john hawks weblog

paleoanthropology, genetics and evolution

eruption

  • Aging juvenile fossil hominins

    Tue, 2011-10-25 00:27 -- John Hawks
    Synopsis: 
    Laboratory exercise giving the opportunity to examine the development of juvenile hominin jaws.

    The fossil record is not made up only of adults. We have abundant skeletal evidence from juvenile individuals of a broad range of ages. At this station you will find model mandibles and maxillae from human children of a range of ages. These provide a comparison for the casts at the station, each of which represents a fossil hominin specimen from Africa, between 3.6 million and 1.5 million years ago.

    The mandibles represent several different species. They include:

    1. OH 7, from Olduvai Gorge, Tanzania. This is the type specimen of Homo habilis, around 1.75 million years old.
    2. MLD 2, from Makapansgat, South Africa. This is an early specimen of Australopithecus africanus, around 2.7 million years old.
    3. LH 2, from Laetoli, Tanzania. An early specimen of Australopithecus afarensis, it is around 3.6 million years old.
    4. SK 47, from Swartkrans, South Africa. This is a juvenile specimen of Australopithecus robustus, around 1.5 million years old.

      5. A selection of other mandibles, including some adult mandibles of the same species, is also available. Examine these in comparison with the modern dental models. Which teeth are present in the fossil specimens? What teeth are in the process of eruption? What do they tell you about the ages of the individuals?

    Study terms: 
    eruption
    occlusion
    Laetoli
    Koobi Fora
    Swartkrans
    Homo habilis
    Australopithecus afarensis
    Australopithecus africanus
    Makapansgat
    Tags: 
    A. afarensis
    A. africanus
    Australopithecus
    Homo
    development

  • Deciduous teeth

    Mon, 2011-10-17 23:59 -- John Hawks
    Synopsis: 
    Laboratory exercise introducing eruption of deciduous dentition in humans and primates.

    Like most mammals, humans have two sets of teeth. The first set is called the deciduous dentition, but you probably know these as "baby teeth."

    The human deciduous dentition includes two incisors, one canine, and two molars in each quadrant. When people lose their deciduous molars, these are replaced by permanent premolars. The permanent molars do not have deciduous teeth in their places before them.

    Deciduous teeth are abbreviated with a "d" and the tooth type and number in lowercase. For example, the deciduous lower first molar is a dm1; the upper left deciduous canine is luc.

    What to do: Consider the series of models at this station. They represent the mandibular dentitions of children at different ages during their development. Can you determine the order that the permanent teeth erupt and replace the deciduous teeth? For example, are the permanent incisors the first to erupt? The permanent molars?

    Part 2

    There are several kinds of primate represented at this station. These primates have different adult body sizes, and grow at very different rates. Nevertheless, their teeth erupt in sequences that are very much like the human dental eruption sequence.

    Yet, there are exceptions. Many primates erupt their canine teeth relatively late in their eruption sequence. In humans, the upper canine typically erupts before the second molars. In many primates, the canine is delayed in development compared to the second molars.

    What to do: Examine the primate dentitions at this station. Identify the deciduous and permanent teeth that you see in each. Try to think about what age a human would likely be, with the same teeth present. Can you find aspects of tooth eruption that differ between humans and these primates?

    Study terms: 
    eruption
    deciduous
    Tags: 
    Anthropology 105
    explainer
    laboratory
    teeth
    development

  • Wisdom teeth

    Tue, 2011-10-11 08:12 -- John Hawks
    Synopsis: 
    Laboratory exercise to introduce third molar variation.

    Most humans have three molars, but many — especially in America — have their third molars (called wisdom teeth) extracted. Some people do not develop third molars at all, or they never erupt into occlusion.

    Humans are not alone. Some other kinds of primates have entirely lost their third molars and normally erupt only two in each quadrant. The South American monkeys called callitrichids (marmosets and tamarins) are small-bodied monkeys who normally have only two molars in each quadrant of the jaw.

    Many people begin to develop third molars within their jaws, but the teeth never erupt. Others don't have any development of the third molars at all. We may not know about this unless we learn it from X-ray images. Sometimes teeth are extracted before they emerge from the jaw, or erupt, but typically any problems become apparent at or after eruption.

    We are interested in showing whether third molar eruption or extraction can be correlated with any of the measurements you took earlier in the semester. In the spreadsheet, for each of your third molars, indicate whether you have it in the tooth row now, whether it has been extracted, or whether it never erupted at all.

    The two incisors, one canine, two premolars and three molars on both top and bottom are called the human dental formula. We write a dental formula as follows:

    2 1 2 3
    ___________
    2 1 2 3

    What is the dental formula of a human who has never erupted her upper wisdom teeth, but who has the lower ones?

    Study terms: 
    wisdom teeth
    molar
    eruption
    callitrichid
    Tags: 
    Anthropology 105
    explainer
    laboratory
    teeth
Subscribe to eruption

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