GEOL 104 Dinosaurs: A Natural History

Fall Semester 2000
Comparative Anatomy II: The postcranium

The postcranium (everything posterior to the cranium), composed of:

(Incidentally, anatomical terms are for the most part based on Latin words. Bones or landmarks with Latin rather than English plurals are noted below)

Bones and Landmarks of the Axial Skeleton
Most of the axial skeleton is composed of the vertebral column, itself composed of individual vertebrae (singular, vertebra). Each vertebra contains the following sections:

  • Centrum (pl. centra): the large spool-shaped body
  • Neural arch: an arch of bone on dorsal surface of the centrum
  • Neural canal: the hole through which the spinal chord passes. (Popular conception to the contrary, the spinal cord does not pass through the centra
  • Transverse processes: bony extensions off the lateral sides of the neural arch, for attachment of muscles, tendons, ribs, etc.
  • Neural spine: bony extension off the dorsal surface of the neural arch
  • Various other prongs and crests off the neural arch and centrum, not dealt with in this class

    The vertebral column is divided into four sections in dinosaurs and their relatives:

    (Sometimes the sacral vertebrae are fused into a single unit, called a sacrum)

    Attached to the cervical and dorsal vertebrae are ribs (one on each side). Sacral ribs also exist, but are often fused to the pelvic girdle (see below). Instead of ribs, caudal vertebrae have chevrons, single bones which protect the nerves and blood vessels that run underneath the caudal centra.

    Ventral to the guts of dinosaurs and many other land vertebrates are gastralia (singular gastralium), or "belly ribs". In dinosaurs they are one or two pieces per side.

    Some dinosaurs have dermal ossifications or scutes: bones in the skin of the animal used for armor.

    Bones and Landmarks of the Appendicular Skeleton
    The appendicular skeleton is comprised of the limbs and their girdles (bones that attach the limbs to the axial skeleton.

    The Pectoral Girdle The forelimb is attached to the dorsal part of the axial skeleton by the pectoral girdle. The pectoral girdle is composed of the following bones:

  • Scapula (pl. scapulae): the shoulder blade
  • Coracoid: a bone on the ventral side of the shoulder blade. The shoulder joint of dinosaurs faces mostly posteriorly
  • Clavicle: collar bone. Paired and separate in most dinosaurs, but in meat-eating dinosaurs the clavicles are fused along the midline to form a single bone, the furcula (pl. furculae), or "wishbone".
  • Sternum (pl. sterna): the brestbone. In some dinosaurs it is composed of seperate sternal plates; in other it is fused. It is on the ventral surface of the chest

    The Forelimb

  • Humerus (pl. humeri: upper arm bone. Meets with the scapula & coracoid at the shoulder, and the radius and ulna at the elbow
  • Ulna (pl. ulnae): (generally) larger and more posterior of the forearm bones. The "funny bone" (techincally the olecranon process) is the backwards-pointing projection of the ulna.
  • Radius (pl. radii): smaller and more anterior of the forearm bones.
  • Manus (pl. manus): the hand. Composed of:

    The Pelvic Girdle The hindlimb is attached to the sacral part of the axial skeleton by the pelvic girdle (aka the pelvis (pl. pelves) or "hips"). The pelvic girdle is composed of three bones on each side:

  • Ilium (pl. ilia): the dorsalmost of the bones, which connects directly to the sacral vertebrae
  • Pubis (pl. pubes>: the lower pelvic bone that always attaches to the ilium anterior to the ischium (see below), although the shaft of the pubis in some dinosaurs points backwards
  • Ischium (pl. ischia): the lower pelvic bone that always attaches posterior to the pubis, and points posteriorly as well
  • Acetabulum (pl. acetabula): the hip socket, where the femur (see below) fits into the pelvis. In most vertebrates there is a sheet of solid bone formed by the pelvic bones on the medial surface of the acetabulum, but dinosaurs are specialized in having a perforate (opened) acetabulum (i.e., only a sheet of cartilage rather than bone on the medial surface).

    The Hindlimb Note that the structure of the hindlimb is very similar to that of the forelimb.

  • Femur (pl. femora: thigh bone. Fits into the acetabulum by the femoral head, and meets the tibia and fibula (below) at the knee. Often the single largest bone in the body (except for small running dinosaurs, in which the tibia is generally larger).
  • Tibia (pl. tibiae): the main shin bone. Generally thicker than, and medial to, the fibula
  • Fibula (pl. fibulae): smaller and lateral of the shin bones. Note that, popular misconception to the contrary, there is NO such bone as a "fibia"!
  • Pes (pl. pedes): the foot. Composed of:

    To Next Lecture.
    To Previous Lecture.
    To Syllabus.