Clark Larsen Answers Students FAQs

1. Question: What are the traits that are unique to primates and enable them to be well-suited to an arboreal environment?

Response: Primates have a unique suite of characteristics that enable them to be ideally suited to life in the trees. Primates have a very flexible, versatile skeletal structure that allows a wide range of motions and numerous types of locomotion. The primate hands and feet are prehensile with opposable thumbs and big toes that enable them to grasp tree branches. Humans, however, do not have the opposable big toe or prehensile foot due to our bipedalism. The vertebral column of primates has five different types that gives the body greater flexibility in movement. Primates also have enhanced reliance on vision, reflected in the forward-facing eyes, overlapping field of vision, and color vision. Primates have enhanced sense of touch, with nails instead of claws and dermal ridges, which provide grip. Lastly, primates rely less on smell and hearing, reflected in the absent rhinarium and reduced snout length.

See Figure 6.2 Primate Adaptation in Microcosm, part 1

See Figure 6.2 Primate Adaptation in Microcosm, part 2


2. Question: What are the two major classes of primates and what sets the two groups apart?

Response: The two major groups of primates are the prosimians, or lesser primates, and the anthropoids, or higher primates. Prosimians retain a variety of primitive features, such as a rhinarium and an olfactory bulb. In addition, they often retain claws and their fingers are less dexterous than other primates. Prosimians have more specialized diets than other primates and are nocturnal. They also possess some derived features, such as the dental comb. The major primates within the prosimians are the lorises, lemurs, tarsiers, and galagos. Anthropoids possess numerous derived traits, including a larger brain, more sexual dimorphism in body size, fewer teeth, and nails instead of claws. They have also lost the rhinarium and developed color vision, both of which reflect their increased reliance on vision. Anthropoids tend to be more omnivorous and the majority of them are diurnal. Anthropoids include New World monkeys, Old World monkeys, apes, and humans.

See Figure 6.18 Order Primates, part 1

See Figure 6.18 Order Primates, part 2


3. Question: What are the key factors that determine a female primate’s success in feeding?

Response: Female primate success in feeding is related to the quality, distribution, and availability of food. The quality of food reflects the amount of energy provided and the ease with which the food can be digested. Fruit, for example, is very easy to digest and contains sugar, an energy-rich food. Mature leaves, on the other hand, are hard to digest and provide little energy. The location or distribution of the food reflects the amount of energy the female has to expend to collect food. If food is abundant and found throughout the forest, like leaves, she will have to use very little energy in gathering food. If, however, the food is sparse and widely distributed, like fruit, she will need to use lots of energy to acquire the food. The availability of food reflects seasonality and rainfall. Foods, such as fruit, are only available at certain times of the year, while leaves are typically available year-round. The female must balance these key factors by acquiring as much energy as possible while expending as little energy as possible.


4. Question: How do male and female primates differ in their reproductive strategies?

Response: Males engage in competition for access to females through physical altercations as well as vocalizations and displays. Since females are choosing their mates, sexual selection of male traits occurs. For example, the large body size and large canine size in males is the result of females preferentially mating with males who have larger body size and canines. Males also practice infanticide, which causes the females to resume ovulation, allowing the new male to impregnate her. Females, on the other hand, do not compete for access to males. Instead, they compete for access to food resources for themselves and their offspring. Most typically, females of higher rank have greater access to resources than females of lower rank. This greater access to food often results in more offspring as well.


5. Question: How do platyrrhines and catarrhines differ?

Response: Platyrrhines and catarrhines differ in three main areas: dental formula, prehensile tails, and nasal shape. First, platyrrhines have six upper and six lower premolars, while catarrhines have four upper and four lower premolars. The prehensile tail is only found in platyrrhines; no catarrhine has this feature. While not all platyrrhines have prehensile tails, this feature is only found New World Monkeys. Lastly, platyrrhines have wide, flat noses with a wide septum and outward pointing nostrils. Catarrhines have narrow noses with a narrow septum and downward pointing nostrils.

See Figure 6.22 Platyrrhines vs. Catarrhines