Primitive Dental Formula Anthropology Lab Report

University of Jigjiga Primitive Dental Formula Anthropology Lab Report

Introduction: The purpose of this lab is to acquaint you with some of the skeletal structures found in the order Primates. While this lab does not cover all of the variation found within primates, it will provide a general background to many of the structures used in investigating primate (including human) evolution.

Directions: Read the discussions of the different skeletal systems, and refer to the online specimens referenced to answer the questions. While there are a few right or wrong answers (e.g. correctly identifying teeth), the majority of the questions ask you to formulate your own interpretations/conclusions. For these types of questions there are no right or wrong answers. Instead, I ask you to support your conclusions in reference to the data that you collect from the specimens. Enter your responses directly into this word document and submit your completed lab to the Lab 1 submission folder on d2l (Assessments > Assignments > Lab 1).

Part 1 – Tooth Classes and Dental Formula. For this lab, you will evaluate specimens imaged at eSkeletons (http://eskeletons.org). Teeth provide useful information about the primate’s life, diet, and evolutionary relationships. They preserve information about development, nutrition, and general health. Their structures correspond with dietary preferences. They often correspond with genetic relatedness. Because teeth resist decay after death, they are often preserved in the fossil record. Below are some terms that you should learn.

Tooth Classes: Teeth are divided into 4 classes.

I = Incisors: bladelike or peg-like teeth at the front (anterior) of the jaw. Almost all primates have 8

incisors (4 upper and 4 lower).

C = Canines: cone-shaped or dagger-shaped teeth at front corners of jaws. Almost all primates have 4

canines (2 upper and 2 lower).

P = Premolars: teeth between canine and molars. The number of premolars in primates varies.

M = Molars: large, multicusped (having many bumps) teeth at rear of tooth row. Almost all primates

have 12 molars (6 upper and 6 lower).

To Do: Log onto eSkeletons (http://eskeletons.org), and view the human dentition. To do this, select “human” in the taxon list (top of page) or scroll over the images (top of page) to the human. Select the skull from the human skeleton, then select mandibular dentition and maxillary dentition to view the lower and upper dentitions, respectively. Look at the different views of the mandiblular and maxillary dentitions and use the tools (Teeth and Morphology) to learn about the different teeth and answer the following questions.

Questions: The eSkeletons project uses color coding to differentiate between tooth classes, when the “teeth” tool (for some specimens the “region” tool) is used. Using this tool to color code the human teeth, from the buccal, labial, and occlusal views, answer the following questions.

• How many lower (mandibular) Incisors (I) do humans have in one half of the jaw, and what color code is used in eSkeletons?
  • They have 2 on each side of the jaw.
• What color is used to highlight the lower canine?
  • Purple/pink
• How many premolars does the human have in one half of the mandible?
  • They have 2 premolars on each side.
• How many mandibular molars does the human have in one half of the jaw?
  • 3 mandibular molars on each side
• Looking at the upper (maxillary) teeth, how many incisors does the human have in one half of the maxilla?
  • 2 incisors on each side.
• How many canines does the human have in one half of the upper jaw?
  • 1 on each side.
• What color is used to highlight the upper premolars? How many upper premolars does the human have in one half of the upper jaw?
  • Violet
  • 2 on each side
• Which teeth are highlighted in green?
  • The molars

Additional Dental Terms:

Dentition – All teeth in the mouth (upper and lower)

Dental Arcade (arch) – All teeth in one jaw (either upper or lower)

Quadrant – ½ of an arch

Questions: Using the images (and tools) in eSkeletons (http://eskeletons.org), complete the following table by entering the genus name for each primate and recording the number of each tooth class in one quadrant of the upper dentition and one quadrant of the lower dentition. Note: You may have to look at different views (buccal, occlusal, labial) of each specimen to see labels for each tooth. The squirrel monkey specimen lacks the lower jaw, so only the upper teeth will be recorded for that specimen.

Dental Formula:

Anthropologists use a form of shorthand for recording the number of teeth a primate has. This is referred to as the dental formula and is a record of the number of teeth in one quadrant of the upper jaw and one quadrant of the lower jaw. For example, Humans typically have a total of 8 teeth in ½ of the upper jaw and 8 teeth in ½ of the lower jaw. In one quadrant of the upper jaw we have 2 upper incisors, 1 upper canine, 2 upper premolars, and 3 upper molars. In one quadrant of the lower jaw we have 2 lower incisors, 1 lower canine, 2 lower premolars, and 3 lower molars. This dental formula can be written as 2.1.2.3/2.1.2.3. The teeth to the left of the slash (/) are the upper teeth. Those to the right of the slash are lower teeth.

Questions: Refer to the table above (page 2) to answer the following questions.

• Record the dental formula for each primate.
• Which primates in the table have the same dental formula as the Chimpanzee?
  1. Baboon
• Do all primates have the same number of each tooth class in the upper and lower jaw?
  1. No
• What is unique about the lower teeth of the slow loris? Using lecture materials and your readings, can you identify what the dental feature at the front of the jaw is called? What might be the function of this feature?
• What is unique about the tarsier’s dental formula?
• There is a tendency in primate evolution for premolar teeth to be lost. The ancestral (primitive) primate had 4 premolars in each quadrant of the dentition, and premolar number has decreased from 4 to 3 to 2.
• Revisit eSkeletons (http://eskeletons.org), and look at the gibbon cranium and mandible. What is the dental formula for the gibbon?

