12 Primate Characteristics

In the previous lecture we looked at mammals more generally. Now we're going to focus on the order of primates.

Primate evolution refers to how anatomical and behavioral traits evolved as adaptations to particular environmental circumstances.

Here, the environmental circumstances that we're looking at is arboreal living or living in trees. And so in order to understand how primates came to live in trees, we, we have to look at their adaptation in relation to climate, diet, habitat and predation.

Adaptation toward arboreal living or living in trees includes behaviors such as living in social groups.

There are a few primates that are solitary, but the majority of primates live in social groups.

Next is omnivorous diet. This the ability to eat both plant and animal protein. And last is visual predation.

So using relying on sight as the primary sense to hunt.

Specialized traits that make visual predation possible are

prehensile hands and feet. So the ability to grab with both your hands and your feet,

two front facing eyes, and fine visual and tactile discrimination. There are three hypotheses that try to explain how primates came to live in trees.

The first hypothesis is the arboreal hypothesis, the idea that primates increasingly found food in trees

and therefore developed an increased reliance on vision and prehensile hands and feet as an adaptation to arboreal living.

In other words, we developed these traits as we moved further and further up the tree canopy to look for food.

The second hypothesis is the visual predation hypothesis. And it's the

idea that early primates may have first adapted to shrubby forest undergrowth and Li Loew's tear of the forest canopy where they hunted insects and smaller prey.

It's the idea that primates developed prehensile hands and feet, front facing eyes, and fine visual and tactile discrimination on the forest floor first.

And as food ran out in the forest floor and they had to move higher and higher up the tree canopy, they brought these adaptations already developed in tow with them.

The last hypothesis is the flowering plants hypothesis. It's the idea that these basic primate traits, prehensile hands and feet, two front facing eyes, fine visual and tactile discrimination, developed along with the appearance and diversification of flowering plants about 140 million years ago.

And so, front facing eyes, grasping hands, and fine visual and tactile discrimination, were needed for feeding on fruits, berries and seeds.

And so if you think about your own trips to the grocery stores and you're trying to pick out fruit, and you're trying to find fruit that is ready to eat, that is ripe and good to eat, how do you discern what is good to eat and what is not to

and what is not good to eat. You definitely smell it, but you also feel it, and the right texture will tell you if it is ready to eat.

This fine visual and tactile discrimination is not only important for discerning what is edible and not edible, it's also helpful for discerning what is poisonous and not poisonous.

Not one of these hypotheses is more correct than the other, and in fact, the reality might be that it is a combination of all three.

So these hypotheses are not mutually exclusive.

Let's move on to primate characteristics.

So, in general, primates share all of these traits. All primates have body hair.

We are placental mammals, and therefore we have long gestation or pregnancy periods. All primates are heterodonts, meaning that we have a variety of canines, incisors, premolars and molars.

We are also all endothermic, meaning that we are all warm blooded and can regulate our own internal body temperature.

And compared with other species, primates have larger brain sizes. The four categories of primate characteristics that we're going to explore in this lecture are limbs and locomotion, diet and teeth,

senses and the brain. And last, we are going to look at maturation, learning and behaviors.

We're going to look at all these categories as responses to environmental challenges, being social and arboreal animals.

First, we'll look at limbs and locomotion.

In general, primates have prehensile hands and feet.

We have five digits on both our hands and our feet.

Primates have opposable thumbs and a divergent toe. The divergent toe is the opposable thumb. But on the foot, primates in general also have nails.

And on the back of our nails, we have tactile pads that are enriched with sensory nerve fibers at the end of our digits.

Here we have a comparison between a chimpanzee foot and a human foot. Chimpanzees have a divergent toe.

The human foot does not. Right. We do not have

a thumb that is opposable on our foot.

The chimpanzee foot is your ancestral trait.

The human foot is your derived trait. That is the modification of the ancestral trait. The chimpanzee foot is also generalized.

And so chimpanzees can get around using a variety of locomotion. They can walk, they can climb, they can crawl.

The human foot is specialized, meaning that we can only really get around by walking bipedally.

And so pendactyly is your ancestral trait.

All of these Images are derived traits, and so horses,

their hooves are derived traits. These derived traits are also highly specialized. A horse's hoof is very good at walking, running and absorbing shock.

It is not so good at climbing trees.

In terms of locomotion, all primates, except for human beings, are quadrupedal. Human beings are the only primates that are full time bipeds, quadrupedal, meaning that they move around using all four limbs.

Different forms of quadrupedal locomotion include vertebrae, vertical clinging and leaping brachiation.

Semibrechiation refers to a combination of vertical clinging and leaping with brachiation. And last is knuckle walking.

We're going to go over each of these forms of locomotion one by one.

Tarsiers are a good example of vertical clinging and leaping. Tarsiers are called tarsiers because they have these very well developed metatarsal or finger and toe bones.

