North of Mexico, there are no modern primate species native to North America. It wasn't until humans arrived on the shores of today's United States and Canada that our taxonomic order had any representation on the bulk of the continent in the modern era.
So when paleontologists working in Wyoming recently unearthed the most ancient fossil evidence of a primate ever found, it was quite the jolt. Could primates have first evolved in North America, migrated across the world, and then disappeared from their ancestral homelands? Could the arrival of humans in North America have represented, in a roundabout way, our taxonomic order coming home?
Right now, this appears to be the case. The fossil itself belongs to a member of the Teilhardina genus, a group of tiny, mouse-sized primates that were extremely plentiful in the Paleocene-Eocene Thermal Maximum (PETM), a brief geological period that occurred about 55 million years ago. They are widely considered to be the earliest common ancestor of all living primates.
North America was certainly part of the ancient range of Teilhardina, which can also be found across Europe and Asia, but until now the oldest known Teilhardina came from Asia. So scientists have long assumed that the genus, and thus all primates, first emerged there.
Needless to say, the latest finding throws that theory up in the air, reports Phys.org.
"The scientific conclusion is 'We just don't know,'" said Paul Morse, the study's lead author. "While the fossils we've found potentially overturn past hypotheses of where Teilhardina came from and where it migrated, they definitely don't offer a clearer scenario."
The Wyoming specimen was dated using a combination of factors that included a careful study of the fossilized dentition of the genus, and how that dentition transitioned in form between the different species. The most precise dating mechanism, though, comes from the carbon signature of the fossils, which can place them definitively on a timeline within the PETM, the period when they lived.
It also so happens that the site in Wyoming where the fossil was recovered, Bighorn Basin, is also probably the best preserved place in the world with demarcated geological layers that fall within the PETM.
Interestingly, the PETM was a remarkable period of time in geological and climate history, marked by a global temperature that was 8 degrees Celsius hotter than temperatures today, sparked by a rapid carbon release into the atmosphere. It was comparable to the period of global warming that we see today, except that the amount of released carbon during the PETM was a modest 0.2 gigatonnes per year (at peaks of 0.58 gigatonnes), compared to the whopping 10 gigatonnes per year that are released by humans today. During the PETM, the Earth became essentially ice free, and sea levels surged by 220 feet.
It's chilling to think that such a period of global warming may have created the environment that allowed our primate ancestors to first evolve, and that global warming in modern times, by contrast, threatens to endanger so many species. Natural global warming might have ushered us in, and unnatural, anthropogenic global warming might be what ushers us out.
It's a lesson that tiny Teilhardina might inadvertently teach us, about the volatile nature of biological systems, and the fragilities by which they can shift. If these ancient primates represented one bookend for our taxonomic order, hopefully modern global warming won't be the other.
"A changing planet has dramatic effects on biology, ecosystems and evolution. It's part of the process that has produced the diversity of life we see today and mass extinctions of life that have happened periodically in Earth's history," said Jonathan Bloch, study co-author. "One of the unexpected results of global warming 56 million years ago is that it marks the origin of the group that ultimately led to us. How we will fare under future warming scenarios is less certain."