2100 anthropology exam.

ATH 2100L LAB 6: READING

DIRECTIONS: Please read the materials that follow and then complete the Lab 6 Quiz on PILOT.

By the time you finish reading these materials, you should be able to answer the following questions about primate taxonomy and anatomy:

1. What anatomical traits define each of the taxonomic groups within the Order Primates?

2. What are the different types of primate locomotion and their skeletal characteristics?

3. What is the intermembral index?

The living primates: taxonomic classification

Though you may not have known this before enrolling in ATH 2100, humans are primates. In fact, the Order Primates (pronounced Primate-ees) includes humans, apes, monkeys, tarsiers, and prosimians. You are mostly likely familiar with humans, apes, and monkeys but you probably have never heard of the group known as the prosimians. In the past (i.e., when I took this class in college), all primates belonged to one of two larger taxon: Prosimians or Anthropoids.

Tarsiers along with lemurs, lorises, and galagos (now called Strepsirhines) were known as the Prosimians because they were nocturnal and generally small-bodied primates. Today we know that despite these similarities, tarsiers are more genetically similar to Haplorhines (previously known as the Anthropoids). Below is a table showing the old and new terms. Notice that the tarsiers move from Prosimian to Haplorhine:

The suborder Haplorhine comprises the majority of primate species alive today. Haplorhines can be further subdivided into Platyrrhines (aka New World Monkeys) and Catarrhines. The Catarrhines can be subdivided into Cercopithecoids (aka Old World Monkeys) and Hominoids. Cercopithecoids can further be broken into the Cercopithecines (aka cheek pouch monkeys) and Colobines (aka leaf eating monkeys), while hominoids include humans, greater apes, and lesser apes.

Defining anatomical characteristics

Below is a list of the defining characteristics of each primate group noted above. Where appropriate, cranial features are highlighted in blue.

ALL PRIMATES: There are many defining characteristics of primates. From a cranial perspective, the strongest defining features are more forward facing eyes and the presence of a post-orbital bar. The post-orbital bar is a rim of bone on the outside of the eye socket (and can be seen in some other animals). In Haplorhines, this bar is also attached to a plate of bone behind the eye. We call this post-orbital closure. Please check out the image to the right or here: http://animaldiversity.ummz.umich.edu/collections/contributors/anatomical_images/family_pages/primates/primates//medium.jpg

STREPSIRHINE (Lemurs, lorises, galagos): Defined by the presence of a moist rhinarium (for smelling scents, kind of like a dog), a dental comb (for grooming; see image below), and a long toilet or grooming claw (also for grooming). Unlike most other primate groups, strepsirhines are heavily reliant on their sense of smell. Therefore, most strepsirhines also have a long snout to accommodate olfactory nerves.

For a larger image, visit:

http://upload.wikimedia.org/wikipedia/commons/thumb/4/45/Lemur_catta_toothcomb.jpg/220px-Lemur_catta_toothcomb.jpg

HAPLORHINE (Tarsiers, apes, monkeys, humans): defined by the presence of a dry rhinarium (because vision is more important than smell) as well as the absence of a dental comb and the absence of a toilet claw.

TARSIERS: despite some similarities between tarsiers and the Strepsirhines, the defining difference between tarsiers and all other groups is the presence of a structure called the lateral genticulate nucleus in their brains. This structure contributes to a tarsier’s heightened sense of vision as they search for food in the dark. No tarsier skulls will be explored in this lab.

PLATYRRHINES (New World monkeys): the name of these monkeys reveals much about their facial characteristics. “Platy” means “flat” and “rhine” refers to the nose (like rhinarium). As such these monkeys are defined by their broad, flat noses and outward facing nostrils (i.e. wide septum). These monkeys are also defined by the presence of a prehensile (grasping) tail and 2:1:3:3 dental formula.

CATARRHINES (Old World monkeys and apes): this group, which includes the cercopithecoids and hominoids, is defined by downward facing nostrils, the presence of a narrow septum, and a 2:1:2:3 dental formula.

(a)

(b)

A comparison of the dental formulae and nasal septums of

(a) Catarrhines and (b) Platyrrhines.

CERCOPITHECOIDS (Old World monkeys): these monkeys also have tails, like New World monkeys but they are not designed for grasping and instead help these monkeys with balance. Dentally, the Old World monkeys exhibit a unique molar pattern called bilophodont molars. Note in the image to the right how there appears to be a line dividing the tooth into two halves (one on top, one on bottom). Each of those halves then has two cusps each (four cusps total). In general, bilophodont molars are symmetrically shaped and are useful for grinding foods.

HOMINOIDS: this last taxonomic grouping includes all apes and humans. Unlike the monkeys, tarsiers, and strepsirhines (who all have tails), hominoids are tail-less. Dentally, the hominoids exhibit a unique mandibular (lower jaw) pattern called the Y-5 pattern. As illustrated in the image to the right, these lower jaw molars have five (not four) cusps, which are arranged in a “Y-shape.”

Locomotor patterns

Compared to other mammalian groups, primates have a number of different locomotor patterns (i.e., ways of getting around). When only skeletal elements remain, it is useful to calculate the intermembral index to learn more about a particular “mystery primate’s” potential locomotive patterns. The intermembral index is simply the proportion of arm to leg length.

Below is a list of the locomotor patterns (and their associated skeletal characteristics) used by different primates today as well as links to videos showing these different types of locomotion.

QUADRUPEDALISM: All primates except humans walk on all fours (i.e., quadrupedally). There are variations on this type of walking, some of which are highlighted below:

a) Arboreal quadrupedalism: This is a common type of locomotion that involves movement on top of tree branches. Arboreal quadrupeds tend to have short limbs that are equal in length, long tails for balance, and a low center of gravity.

b) Terrestrial quadrupedalism: This type of locomotion occurs on the ground. Terrestrial quadrupeds have long limbs (to increase stride length) and some species even have shortened tails.

i) Knuckle-walking: This is a form of terrestrial quadrupedalism found among gorillas and chimps which involves walking on the tips of the knuckles. Their long, curved fingers are adaptations for gripping branches, but they also move on the ground so they have to tuck in their fingers! If you look closely in this video, you can see knuckle-walking in action: http://www.youtube.com/watch?v=2Npc5QlS6Iw

d) Vertical clinging and leaping (VCL): This type of locomotion is used by tarsiers and some strepsirhines and haplorhines (New World monkeys). Usually VCLs have very long legs (for propulsion) and shorter arms. Some VCLs like tarsiers have elongated tarsal (ankle) bones. A VCL primate crouches with a bent leg and leaps from one tree to the next. http://www.youtube.com/watch?v=eGZdBi_dT-s

e) Suspensory/Brachiation: This type of locomotion uses the arms to support the entire body below a tree branch. Suspensory primates usually have very long arms, short legs, and long, curved fingers to aid in gripping. http://www.youtube.com/watch?v=H3Wk33FZiVw

BIPEDALISM: Humans always walk on two legs and some primates (especially chimps and bonobos) will occasionally walk bipedally, as needed. Human bipedalism is called habitual bipedalism while the occasional bipedalism of other primates is called facultative bipedalism.

Here’s a brief summary of the key skeletal characteristics for each locomotion type.

Please note, you are not required to bring a copy of this reading to lab, but you are encouraged to do so in case you need to reference the materials as you answer lab questions. If you want to avoid large stacks of paper and the cost of printing, consider arranging a rotation among lab group members for printing and bringing copies to each lab.