A controversial find could rewrite the history of humans in North America.
Archaeologists claim to have found evidence an unknown species of human was living on the continent as early as 130,000 years ago – 1115,000 years earlier than previously thought.
Researchers discovered the butchered remains of an enormous mastodon in San Diego, with evidence of chips and fractures made by early humans – but they admit they don’t know if they were Homo sapiens, Homo erectus, Neanderthals, or something else.
The findings could dramatically revise the timeline for when humans first reached North America, although many researchers are sceptical of the find, claiming there are issues with the dating technique used and ‘many questions’ over the research.
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In 1992, archaeologists discovered the fossilised remains of an enormous mastodon in San Diego – a mammoth-like creature that roamed North America 130,000 years ago
WHO WERE THEY?
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.
No remains of any individuals were found.
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.
Bones, tusks and molars – many of which had signs that they were deliberately damaged – were found deeply buried alongside large stones that appeared to have been used as hammers and anvils.
Ms Judy Gradwohl, CEO of the San Diego Natural History Museum, said: ‘This discovery is rewriting our understanding of when humans reached the New World.
‘The evidence we found at this site indicates that some hominin species was living in North America 115,000 years earlier than previously thought.
‘This raises intriguing questions about how these early humans arrived here and who they were.’
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.
No remains of any individuals were found.
Whoever they were, they could have arrived by land or sea.
They might have come from Asia via the Beringea land bridge that used to connect Siberia to Alaska, or maybe come across by watercraft along the Beringea coast or across open water to North America, before turning southward to California, Holen said in a telephone interview.
Holen and others present their evidence in a paper released Wednesday by the journal Nature.
HOW DO THEY KNOW HUMANS BUTCHERED THE BONES?
The researchers believe they have enough evidence to conclude that the damage to the bones was made by humans and not animals.
The researchers believe they have enough evidence to conclude that the damage to the bones was made by humans and not animals. Pictured is a close-up view of a spirally fractured mastodon femur bone
The bones were found in two rough piles, each with two or three large rocks measuring 10 to 30cm across.
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.
The surface of a mastodon bone showing half impact notch on a segment of femur. Unfortunately, the finding poses a lot more questions than answers, and the researchers have been unable to determine who these early people were
This diagram shows a schematic of a mastodon skeleton. The bones and fragments coloured in were those found at the site
‘We have also excavated sites in the central great plains for the past 25 years that have the same types of fracture patterns on mastodon limb bones.
‘Again, they’re found in very fine-grain geological deposits.
‘So we can eliminate all of the natural processes that break bones, such as carnivore chewing, or other animals trampling on them.’
‘So we can eliminate all of the natural processes that break bones, such as carnivore chewing, or other animals trampling on them.’
Unfortunately, the finding poses a lot more questions than answers, and the researchers have been unable to determine who these early people were.
Not surprisingly, the report was met by skepticism from other experts who don’t think there is enough proof.
However, many are sceptical of the find, and the dating methods used.
‘This is a really extraordinary claim,’ Jean-Jacques Hublin at the Max Planck Institute for Evolutionary Anthropology in Leipzig told The Guardian.
‘There are questions about everything.’
‘If the results stand up to further scrutiny, this does indeed change everything we thought we knew,’ said Chris Stringer of the Natural History Museum in London. Neanderthals and Denisovans are the most likely identities of the visitors, he said.
The bones were found at the Cerutti Mastodon site in San Diego, on the west coast of California
But ‘many of us will want to see supporting evidence of this ancient occupation from other sites, before we abandon the conventional model of a first arrival by modern humans within the last 15,000 years,’ he wrote in an email.
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.
They could have been Neanderthals – a species that was known to be living in Africa and Europe at the time.
Until recently, the oldest records of human sites in North America were about 15,000 years old.
But the fossils from the Cerutti Mastodon site were found embedded in fine-grained sediments that had been deposited much earlier, during a period long before humans were thought to have arrived on the continent.
Dr Tom Demere, an author of the study, said: ‘When we first discovered the site, there was strong physical evidence that placed humans alongside extinct Ice Age megafauna.
Richard Cerutti (left) and Dr Tom Deméré (right) are pictured together holding one of the mastodon fossil tusks
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A drawer full of Cerutti Mastodon site fossils in the San Diego Natural History Museum’s Paleontology Collection Room
‘This was significant in and of itself and a first in San Diego County.
‘Since the original discovery, dating technology has advanced to enable us to confirm with further certainty that early humans were here significantly earlier than commonly accepted.’
Since its initial discovery in late 1992, this site has been the subject of research by scientists to date the fossils accurately and evaluate microscopic damage on the bones and rocks.
In 2014, Dr James Paces, a research geologist with the US Geological Survey, used radiometric dating methods to determine that the mastodon bones were 130,000 years old.
A view of two mastodon femur balls, one faced up and once faced down. The neural spine of a vertebra exposed (lower right) and a broken rib (lower left)
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
The researchers believe they have enough evidence to conclude that the damage to the bones was made by humans and not animals.
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.
Bones, tusks and molars – many of which had signs that they were deliberately damaged – were found deeply buried alongside large stones that appeared to have been used as hammers and anvils
This 3D animation shows how mastodon bone fragments, which were discovered separate from one another, can refit to form a larger bone fragment. The fragments were all found with broken bones and rock