They also have very strong quads. And so the way that tarsiers move around is that they hang on to a tree or to a branch, so they're vertically clinging and then they'll use their powerful hind legs to project themselves onto the next branch.

And so they leap. They vertically cling and then they leap.

Brachiation refers to swinging from branch to branch. And so examples of brachiators would be gibbons.

Gibbons have specialized shoulder girdles that allow them to suspend from branches with very little effort.

Last is knuckle walking. Examples of knuckle walkers would be chimpanzees and gorillas. You'll see that they swing and then they settle.

They settle. The full weight of their body is not on their palms but on their knuckles.

Next is diet and teeth.

Primates lack a dietary specialization, meaning that we are not just full time herbivores or full time carnivores, but we are omnivores.

We are able to eat both plant and animal protein. And so our omnivorous diet can include fruits, nuts, seeds, leaves and other plant materials, but also animal proteins such as birds, amphibians and other small mammals.

Because we have this omnivorous diet, we are heterodonts, meaning that

we have a combination of incisors and canines which are very good at cutting and tearing meat. And we also have molars and premolars, which, with these low rounded cusps that are good at tearing and grinding meat.

If you remember to our previous lecture, we talked about homodonts such as crocodiles and elephants,

and so crocodiles only have incisors and so they have these high pointed cusps. That are really good at tearing meat, but not very good at chewing.

The other homodont that we talked about were elephants. And so they have these very flat, low molars.

And elephants with these low, flat cusps are really good at grinding plant material, but they're not really good at tearing off pieces of meat.

Primates, on the other hand, have this molar shape that is in between a crocodile and elephant, right?

So our molars have these low, rounded cusps that are good for grinding, but also good at cutting and tearing apart meat as well.

The dental formula refers to the number of teeth.

The dental formula refers to the variety of teeth within our mouths and the number of these varieties.

And so the way that we're going to calculate our dental formula is that we're looking at one quadrant.

And so in our mouths, we have your upper jaw and your lower jaw,

your upper jaw and your lower jaw have the same number of teeth and the same variety of teeth. And so to calculate our dental formula, we are only looking at 1 quadrant or 14 of our job.

And so within this quadrant, for humans, we have

two incisors, one canine, two premolars and three molars. So we have two, one, two, three

on our upper jaw,

and we have two, one, two,. Three in our lower jaw, right? So two incisors, one canine and

two premolars, three molars. With new World monkeys, it is slightly different. New World monkeys, on the other hand, have two incisors, one canine, three premolars, and three molars.

And so the big difference between humans, apes, and Old World monkeys

versus New World monkeys is that New World monkeys have one extra premolar.

Last, we're going to talk about cognitive adaptations for arboreal living and hunting in senses and the brain.

And so, in general, primates are diurnal, meaning that they conduct most of their activities

the daytime, including hunting. And because,

And because we are diurnal, most primates have color vision. There are certain primates that are nocturnal,

and those primates do not have fully developed color vision.

Primates also have depth perception. This is thanks to our two front facing eyes. Our two front facing eyes creates an overlapping field of vision, also known as stereoscopic or binocular vision, that allows us to see

different depths. This is extremely important when you're moving from branch to branch. Having depth perception allows you to know what, where that next branch is.

If you miscalculate, you could plummet to your death. And so binocular vision is very important for living in trees and especially for hunting in trees.

Here we have Two skulls. We have the skull of a male baboon

and we have the skull of a wolf.

This is a great example of a false similarity or an analogous trait. They look quite similar, but these similarities are false.

If we look at the baboon skull,

he has two front facing eyes. The reason why his snout is long and looks like the wolf's snout is not because he relies on smell to hunt like the wolf.

The reason why he has a long snout is because he has these very large canines. And the long snout is to accommodate these canines.

Make no mistake, baboons hunt using vision as their primary sense. You'll also see in primate brains the expansion and increased complexity of the neocortex.

Primate brains in general are much larger in size than other species, and our neocortex is also much larger in size.

And the neocortex is important because that is where the different sensory modalities are combined. So information from your five senses are processed in your neocortex in terms of maturation, learning and behavior.

Primates have a much longer gestation period, which allows for slow growth and development. We also have reduced number of offspring, so single births are the norm.

There are some primates that give birth to twins as the norm, but for the most part, primates give birth to only one child or one offspring at a time, and this allows for increased parental investment.

Primates are also characterized by delayed maturation or longer periods of infancy and adolescence, where they are dependent on at least one parent.

Having a longer childhood allows primates to have more opportunities to learn from their parents and from their peers.

And last, primates tend to live in social groups, and there's usually a permanent association of adult males with the group.

So the general trend is that when females reach sexual maturity, they will leave the group and join another social group.

Males, however, tend to stay in the same social group throughout their lives.

So having this long childhood period and living in social groups allows primates more opportunities to learn from each other, and that is what makes primates the more intelligent order.