Cornerstone communities fossil
Fossils of mammoths, bison and horses were discovered at a building site near San Diego  Cornerstone Communities Facebook

A building site designated for new houses has been home to Ice Age fossils for the past 200,000 years, it was learned after construction workers found ancient bones in southern California. The prehistoric remains of a bison, mammoths, horses and turtles were discovered when construction began on the site in Carlsbad, north of San Diego.

The fossils are aged between 50,000 and 200,000 years old and are from the Pleistocene Epoch, also known as the Ice Age. Tom Deméré, curator of palaeontology at the San Diego Natural History Museum, said in a statement on the Facebook page of Cornerstone Communities, the construction firm: "It's really an exciting project in terms of the geology and palaeontology.

"The fossils have the potential to tell us a great deal about the climate, the environment, (and) the ecology of that time when they were living. They are direct connections with the past, an ancient ecosystem that was once common here. We can understand how climates can change by studying these ancient ecosystems."

The discovery of a bison fossil – which includes a skull and "partial skeleton" – is only the second that has been discovered in San Diego, although they have not been able to place the exact species yet. Additionally, the remains of at least two Columbian mammoths were discovered at the site.

Every time a fossil is discovered there, the construction workers halt what they are doing temporarily – although the bosses don't seem to be objecting. "I said, 'Take your time, this is kind of cool,'" said John Suster of Cornerstone Communities.

Cornerstone CEO Ure Kretowicz added: "They do a (plaster)cast in place, and then remove it. We stop everything or go grade another area on the site. Once they're gone, we start up again."