Comparative Osteology

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Activity: Cranial Comparison

Topic: Comparative Osteology

Physical anthropologists rely on osteology, or the scientific study of bones, to identify individual species, learn about the lives of an individual, or even to identify ancient illnesses (aka paleopathology). The skeletal features of bones reflect the life histories of individuals, and trained osteologists can use those features to identify the age, sex, diet, and, at times, even the cause of death of a particular specimen.

However, analyzing and comparing the bones from different species can also tell us about the evolutionary history of those species and the degree to which different species are related. For example, the overall organization of dog skeletons would be very similar to those of wolves. The same could be said for different species of fish, reptiles, turtles, etc.

In anthropology, osteologists often compare human skeletons with those of other primates so that we can learn about our ancient human past. In today’s activity, we will compare cranial features of human, chimpanzees, and coyotes, to learn about cranial capacity, dental formulas, diet, and the overall degree of similarity among species. For this activity, think about the similarities and differences between each of the individual specimens. If they are similar, what makes them similar? If they are different, then how could we explain those differences in an evolutionary context?

Discussion:

Why would humans share so many features with primates, but not with the coyote? Does that reflect out shared evolutionary past?

What other species would a coyote be similar to?

Consider the size, shape, and overall dentition of the species analyzed here. Is it possible to infer the diet of a specimen based on dentition?

-Can you tell if an individual is an omnivore, carnivore, or herbivore?

-Ask students to describe the diet of humans, chimpanzees, and coyotes based on their dentition.

Ask students to discuss the implication of cranial capacity.

-bigger brain (generally) means increased intelligence.

-Some big-bodied animals have larger brains, but we have a massive cranial capacity relative to our body size. That would suggest that our evolutionary ancestors evolved to prioritize intelligence.

 Materials:

1 human skull, 1 coyote skull, 1 chimpanzee skull per group.

Also 1 unknown skull, to be discussed as a class.

 COMPARATIVE OSTEOLOGY:

Humans, Primates, and Mammals

 Features of the Skull

 Compare the drawings below with the three skulls that you have been provided.

Label one of the skulls below as human and the other as chimpanzee

What features did you use to identify which skull was human and which was chimpanzee?

Comparing Dentition

 A dental formula represents the number of different types of teeth for a particular species.

The dental formula is written like a fraction, with four numbers on top and four on the bottom. Each number represents the number of each type of teeth, beginning with Incisors, Canines, Premolars, and Molars.

Incisors: shovel-shaped teeth located in the front of the mouth.

Canine teeth: sharp, pointed, and conical, teeth located behind the incisors.

Premolars: Teeth located between the canines and molars used to hold prey, assist in cutting and/or grinding

Molars: The rear grinding/shearing teeth located posterior to the premolar

Look at the crania in your collection and count the total number of teeth for each species.

How many teeth does the human skull have?                   ___________________

How many teeth does the chimpanzee skull have?           ___________________

How many teeth does the coyote skull have?                    ___________________

Which crania are more similar based on the total number of teeth?

___________________________________________________________________________________________________

 

  1. Count the different types of teeth for each skull:

Upper Jaw:                                         Human          Chimpanzee             Coyote

    1. Incisors:                     ___________           ___________               ___________
    2. Canines:                      ___________           ___________               ___________
    3. Premolars:                 ___________           ___________               ___________
    4. Molars:                       ___________           ___________               ___________

Lower Jaw:                                         Human          Chimpanzee             Coyote

  1. Incisors:                     ___________           ___________               ___________
  2. Canines:                      ___________           ___________               ___________
  3. Premolars:                 ___________           ___________               ___________
  4. Molars:                       ___________           ___________              ___________
  1. Of the human, chimpanzee, and coyote skulls, which are more similar?

Cranial Capacity

The brain is located inside the cranium. The internal volume of the cranium is called cranial capacity.

 

(Humans)                         (Chimpanzees)                  (Evolutionary Ancestor)

 

  1. Of the human, chimpanzee, and coyote skull, which has the largest cranial capacity?

_________________________________________________________________________________________________

  1. What do you think cranial capacity reflects?

_________________________________________________________________________________________________

 

_________________________________________________________________________________________________

 

_________________________________________________________________________________________________

 

Week 10: Human Osteology

Hello all!

Last week we introduced the students to osteology. This week we brought some more bone castes and taught the students about human osteology. We focused on the process of sexing skeletons. Physical anthropologists can tell many things from studying a human skeleton. One of the easier things to determine is the biological sex of the person.

