Roughly 56 million years ago, a tiny little primate no bigger than a mouse scurried about the forests of Asia, Europe, and North America. But where did it come from? It has long been thought that the critter, known as Teilhardina, first popped up in China before expanding its range across the continents. But new research casts doubt on this idea.

Teilhardina is actually a genus that contains various different species from different locations. For example, remains of Teilhardina brandti have been found in the US, while teeth and bones of T. asiatica have been uncovered in Asia. What’s so exciting about this critter is that it’s the oldest known ancestor of modern primates, which, along with monkeys, lemurs, and apes, include us.  

The new study, published in the Journal of Human Evolution, suggests that T. brandti, a species local to what is now Wyoming, is as old, if not older, than its Asian counterpart. This suggests that Teilhardina may actually have originated in North America, not Asia as was previously thought.

However, the researchers themselves are quick to point out that their research doesn’t conclusively solve the puzzle.  

“The scientific conclusion is ‘We just don’t know,’” said Paul Morse, the study’s lead author, in a statement. “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.”

Nevertheless, the researchers found that some of T. brandti’s features are just as primitive as those of its Asian relatives. They conducted the most comprehensive analysis of T. brandti ever, looking at 163 teeth and jaws.

Teeth are particularly useful to palaeontologists as they tend to preserve better than bone, and are suggestive of an animal’s diet, size, and even its age. T. brandti was first described back in 1993 when a single tooth was discovered. Now, thanks to a great deal of patient digging, much more evidence has been uncovered and we have a clearer picture of the ancient primate.

One particular specimen – a little piece of jaw with teeth still attached – is what sparked the new research.

“Jon and I started arguing about the alveoli” – empty tooth sockets – “and how they didn’t look right at all,” said Morse. “By the end of the day, we realized that specimen completely overturned both the species definition of T. asiatica and part of the rationale for why it is the oldest Teilhardina species.”

The study has also resulted in a reshuffling of the Teilhardina family tree. There are now six species, rather than nine, and two species have been added to a new genus call Bownomomys.

While more evidence is needed to definitively tell us whether the American or Asian species came first, we now know that they are “essentially equivalent in age”. We’ll have to wait to find out exactly where our tiny ancient ancestors first arose.