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 A105 Human Origins and Prehistory
A105 Spring 2002 Primate and Early Hominid Skull Activity

Station 1: Modern Primates
1. What three features separate the male gorilla skull from the female skull? What are these differences examples of?

  The male's skull is larger overall, has a sagittal crest, and has larger canines.  These are examples of sexual dimorphism.
 

2. Look at the lemur and rhesus macaque skulls.  What are their dental formulae?  Which one is the most derived?

    Lemur:  2.1.3.3 

    Rhesus macaque: 2.1.2.3 

 The rhesus macaque is more derived because it has lost a premolar; ancestral primates had additional premolars, as does the more primitive
lemur. 
 

3. Compare the rhesus macaque and squirrel monkey.  What are some general differences between these animals?  Don’t forget the teeth!

The squirrel monkey is smaller and has one more premolar; also, it is a New World monkey while the macaque is an Old World monkey.  

Station 2: Fossil Primates
4. Look at and briefly describe the Adapis cast.  Which of the modern primates does it most resemble?

Some things to note: postorbital bar but no postorbital closure (no bony orbit); long snout that is located between the eyes; eye sockets do not face
completely forward; overall size is small. The modern primate it most
resembles is the lemur. 

5. Compare and contrast the cast of Aegyptopithecus (brown cast) with the baboon.  How do the teeth differ from the squirrel monkey’s?

At first glance, Aegyptopithecus looks like a smaller version of the baboon
skull.  Its eyes face almost completely forward, and its canines are fairly large
compared to the rest of the teeth.  Of course, the baboon is much larger, and
its snout is completely beneath its eyes.  The most important difference
between the teeth of Aegyptopithecus and the squirrel monkey is that the
squirrel monkey has one more premolar, which indicates that Aegyptopithecus lived after the lineage leading to squirrel monkeys (and
indeed, all New World monkeys) had split from the Old World monkey/ape
line. 
 

6. Compare and contrast Proconsul and Aegyptopithecus.  What derived features are present in Proconsul?

Proconsul is larger than Aegyptopithecus, and has a larger brain.  Its canines
are slightly reduced compared to the rest of its teeth; this would be considered a derived feature.  Other derived features include the rounded
molar cusps, smaller snout, and larger size. 

Station 3: Australopithecines.
1. How does Australopithecus africanus differ from the robust australopithecines?

A. africanus has a slightly smaller brain than robust australopithecines.  The biggest difference has to do with the teeth.  Robust australopithecine molars are larger than africanus molars, and their incisors are smaller, both in overall size and in relation to the molars.  A. africanus also has a more lightly built face, while robust australopithecines have heavy zygomatics and dished faces.
 

2. Compare Australopithecus boisei to the chimpanzee.  What differences do you notice, especially in their teeth?  Why do you think we observe these differences?

A. boisei has a larger brain and more massive mandible.  Its dental proportions are also very different, with small incisors and huge molars.  This indicates a difference in diet; chimpanzees rely more on slicing and stripping with their incisors than A. boisei seems to have, and A. boisei relied more on foods that required more grinding with molars.
 

3. Look at Australopithecus aethiopicus.  What similarity do you notice with the gorilla?  What might cause this?

A. aethiopicus, like the gorilla, has a sagittal crest.  This might indicate a dietary similarity -- or at least, the development of very strong chewing muscles, which attach to the sagittal crest.

4. Are the dental features of the robust australopithecines primitive or derived traits?  You may use the chimpanzee skulls for comparison, but remember that these traits are truly being compared to the common ancestor of hominids and chimpanzees.

The robust australopithecine dental features are derived traits; they are not seen in chimpanzees and are more extreme than seen in earlier hominids.  They are an adaptation to a diet high in foods requiring grinding, such as nuts and seeds.

5. What trends do you see in the morphology of australopithecines through time?

Brain size increases in the australopithecine lineage in general; molar size increases, faces become more robust, and the nuchal area on the occipital becomes smaller.  Robust australopithecine molars show this trend more than graciles'; robust australopithecines also have very reduced incisors, and their faces become even more massive than the graciles', along with their mandibles.