How do haplorhines differ from strepsirhines

ASM 104

Fall 2012 Name: __________________________

Lab 7: Primate Classification

Objectives

After this lab you should be able to do the following, using evidence from the skeleton:

· Distinguish between primates and non-primates

· Distinguish between strepsirhines and haplorhines

· Distinguish between tarsiers and anthropoids

· Distinguish between platyrrhines and catarrhines

· Distinguish between hominoids and cercopithecoids

Background

Primates are a very diverse group of animals. However, they all possess some traits that differentiate them from other mammals. Among these traits are those that relate to grasping with the hands and feet, an increased reliance on vision, a decreased reliance on the sense of smell, and traits related to greater development of the brain.

Additionally, there are many traits that differ among the major groups of primates. These traits include those related to the skeletal anatomy of the eye orbits, the number and types of teeth, and traits that relate to specific forms of locomotion.

The following cladogram illustrates the different groups of primates and the relationships between them. Refer to it as you proceed with the lab in order to understand the way biological anthropologists organize and classify primates. There is also a similar diagram on the last page.

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Part 1. Learning the traits

Station 1. Cranial Traits

A. Postorbital bar and postorbital closure

A postorbital bar is a bony ring that forms the outside border of the eye orbit. This structure encircles the eye orbit but does not form a wall behind the orbit. This structure is found in all primates. Primates that have a postorbital bar as well as a complete bony wall behind the orbit (i.e., a fully enclosed orbit) have postorbital closure. Strepsirhines have a postorbital bar, but not postorbital closure. Haplorhines (except tarsiers) have postorbital closure. Tarsiers have partial postorbital closure (you can see this on the tarsier skull in Station 6).

1. Which of the specimens at this station has only a postorbital bar? Which has postorbital closure?

Postorbital bar ONLY _________

Postorbital closure ________

Station 2. Teeth

A. Dental formula

A dental formula states the number of each type of tooth (incisor, canine, premolar, and molar) in a quadrant of the mouth. The formula is written with the numbers corresponding to one quadrant of the upper jaw on top and the numbers corresponding to one quadrant of the lower jaw on the bottom. For example, the human dental formula is 2.1.2.3/2.1.2.3

1. Write the dental formula for each of the mandibles at this station:

Specimen A –

Specimen B –

Specimen C –

B. Bilophodont molars

Bilophodont molars are molars that possess two ridges, or lophs. This lophs run from the tongue-side of the tooth to the cheek-side, and thus there is one ridge on the anterior, or front, aspect of the tooth and one on the posterior, or back, aspect. Cercopithecoids are the only primates that possess this trait.

2. Looking at the mandibles at this station, which specimen has bilophodont molars?

Station 3. Tooth comb

Strepsirhines have mandibular incisors that are modified to be long and thin, like the tines on a comb. These incisors are procumbent, meaning they stick straight out. Strepsirhines use their lower incisors to groom themselves and each other. This is a shared, derived trait that defines this clade. Their upper incisors are correspondingly small. Haplorhines do not use their incisors to groom, and their lower incisors are never as procumbent as in strepsirhines.

1. Which of the specimens has a tooth comb?

Part 2. Distinguishing taxa

Use the information presented in lecture to answer the following questions at Stations 4 through 8.

Station 4. Is it a primate?

1. Look at the skeleton. To determine if it is a primate or not, you can look at the orbits, and the phalanges.

Is it a primate? ________________ Why or why not? _______________________

Station 5. Is it a strepsirhine or a haplorhine?

The Primate Order is divided into two suborders: Strepsirhines and Haplorhines. There are two obvious cranial differences between the members of these suborders.

Which suborder has only a postorbital bar (not postorbital closure)?

Which suborder has a tooth comb?

Use your answers to the above questions to determine the classification of the skulls at this station. Indicate whether you think the skull is a strepsirhine or a haplorhine.

Skull A _____________________________

Skull B_____________________________

Station 6. Tarsiers: how to classify

Tarsiers have caused a lot of confusion for biological anthropologists because they share many traits with other haplorhines (the anthropoids: monkeys, apes, and humans), but they also share ancestral traits with strepsirhines. This fact has made tarsiers difficult to classify.

1. Examine the tarsier mandible. Does it have a tooth comb? (Remember, this is a shared, derived trait that defines strepsirhines)

2. Examine the tarsier skull at this station, and compare the degree of postorbital closure with the hominoid skull. Which skull has only partial postorbital closure?

3. Examine the photos of the real tarsier mandible. Does it have a fused or unfused mandibular symphysis?

4. Anthropoid primates have a fused mandibular symphysis and complete postorbital closure. Is the tarsier an anthropoid?

Station 7. Is it a platyrrhine or a catarrhine?

The dental formula is the easiest way to determine whether an anthropoid skull is a platyrrhine or a catarrhine.

1. Using your notes from lecture, write the entire dental formula (both maxilla and mandible) for:

Platyrrhines: Catarrhines:

2. Using dental formula, identify whether the skulls at this station are platyrrhines and catarrhines.

Skull A________________________

Skull B_________________________

Station 8. Is it a hominoid?

Catarrhines are divided into two groups: cercopithecoids (Old World monkeys) and hominoids (apes). Cercopithecoids are defined by having bilophodont molars.

A. If you have a skull that you know is a catarrhine based on dental formula, you can determine if it is a cercopithecoid or a hominoid by looking for bilophodont molars.

1. Examine the two skulls at this station and write your classification of either cercopithecoid or hominoid on the line provided.

Skull A ______________________

Skull B ______________________

B. If you have a skeleton, then you can look at other features. Hominoids are mainly defined on the basis of their postcranial skeleton, because of their suspensory locomotor behavior.

2. Look at the pictures of skeletons at this station and fill in the chart below.

Chest width (broad side to side or deep anterior to posterior?)

Tail

(yes or no?)

Length of limbs (longer arms or equal limbs?)

Picture A

Picture B

3. Which picture is of the hominoid? Use the information from lecture and in the above chart to answer this question.

Part 3. Identifying primate taxa

Success! This summer you discovered two fossil primates that were previously unknown. Now it is time to identify the primates you found. Examine your primate skulls for primitive and derived features and answer the following questions. Features you should examine are those you have assessed above. These are the keys to figuring what kind of fossils you have.

Station 9. Specimen 1

This primate fossil was found at the site in Egypt where many important Oligocene fossil primates have been found.

1. What is the name of this site?___________________________

2. Is the primate a strepsirhine or a haplorhine? List at least two features that support your answer.

3. Is it a platyrrhine or catarrhine? List one feature that supports your answer.

Specimen 2

4. Is this specimen a catarrhine or a platyrrhine? Why?

5. Is this specimen a cercopithecoid or a hominoid? Why?

Part 4. Summary and Review

A. Primate Origins. Match the hypothesis with its description:

A. Arboreal Living Hypothesis B. Visual Predation Hypothesis

______ Stereoscopic vision and grasping hands were selected for as primates evolved into insectivores living in the underbrush

_______ Grasping hands, stereoscopic vision, and intelligence were selected for as primates evolved into tree-dwelling animals

B. The diagram on the next page shows one way the Primate order is classified. You can use this to study from! Fill in defining traits that you have learned in this lab at the numbered positions on this diagram. Feel free to include more than what has been asked for.

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Non-primate mammals

Platyrrhines

Tarsiers

CATARRHINES

Lorises

Hominoids

HAPLORHINES

Cercopithecoids

Lemurs

STREPSIRHINES

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