Dinosaur skull lab Objectives A dinosaur skull is an example of evolutionary engineering. Some dinosaurs, such as Tyrannosaurus, have the problem of possessing large heads; however, evolution has selected for adaptations to help strengthen the skull without adding more weight. In this laboratory you will study dinosaur skulls to help understand the special skull adaptations of these animals. Skull features Dinosaur skulls have two pairs of openings, called lateral fenestra, behind the orbits (the opening for the eye) on each side of the skull, and two supratemporal fenestra near the top of the skull above the lateral fenestra. This type of skull is referred to as a diapsid skull. A second feature of dinosaur skulls is the location of the mandible hinge on the skull. Note that the mandible articulates with the cranium on a line at or below the teeth. Our mandible has a hinge that articulates well above the teeth. Dinosaur skulls also came in parts, whereas mammal skulls like ours are fused into one large bony structure. Look at the mandible of Camarasaurus. Note how it is in sections. You may see the sutures (lines in the bones) that formed the various bones of the skull. The teeth are part of the dentary section. The part of the skull that articulates with the cranium is called the articular.

Major landmarks of the Camarasaurus skull. L is the lacrimal bone, J is the jugal bone, and sf is the supratemporal fenestra. The arrow shows where the muscles, which when contracted opened the mouth, were attached.

The cranium is also divided into parts. These are also easily seen in Camarasaurus (look for what appears to be cracks or lines in the skull). The premaxilla is the most anterior or forward part of the skull. It includes the front of the nares (nostrils) and the front teeth. The side of the cranium with the back teeth is the maxilla. It connects to the premaxilla, which has the front

teeth, and it extends to the preorbital fenestra. The fenestra are openings in the skull, which help lessen the weight of the skull, but like struts they help to reinforce it. Below the orbit is the jugal bone (J). The lateral fenestra is just behind and below the orbit. The bone directly in front of the orbit is the lacrimal bone, which sometimes produces a knobby horn in front of the eyes in carnivorous dinosaurs. At the back behind and above the orbit is the supraorbital fenestra. Muscle attachments. All muscle activity involves antagonistic muscles. That means there are muscles that act opposite to each other. No movement of any part of our body or a dinosaur body acts without muscle contraction. For example, muscles on the inside of the jaw connect with the skull, and their contraction causes the jaws to close. Muscles on the articular that connect the back of the jaw to the back of the skull contract to open the jaw (the connection point is shown by the arrows on the Camarasaurus skull).

The dinosaur Diplodocus, a relative of the Camarasaurus, is an interesting case study of skull modifications. Examine the illustration below. The landmarks are as follows n- nares, o – orbit or eye socket, m- maxillary, p – premaxillary, d – dentary, af- preorbital fenestra, lf- lateral fenestra, and sf- supratemporal fenestra. Also you can clearly see how the muscles from the mandible (lower jaw) to the skull, when contracted would open the mouth, aided by the pivot point, which is anterior the muscle attachment.

Finally, note that the nares is on top of the head. In mammals, such as the elephant, their nares also opens up on the top of the head and some paleontologists have suggested that Diplodocus might also have had a trunk, but others think that the skin covered most of the nares and the nostrils, the actual openings, were in fact farther down on the skull.

Using the labeled skulls of Diplodocus and Camarasaurus as a guide, identify the various bones in the skull of an Allosaurus 1. Bone 2 is the

a. dentary b. maxilla c. premaxilla d. articular e. jugal 2. Bone 1 is the a. dentary b. maxilla c. premaxilla d. articular e. jugal 3. Bone 3 is thea. dentary b. maxilla c. premaxilla d. nares e. fenestra 4. The space marked as 8 is the a. lateral fenestra b. nares c. orbit d. preorbital fenestra 5. The space marked as 9 is the a. lateral fenestra b. nares c. orbit d. preorbital fenestra

6. The space marked as 6 is the a. lateral fenestra b. nares c. orbit d. preorbital fenestra 7. The space marked 7 is the a. lateral fenestra b. nares c. orbit d. preorbital fenestra

8. The nares is the a. eye opening b. nasal opening c. connection to the spine 9. The orbit is the a. eye opening b. nasal opening c. connection to the spine 10. The bone forming the horny knob on the Allosaurus is the a. jugal b. lacrimal c. quadratojugal d. dentary e. maxilla