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paleoanthropology, genetics and evolution

Swartkrans

  • Mandibles of early Homo and robust australopithecines

    Mon, 2012-11-12 22:36 -- John Hawks
    Synopsis: 
    A lab showing the variation of mandibles in early members of our genus.

    For anthropologists, Africa was a point of exceptional diversity between 2 million and 1.5 million years ago. In both East and South Africa, the fossil record presents evidence of several different hominin species. Some fossils belong to our own genus, Homo, and others belong to robust australopithecines.

    These two forms seem like they should be easy to tell apart. Robust australopithecines had extraordinarily large mandibles compared to living humans. Consider:

    • The main part of the mandible, which holds the teeth, is called the mandibular corpus. In robust australopithecines, this is often extremely thick and tall, with a large distance from the inferior border of the mandible to the teeth.
    • The portion of the mandible that extends upward to articulate with the temporal bone is called the mandibular ramus -- with one on both left and right sides. The mandibular ramus of many robust australopithecines is exceedingly tall, reflecting the very vertically tall faces of these hominins.
    • Robust australopithecines have hugely expanded premolars and molars, and greatly reduced incisors and canines. Early Homo has overall larger teeth than in living humans, but the proportions between the molars, premolars, incisors and canines is very much like people today.

    However, despite these obvious differences, the mandibles of early Homo and robust australopithecines are not always so easy to tell apart. This station has several mandibles from robust australopithecines, mainly from Australopithecus robustus from Swartkrans and Kromdraai, South Africa. There are also several mandibles of Homo erectus here, and a handful of mandibles that are likely early Homo but not definitely H. erectus.

    Can you tell them apart? Try seriating these from most humanlike to most robust australpithecine-like. Is there a clear dividing line between the two, or are there questionable specimens?

    Study terms: 
    ramus
    corpus
    Australopithecus robustus
    Homo erectus
    Swartkrans
    Kromdraai
    Sangiran
    Tags: 
    mandible
    Anthropology 105
    laboratory
    anatomy
    Homo
    Homo erectus
    Australopithecus robustus
    Kromdraai
    Swartkrans
    Sangiran

  • 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

  • Meet Australopithecus robustus

    Thu, 2011-09-01 21:39 -- John Hawks
    Synopsis: 
    This lab station gives an opportunity to examine fossil casts of A. robustus in comparison to humans and apes.

    The region just north of Johannesburg, South Africa, is a formation of ancient limestone in which groundwater has formed numerous caves and sinkholes. Some of these caves are used by animals for cool shade, water, and minerals; some are used by leopards, or in ancient times, sabretooths. By accident and predation, the skeletons of animals fall or are dragged into these caves, including our relatives the hominins. After around 2 million years ago, the most common kind of hominin in these caves was a species we call Australopithecus robustus.

    The word "robust" refers to size and strength. A. robustus was not very large in body size, but it had exceptionally large molar and premolar teeth, and a very large and thick mandible, or jawbone. The main muscles of the jaw, the temporalis muscles, were so large that they ran up the complete height of the skull to meet at the midline. The high ridge of bone where these muscles attached to the top of the skull is called the sagittal crest.

    A. robustus is one of the best-represented species of early hominins. The first specimen to be found was TM 1517, a partial skeleton with cranial remains from Kromdraai, presently in the Cradle of Humankind World Heritage Site. The largest sample of A. robustus fossils come from Swartkrans, less than 3 km from Kromdraai. The iconic skull, SK 48, provides a good illustration of the anatomy of the cranium of A. robustus with its sagittal crest, large, thick cheekbones, and relatively large molar teeth.

    The most obvious features that A. robustus shares with living people are related to locomotion. Human bipedality, or upright walking, caused many changes to the skeleton. A simple comparison of the distal end of the femur, the end nearest the knee, is enough to tell that A. robustus was bipedal like humans. Quadrupedal animals, who go on all fours, very rarely support their weight on one leg and do not have to balance their centers of mass over a single point. Their legs are typically oriented straight from the hip joint to the ground. Humans, in contrast, have to support their weight on one leg every time they take a step. To accomplish this, their legs must angle from the hip joint under the body's center of mass. The human knee angles very obviously at the distal femur, so that when the condyles of the femur rest flat on the tibia (or a table), the shaft of the bone angles markedly from vertical.

    This angle is called the valgus angle, and is one of the easiest-to-see traces of bipedality in fossil hominins.

    Study questions: 
    1. Explore the fossil skulls of A. robustus in comparison to the human and ape skulls at this station.
    2. Which features are more humanlike?
    3. Which features are more like the ape skulls?
    4. What kinds of foods do you think A. robustus would have eaten?
    5. The femur provides key evidence of locomotion. Examine the valgus angle on the distal femur from Swartkrans. Is it more like a human or an ape femur?
    6. Looking at the femur of A. robustus from Swartkrans, how big do you think these creatures were?
    Study terms: 
    sagittal crest
    femur
    tibia
    valgus angle
    fossil
    species
    hominin
    cranium
    Australopithecus robustus
    Australopithecus
    Swartkrans
    Kromdraai
    Tags: 
    A. robustus
    South Africa
    explainer
    teaching
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