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paleoanthropology, genetics and evolution

thoracic

  • Laboratory inquiry 1: Outgroup

    Mon, 2013-02-04 00:10 -- John Hawks
    Synopsis: 
    A laboratory station giving information about the skeleton of the mongoose lemur

    Your task in the first laboratory inquiry assignment is to develop a hypothesis about the anatomy of the common ancestor of two species of anthropoid primates. To accomplish this, you will need to consider the anatomy of an outgroup, in this case a species outside the anthropoids.

    In the previous laboratory, you were able to examine a skull of a prosimian primate as an outgroup. That can work very well as a way to compare the anatomy and number of teeth and other features of the cranium. But to compare postcranial anatomy you will need to have a complete skeleton of a prosimian primate.

    Unfortunately, we don't have one in the laboratory. Instead, we'll consider some features of the skeleton of the mongoose lemur here:

    Lemur skeleton illustration

    The mongoose lemur has a body between 30 and 45 centimeters long, with a long tail. Its natural habitat is in northern Madagascar, and it also can be found today in the Comoros Islands.

    As you can see from the picture, the mongoose lemur's skeleton has arms and legs nearly the same length, with its legs just a bit longer than the arms.

    The skeleton has 12 thoracic vertebrae and 7 lumbar vertebrae. It also has a long tail.

    The mongoose lemur's scapula is relatively long and narrow. This is contrast to a human scapula, which is triangular in shape with a very broad superior border.

    As you formulate a hypothesis about the anatomy of the common ancestor of your anthropoid species, this information will assist you.

    Study terms: 
    lumbar
    thoracic
    Tags: 
    laboratory
    Anthropology 105
    lemurs
    anatomy

  • Primate vertebral numbers

    Sun, 2011-09-18 20:36 -- John Hawks
    Synopsis: 
    A laboratory exercise to explore the numbers of vertebrae in different primates.

    Between the skull and the sacrum, humans have 24 vertebrae. Well, most humans, anyway. Sometimes humans have a few more or less.

    Humans vary in the length of the lumbar region, the number of vertebrae between the lowest ribs and the pelvis. The typical number is five, but some people have only four. Rarely, people have six lumbar vertebrae.

    Non-human primates also vary in the number of lumbar vertebrae. This variation is connected to locomotion. Species with vertical, suspensory postures have relatively short lumbar columns. Chimpanzees, gorillas and orangutans have fewer lumbar vertebrae than humans. Quadrupedal primates, including most monkeys and prosimians, have longer lumbar columns than humans.

    What to do: This station has several skeletons of different kinds of primates — both New World and Old World monkeys and apes. Determine the number of lumbar vertebrae in each of these primates. Do these primates vary in the other segments? Do they ,for instance, have the same number of ribs?

    Anatomy of the vertebral column
    Study questions: 
    1. Consider the number of lumbar vertebrae in gorillas and orangutans. Explain how these apes each have relatively few lumbar vertebrae and humans have more than either. What do you suppose was the number of vertebrae in the common ancestors of these apes and humans?
    2. Why do quadrupeds have a longer lumber spine?
    3. Why do you think there is very little variation in the cervical spine?
    Study terms: 
    lumbar
    cervical
    thoracic
    posture
    locomotion
    New World monkeys
    Old World monkeys
    apes
    hominoids
    Tags: 
    Anthropology 105
    explainer
    laboratory
    anatomy
    primates
    vertebrae

  • The anatomy of a vertebra

    Sun, 2011-09-18 20:23 -- John Hawks
    Synopsis: 
    A laboratory exercise to introduce the anatomical features of vertebrae.

    Each vertebra has several parts. The most important are:

    Body
    The largest part of the vertebra, this is a cylindrical column of spongy bone, padded by cartilaginous discs above and below.
    Vertebral foramen
    The hole in the center of the vertebra, through which passes the spinal cord.
    Spinous process
    A projection on the posterior aspect of the bone, together these form the ``spine'' that can be felt from outside the skin.
    Transverse processes
    Left and right, these project from the vertebra allowing muscular and ligamentous attachments.

    Additionally, the first two vertebrae below the head are special in their anatomy. The first, called the atlas, holds up the head and lacks any vertebral body. Its anatomy is like a simple ring of bone. The second, the axis has a large projection from its superior surface, called the dens, or odontoid process, which stabilizes rotation of the neck.

    The rest of the vertebrae are slightly different from each other, depending on the part of the spine. The transverse processes of the cervical vertebrae tend to be split, or bifid, as are the spinous processes of C3-C6. The thoracic vertebrae have articular surfaces for the ribs, called rib facets, and their spinous processes are long and directed downward (caudally). The lumbar vertebrae have very large and thick vertebral bodies and stout spinous processes.

    Anatomy of the vertebral column
    Study terms: 
    spinous process
    transverse process
    cervical
    thoracic
    lumbar
    sacrum
    vertebral foramen
    vertebral body
    Tags: 
    Anthropology 105
    laboratory
    explainer
    vertebrae
    anatomy

  • The different types of vertebrae

    Sun, 2011-09-18 20:17 -- John Hawks
    Synopsis: 
    A laboratory exercise to introduce the different segments of the vertebral column

    The spine extends from the head to the sacrum, and in most people consists of 24 vertebrae. The vertebral column can be divided into three segments:

    Cervical
    The first seven vertebrae, all in the neck. These are smaller and lightly built.
    Thoracic
    Twelve vertebrae, each articulating with the twelve pairs of ribs.
    Lumbar
    The lower five vertebrae, between the ribs and the sacrum. These have the largest vertebral bodies.
    Anatomy of the vertebral column

    Each of the three segments of the spine has a curve. The cervical spine and the lumbar curve both are convex anteriorly, while the thoracic spine curves the opposite way, convex posteriorly. Each vertebra is shaped a bit like a wedge to support these curves, especially noticeable with the five lumbar vertebrae. The lumbar curve is unique to humans, allowing us to maintain a vertical posture above our pelvis.

    Study terms: 
    vertebra
    lumbar
    thoracic
    cervical. sacrum
    ribs
    Tags: 
    Anthropology 105
    explainer
    laboratory
    vertebrae
    anatomy
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