For decades, animal tracks thought to have been made by a primate or ape cousin of humankind were thought to have been made by another species. New research shows that they may have been made by an early human ancestor.
Researchers from Arizona State University, using a technique that uses a technique to date chemical compounds at a depth of two feet, determined that the prints were made by an early hominin –- an ape-like species with a large brain thought to have roamed the Americas about two million years ago. This is the first time traces of a species have been found on prints made 1.3 million years ago at the Evolutionary Waymark Project, a geological treasure trove in Colorado known as the formation of the Long Waymark.
These prints, known as Bakibowuts, have become known as “the bear prints” because they resemble primitive African bear tracks but they are also backward-facing. These backs should have been made by a primate or ape, as many other bears make this kind of back-tracking.
The researchers at ASU used radiocarbon dating on the tracks and found that they were some 2.9 million years old, which they considered too young to have been made by a hominin. This is the first case of H. sapiens, the earliest hominin in the Americas, being identified as the source of a bear-like animal in fossilized dioramas.
These prints are about six-and-a-half times the size of a modern bear, said Scott Vitrone, a professor of planetary sciences and geology at ASU. He is the author of a paper about the new research, which will be published in the July 20 issue of American Scientist.
Although Vitrone and his colleagues confirmed that the prints were from a primate or ape ancestor, it remains controversial whether they are older than 6 million years, which would have been recognized as the rise of humans.
Vitrone believes that the prints have reached this age because traces of a substance called dihydroxy-vinegaroline, which most likely belongs to a primate diet, are also in the prints. (Vitrone had read an article on this in The New York Times in 2008, but he did not know at the time that some of the print’s traces also matched a natural compound).
The neodymium iron compound it is made of is rare and expensive –- more than $1,000 a ton.
Vitrone has estimated that the prints could be from about 6 million years ago. Based on previous human and primate fossils, including 150 million-year-old hominin bones from the Tarapoto well in Peru and bones from the Zaire pit from the same time, it is possible that a roughly 6 million-year-old hominin was among the competitors that were wiped out by the Pan-American worm.
But there are also microbes that are about that age and are found in places where the prints are found.
Perhaps these bacteria, which do not have a taste for the chemicals that dihydroxy-vinegaroline is made of, end up on these prints and leave traces behind, Vitrone said. Or maybe that’s just another reason why they are not much like the bear prints.