Tarsiers just don’t fit in! There are three species of tarsier, and scientists don’t know how to classify them. Yes, they’re definitely primates, but are they prosimians like lemurs and lorises or are they anthropoids like monkeys, apes and humans?
At first glance, tarsiers appear physically similar to a loris or lemur. Take a look at this photo comparing a tarsier with a loris. They have big eyes, a tiny body, large ears, an unfused mandible and a grooming claw. This is why tarsiers are traditionally classified as prosimians. However, further study suggest that they may actually be more closely related to the anthropoids than initially believed.
One of the major differences between anthropoids and prosimians is the rhinarium. A rhinarium is the moist, hairless part of the nose of most animals. Prosimians have this; their noses are similar to those of dogs or raccoons. Anthropoids, on the other hand, do not have a rhinarium. Neither does the tarsier.
Another common prosimian trait that tarsiers and anthropoids both lack is the tooth comb. This is a long, flat set of forward-angled teeth used for grooming. Here’s a picture of the tooth comb in a lemur.
Biochemically speaking, tarsiers seem to actually share more similarities with anthropoids than prosimians regardless of how they look on the outside. Stranger, though, is the fact that on a chromosomal level, they are very distinct and fit neither group.
A tarsier’s chromosomes aren’t the only traits that set it apart from the rest of the primates. Its enormous eyes probably stand out the most among all their traits. They’re big because tarsiers are nocturnal (which itself is rare, but not unheard of, among primates), but the odd thing about them isn’t their size. It’s the fact that they are immobile in the eye sockets. It cannot move its eyes, so to compensate, it has the ability to rotate its head 180 degrees, much like an owl. This is not seen in other primates. They are also entirely carnivorous, which is unusual because primates tend to be omnivores.
This little primate may be a taxonomic problem, causing debate among primatologists and biologists on where it belongs; but it’s still a fascinating creature to learn about. It may not have a set place in our classification system just yet, but in the islands of South East Asia, the tarsier fits in fine.
Jurman, Robert et. al. The Essentials of Physical Anthropology
Tarsiers at the Wayback Machine