A biochemical analysis of a rare Clovis-era stone tool cache recently unearthed in the city limits of Boulder, Colorado, in US, indicates some of the implements were used to butcher ice-age camels and horses that roamed North America until their extinction about 13,000 years ago.

The study, conducted by University of Colorado researchers, is the first to identify protein residue from extinct camels on North American stone tools and only the second to identify horse protein residue on a Clovis-age tool.

According to CU-Boulder Anthropology Professor Douglas Bamforth, who led the study, the cache is one of only a handful of Clovis-age artifact caches that have been unearthed in North America.

"The Clovis culture is believed by many archaeologists to coincide with the time the first Americans arrived on the continent from Asia via the Bering Land Bridge about
13,000 to 13,500 years ago," he said.

"Named the Mahaffy Cache after Boulder resident and landowner Patrick Mahaffy, the collection is one of only two Clovis caches that have been analyzed for protein residue from ice-age mammals," he added.

In addition to the camel and horse residue on the artifacts, a third item from the Mahaffy Cache is the first Clovis tool ever to test positive for sheep, and a fourth tested positive for bear.

The Mahaffy Cache consists of 83 stone implements ranging from salad plate-sized, elegantly crafted bifacial knives and a unique tool resembling a double-bitted axe to small blades and flint scraps.

Discovered in May 2008 by Brant Turney, head of a landscaping crew working on the Mahaffy property, the cache was unearthed with a shovel under about 18 inches of soil and was packed tightly into a hole about the size of a large shoebox.

"It appeared to have been untouched for thousands of years," Bamforth said.

Although the surface of the house lot had been lowered by construction work over the years, an analysis of photos from the Mahaffy Cache excavation site by CU-Boulder geological sciences Emeritus Professor Peter Birkeland confirmed the approximate age of sediment layer containing the Clovis implements.

The site appears to be on the edge of an ancient drainage that ran northeast from Boulder's foothills, according to Bamforth.

"The idea that these Clovis-age tools essentially fell out of someone's yard in Boulder is astonishing," he said.

"But, the evidence I've seen gives me no reason to believe the cache has been disturbed since the items were placed there for storage about 13,000 years ago," he added. (ANI)