Before starting the activity, we showed the students some of these features using the castes. For each group we provided both a female and male skull as well as female and male pelvises due to the fact that these are the most useful for determining the sex of skeletons. We showed the students that male pelvises have part of a bone that bends forward whereas a female does not. This bone, called the sacrum, is more straight in women so that is does not act as an obstruction during childbirth. We also showed the students that male skulls have a tendency to be more robust and less smooth than female skulls.

skeletonpictures
Right to Left: male skull, female skull, male pelvis, female pelvis

The activity that we did with the students was called the “Skeleton in the Basement” activity. We modified this activity from the Smithsonian’s website. The students were given pictures of a skull and a pelvis and we asked to determine whether the skeleton was male or female. The students went through a checklist of features and decided whether each feature was male or female. The checklist is important because each skeleton can have both male and female features. What is important to consider is which features are more prevalent.

“These are the same bones, why do they look so different?” One of the students asked me this question before the class even started. They look different because they have different functions. All bones are different because of the life of the person to which they belonged. A person’s life is written in their bones, and this is what makes human osteology so interesting.

Week 8: Comparative Osteology

Physical anthropologists rely on osteology, or the scientific study of bones, to identify individual species, learn about the lives of an individual, or even to identify ancient illnesses (aka paleopathology). The skeletal features of bones reflect the life histories of individuals, and trained osteologists can use those features to identify the age, sex, diet, and, at times, even the cause of death of a particular specimen.

However, analyzing and comparing the bones from different species can also tell us about the evolutionary history of those species and the degree to which different species are related. For example, the overall form and organization of a dog’s skeletal features would be very similar to those of wolves, as those species are related. The same could be said for different species of fish, reptiles, turtles, etc.

In anthropology, osteologists often compare human skeletons with those of other primates so that we can learn about our ancient human past. In today’s activity, our TMSE students compared cranial features of human, chimpanzee, and coyote skulls, to learn about cranial capacity, dental formulas, diet, and the overall degree of similarity among species. For this activity, students were encouraged to think about the similarities and differences between each of the individual specimens. If they are similar, what makes them similar? If they are different, then how could we explain those differences in an evolutionary context?

To begin with, the students compared the skeletal characteristics of human, chimpanzee, and coyote skulls. Students were able to identify the human skull and distinguish it from the chimpanzee skull rather quickly, but additional analysis was needed to characterize precisely why the students thought they were so different.

skulls

The human chimpanzee skulls differed, for example, in the size of the teeth, the size of the cranium, and even the shape of the skull itself. Students also learned a new term, prognathism, to describe the degree to which the facial features extend out from the face. Chimpanzees are definitely more prognathic than humans, as are coyotes. However, the human and chimpanzee skulls were more similar to each other than they were to the coyote, which had a completely different structure.

 

In seeking a better way to describe the possible differences and similarities, we then analyzed two key features on each skull: teeth and cranial size.

To analyze the similarity in dentition, students were asked to come up with the dental formula for each specimen. A dental formula is essentially a count of the different types of teeth for a specimen, beginning with incisors (cutting teeth in the front of the mouth), canines (teeth for slashing), premolars (for stabilizing food and for grinding); and molars (grinders).

teeth

By counting the tooth types for the human, chimpanzee, and coyote skulls, our TMSE students figured out that humans and chimpanzees have the exact same dental formula! However, coyotes have a different formula.

Our students quickly ascertained that this similarity is likely due to the fact that humans and chimpanzees are related, both as primates and by our shared evolutionary past.

 

To continue to address some of these differences, we then compared the size of the cavity that houses the brain, also known as the cranial capacity.

cranial

By comparing across species, our students figured out that humans have the largest brain, followed by the chimpanzee, and then the coyote. After a lively discussion of the brain size of dolphins, humans, dinosaurs, and dogs, we reached the conclusion that our human brains are MASSIVE relative to our body size. Which, of course, means that we are intelligent creatures.

Our comparative analysis led us to hypothesize that the dental formula and cranial capacity may help determine whether a particular specimen is related to humans or not. To test out our theory, we then threw an unknown skull into the mix. After figuring out the dental formula, describing the tooth size, and looking at the cranial characteristics, our students concluded that the unknown skull was, in fact, related to humans because it shared a dental formula and had a cranial capacity that was in between that of the human and of the chimpanzees.

As it turns out, our students were absolutely correct! The unknown skull was Australopithecus afarensis, one of our evolutionary ancestors.

This activity ended up being a lot of fun, as everyone got a chance to handle castes of skulls and learn about how physical anthropologists may characterize skeletons. Moreover, by learning about basic skeletal features and interspecies variation, our students were able to conduct a comparative analysis of those features and to critically analyze the results based on that analysis.

All in all, a great day!

 

The lesson plan for this activity can be downloaded here.

Week 8 Skeletal Features