Chimpanzee: 2.1.2.3/2.1.2.1

Baboon: 1.2.3/2.1.2.1

Squirrel Monkey: 1.1.3.3

Common Marmoset: 2.1.3.2/2.1.3.2

Tarsier: 1.1.3.3/1.1.3.3

Slow Loris: 1.1.2.3/1.1.3.3

Which primates are more primitive with regard to upper premolar number?

Which primates are more derived with regard to upper premolar number?

Part 2 – Teeth and Diet

A primate’s teeth are responsible for breaking down food items into smaller pieces that can be more easily digested by the intestines. Thus, the shape of teeth corresponds with dietary preference.

Questions: Visit eSkeletons (http://eskeletons.org) and compare the dentitions of the orangutan (a fruit eating primate), the gorilla (a leaf and vegetation eating primate), and the tarsier (an insect eating primate).

Examine the teeth of these three primates and answer the following questions about molar structure and diet.

• Which molar teeth have more rounded cusps (bumps) on them? Which are pointier? How might these differences relate to diet?
• Which molar teeth have longer crests on them (crests are the ridges of enamel that run between cusps)? Which have shorter crests? How might these differences relate to diet?
• Which primates have molars that are better for puncturing, crushing, or slicing/shearing?
• 4)Look at the specimens figured below. What do you think this primate eats? What characteristics of the dentition leads you to this conclusion? Note: the scale bars = 1 mm.

Premolars are pointer. Molars have more bumps

Molars have longer crests and premolars have shorter crests.

Puncturing: tarsier

Crushing: gorilla

Shearing: orangutan

Fruits and insects

Part 3 – Cranium. The primate cranium is responsible for housing the brain and the major sense organs (e.g. eyes, nose, ears, tongue). Learn the following terms, then answer the following questions about the crania provided.

Orbit = eye socket

Postorbital bar = bar of bone that surrounds the eye socket

Postorbital closure = eye socket is closed off with bone from behind

Browridges = ridges of bone above the eye sockets

Prognathism (prognathic) = face projecting forward (elongated snout)

Orthognathism (orthognathic) = flat face – not projecting forward

Sagittal crest = ridge of bone running down the center of the skull from front to back

Post-orbital constriction = bone pinches inward behind orbits when viewed from above

Questions: Refer to the specimens presented in eSkeletons (http://eskeletons.org) to compare the crania of a strepsirrhine primate (ruffed lemur), a New World monkey (squirrel monkey), an Old World monkey (baboon), an ape (gorilla), a human, and a non-primate (coyote; pictured below). Record the following information for each specimen relative to the others.

Canis latrans (coyote)

• Do the orbits face more forward or to the side?
• Is there a postorbital bar? Is there postorbital closure?
• Are there brow ridges present, and how big are they?
• Is there a sagittal crest?
• Is there postorbital constriction?
• How big is the braincase relative to the face?
• Based on the following traits, which primates do you think are most similar to each other?

Ruffed Lemur:

Squirrel Monkey:

Baboon:

Gorilla:

Human:

Coyote:

Ruffed Lemur:

Squirrel Monkey:

Baboon:

Gorilla:

Human:

Coyote:

Ruffed Lemur:

Squirrel Monkey:

Baboon:

Gorilla:

Human:

Coyote:

Ruffed Lemur:

Squirrel Monkey:

Baboon:

Gorilla:

Human:

Coyote:

Ruffed Lemur:

Squirrel Monkey:

Baboon:

Gorilla:

Human:

Coyote:

Ruffed Lemur:

Squirrel Monkey:

Baboon:

Gorilla:

Human:

Coyote:

Post orbital closure:

Relative brain size (size of the braincase relative to the face):

Orbit position/orientation:

Part 4 – Postcranial skeleton. In this section, we will focus on parts of the hind limb (leg) that are related to bipedalism (habitual walking on 2 legs) – the os coxa (coxal bone of the pelvis) and the femur (thigh bone).

Questions: Refer to the diagram (below) and the baboon, chimpanzee, and human specimens of the os coxa and femur on eSkeletons (http://eskeletons.org) to answer the following questions. Note: To access the os coxa and femur for each primate, select the leg region from the skeleton image. Be sure to look at the bones from different angles. The “morphology” link above each bone image will aid in describing what you see.

• 1)Generally speaking, which species (baboon, chimpanzee, or human) has more robust (heavily built) bones?
• 2)Describe the shape of the os coxa (ilium, ischium, and pubis) of each species. How are they similar? How do they differ?
• 3)Compare the femur head (the ball that articulates with the pelvis) of each species. What are the similarities and differences?
• 4)What are the differences in the shape of the human knee, the chimp knee, and the baboon knee (refer to the end of the femur that is furthest from the head/hip)?