10
The Dinosaur Skeleton Objectives: 1. To learn the names of the bones of a vertebrate skeleton. 2. To be able to describe the differences between different dinosaur groups using skeletal terminology. 3. To be able to identify dinosaur bones as they are excavated. Procedures: Much of what we know about dinosaurs comes from the study of their bones. The similarity of the skeletons of various dinosaurs and humans is based on the common ancestry of all vertebrates (the subphylum of animals with an internal bony skeleton). We refer to the similarity in structures that is the result of evolutionary descent as a homology. Homologous structures need not have similar functions. For example, the wing of a bird and the arm of a human are homologous but do not have the same function. Structures with similar functions are called analogous structures. The Appendicular Skeleton (arms and legs) Examine the labeled skeleton of a human and the Camarasaurus. The dinosaur forelimb is essentially the same as our forelimb with one exception; we do not have a separate coracoid, a round bone between the scapula and humerus. The bones of the dinosaur hindlimb are comparable to the human leg. The primary difference between dinosaurs and humans is the ankle. Dinosaurs have two small bones the astralgalus and the calcaneum between the tibia and fibula and tarsal bones, whereas the humans do not have these bones. Don’t worry; we will not see these on the diagrams. The axial skeleton (skull, vertebra, ribs, and pelvis) The dinosaur skull is usually cited as evidence that dinosaurs are reptiles. Humans have a typical mammalian skull. The dinosaur skull is divided into several bones that are separate from each other while many of these bones in the human are fused. This is illustrated with the lower jaw or more correctly called the mandible. In humans, our jaw consists of one bone, while a dinosaur’s mandible is often divided into five bones. Another major difference is the hinge of a dinosaur jaw. Notice how the hinge of a dinosaur’s jaw is often at the back of the mandible and usually below the teeth. In humans, the mandible hinge is well above the teeth. We will complete a separate laboratory on the skull to see how this works. The dinosaur pelvis is an important structure that enables us to identify the two major groups of dinosaurs. The textbook, The Dinosaur Primer, shows the major bones of the pelvis. Lizard-hipped dinosaurs (saurischian dinosaurs) have a pelvis with a 90º or less angle between the pubis and ischium and the pubis has a large knob at the end. The bird- hipped dinosaurs (ornithschian dinosaurs) have a pubis without the knob and it pubis oriented backwards resulting in a long pubis with a forward prong and a backward prong. In humans the bones of the pelvis are fused, but the individual bones are still identifiable.
