sort through the fossil discoveries.
The remains will be compared with known species whose fossil remains have already been identified in the region. The new finds may help experts learn about the anatomy of existing species.