PROSIMIANS

The word Prosimian is made up of two parts: Pro, which in this case means “before” and Simian, which literally means ape. So before we get into what a prosimian is, it might help to know what features define a simian.  A simian is a scientific word to describe what you’d call the higher primates, or maybe the classic visual image that comes to mind when you hear the word monkey or ape.  Higher primates have nearly all the same physical features that you have (makes sense given than humans are simians as well). These features include color vision, relatively large body sizes and brains, and short, dry noses. Prosimians are thought to be more primitive than simians, and they are usually smaller in size than simians with a long snout ending in a wet nose like your dog and a smaller brain to body ratio than monkeys and apes. In fact, prosimians can alternatively be classified into the suborder Strepsirhini (strep-si-ree-nee) which may sound like good pasta to pair with a fruity wine but is actually a term that applies to the “wet nose” that these cute little guys and gals have. Many scientists favor this type of description for reasons we get into a little later.

Let’s get technical, technical…we want to get technical!  Let’s get into technical! Prosimians are unique among primates in that they share particular things in common with non-primate mammals, such as a tapetum, specialized scent glands, a bicornuate uterus, open eye sockets, a tooth comb, and unfused mandibles. Hmmm…that sounds very fascinating I’m sure, but let’s break those down in the style of David Letterman.  (Drumroll begins.)

Top 10 signs you’re a prosimian:

10. Your eyes glow at night when someone shines light into them. This is because of your tapetum (layer of the eye used for nocturnal vision).

9. You rub your arms, hands, head, and nether regions everywhere you go so as to communicate your status to everyone else around, mark your territory, etc.

8. You don’t care much about high def TV because you can’t see in color.

7. You’re a female and you have a heart-shaped uterus with 2 cavities, much like other, non-primate mammals.

• Confused? Grab a 7^th grade health book to see what the human and typical simian uterus looks like.  Prosimian uteri look quite different!

6. Your eyes are relatively large to the face–equals mucho cuteness.

5. Your lower 6 teeth (canines and incisors) are fused together into one protruding piece. This tooth “comb” is handy for grooming and applying your scent into your fur.

4. You are endowed with specialized grooming claws on your second toes, which help your tooth comb get the job done.

• FYI: the specialized toe claws are often called “toilet claws,” the word coming from a more traditional definition of toilet, meaning to groom yourself, not necessarily to…well, you know.

3. You get falsely accused of being too nosy because of your long snout.

2. Your lower jaw bones are divided into two parts joined together by cartilage at the center.  This means you can move your jaws with a little more flexibility than most primates with a single (fused) jawbone can, but your jaw is not quite as solid of a structure for muscles to attach.

• Fun fact! Since the top lip of a prosimian is anchored onto the gum, it is not pliable like a chimpanzee or other simian. Consequently, you won’t see the typical range of facial expressions involving the mouth in prosimians that you might find in monkeys and apes.

And, the number 1 way you know you’re a prosimian is……you give wet Eskimo kisses!!!

(Wild applause!)

So, there it is folks…Prosimians are different from other primates in that they tend to rely more on their sense of olfaction (smell) rather than visual cues (like we do) in their daily communication and travel through their environment. Prosimians exhibit more behaviors you might expect in non-primate mammals, such as leaving their infants in nests while they go out to find food, rather than carrying them on their backs.

Many primitive primates also have more than 2 nipples, and they generally produce litters of 3 or more young, rather than single infants as is seen in most other primates.  As far as their social systems, most scientists have not generally observed the complex hierarchies that exist in monkeys and apes in prosimian groups. This is probably because prosimians tend to be found in small family groups that are relatively isolated, rather than in large troops of individuals that overlap other groups.  Given that they tend to be loners, it seems that there is not as much need for prosimians to develop complex relationships with others.

These are generalizations, to be sure, as the prosimians are highly variable in the traits we have been describing.  One somewhat obvious example occurs with the Ring-tailed Lemurs that often give birth to single infants that they carry on their bellies and then backs until weaning.  Ring-tails are found in large groups, averaging 20-30 individuals, with even greater group sizes in some areas.  Given their large group sizes, there is a lot of interaction going on among individuals within the group. Some have even argued that the complexities of relationships among females in Ring-tail societies can rival that of some species of highly social monkeys. But, remembering that generalizations are just that (generally speaking but not always) prosimians are probably best described as the “primitive” members of the Primate Order, as they most resemble older, extinct primates of the past.

ANTHROPOIDS

Anthropoids include monkeys, apes, and humans. We all differ from prosimians because none of us has a tapetum for night vision or a wet nose, meaning that the outer part of your schnoz is covered by dry skin and small hairs. We tend to rely much more on our sense of sight for taking in our environment, and to help with that, we have color vision and an enlarged fovea of the eye, or the part responsible for sharp vision of small details. Our brain’s shape and the pattern of blood flow to our head are oriented in a particular fashion, and we have a fleshy upper lip fully capable of flapping in the wind when we stick our head out the window!

(A bit of learned advice: this type of activity is not recommended in parts of Texas where cattle trucks frequent the highway and are known for releasing periodic “showers” when you pass, nor in Southern Oklahoma where grasshoppers rise from the fields, pelting your vehicle at a rate of approximately 2 per second. In fact, while driving anywhere, it’s probably best to keep your face and body parts inside your vehicle at all times!)

Ok…moving on from that digression…Anthropoids also do not have tooth combs or grooming claws, like the prosimians, but do still participate in a wide variety of grooming behaviors that serve to strengthen social bonds.

Monkeys, apes, and humans all tend to be very social animals found living in large family units.  They are competitive but also cooperative and will be characterized by complex hierarchies, or ordering that dictates who will defer to whom in the group. The fact that anthropoids keep tabs on Who’s Who in their groups shouldn’t surprise you, given that most of the human cultures on this planet utilize some form of class system.  Usually, the higher up the chain you can climb for whatever reason, the more resources you tend to have…resources are things like food, space, mates, and grooming time. Compare Donald Trump and Joe the Plumber’s access to ladies, fine food, posh pads, and time spent lounging at the spa. Who has the higher status in terms of resources? Although perhaps of equal importance, who has the better pelage?

There are many interesting parallels between human and nonhuman primate societies, more of which are discussed in other sections of this website describing particular primate species.

An alternative classification to the term Anthropoid is to put monkeys, apes, and humans into the suborder Haplorrhini (Hap-loor-ee-nee), or the dry-nosed ones. This name has developed in part because of a tricky little primate known as a Tarsier. (Read more about tarsiers.) Tarsiers are hard to define as being prosimian or anthropoid because they share many of the prosimian features (unfused mandible, grooming claws, bicornate uterus, multiple nipples) but also have some of the traits that are unique to anthropoids, including the ones listed above (particular arrangement for blood supply to brain, dry nose, no tapetum, etc).  But, by using the terms Strephsirhini and Haplorhini, we now have groups based primarily on whether you have a wet nose or not.  Thus, we can keep all the non-tarsier, wet-nosed prosimians together and group the dry-nosed tarsiers, monkeys, apes, and humans together.

Remember that classification is an ever-changing field as scientists make new discoveries, both with genetics and the fossil record.  Even scientists that spend their whole lives working on the best way to group and classify primates probably will always have disagreements over how to organize all the information due to genuinely good arguments that can be used to support different points of view.