Isn t carbon dating used dinosaur bones
Some skeptics suggested alternative explanations about the material excavated beginning in 1992 at a freeway construction site, suggesting the bones may have been broken recently by heavy construction equipment rather than by ancient humans.
The researchers are unsure who these humans were, or where they went to after butchering the mastodon bones.
Holen and others present their evidence in a paper released Wednesday by the journal Nature.
The bones were found in two rough piles, each with two or three large rocks measuring 10 to 30cm across.
Dr Steve Walsh is pictured holding a mastodon molar fragment found under a rock anvil'So we can eliminate all of the natural processes that break bones, such as carnivore chewing, or other animals trampling on them.' Previous studies have suggested that humans migrated to America via a land bridge from Asia to North America, although the researchers are unsure if this is still the case.
This 3D animation shows a mastodon bone impact flake found at the Cerutti Mastodon Site.
The earlier date means the bone-smashers were not necessarily members of our own species, Homo sapiens.
The researchers speculate that these early Californians could have instead been species known only from fossils in Europe, Africa and Asia: Neanderthals, a little-known group called Denisovans, or another human forerunner named Homo erectus.'The very honest answer is, we don't know,' said Steven Holen, lead author of the paper and director of the nonprofit Center for American Paleolithic Research in Hot Springs, South Dakota. The mastodon remains were discovered at the Cerutti Mastodon site in San Diego by palaeontologists from the San Diego Natural History Museum during routine work in 1992.
These early humans are known as the Clovis culture and were distinguished by the fine fluted stone points they made for weapons.Around 16,000 years ago, they appear to have then entered North America and rapidly spread down the coast.However, archaeologists recently found evidence that suggests early settlers were living in the Americas up to 19,000 years ago.The scientists believe the stones are too heavy to have been carried there in the flow of a stream, and instead suspect they were carried by humans for use as hammerstones and anvils to break the bones apart.During a press briefing, Dr Steve Holen, lead author of the study, said: 'We have conducted two experiments breaking elephant bones with large rock hammers, and we produced exactly the same kinds of fracture patterns that we see at the Cerutti Mastodon site.