You excavate a fossil of a small reptile during a paleontology field trip. It has the following characteristics: skull with a pair of dorsal temporal openings and a pair of lateral temporal openings; bipedal with legs positioned directly under the pelvic girdle. Dating with radioisotopes shows that the specimen lived 100 million year ago (MYA). You conclude that the specimen belongs to which reptilian group (be specific as possible)?

Question

A.  anapsid
B.  synapsid
C.  diapsid
D.  archosaur
E.  dinosaur

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?

Gather Content
· What do you already know about reptile skulls and dinosaur adaptations?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

E.  dinosaur

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses reptile skulls and dinosaur adaptations.
· What type of thinking is required?
        o This question is asking you to analyze the information given, using logic, to dissect the problem and determine the answer.

Gather Content
· What do you already know about reptile skulls and dinosaur adaptations?
        o An important feature of reptile classification is the presence and number of openings behind the eyes. Reptiles’ jaw muscles were anchored to these holes, which allowed them to bite more powerfully. The first group to rise to dominance were the synapsids, whose skulls had one hole behind the openings for the eyes. (Anapsids had no openings – they are represented among extant reptiles only by the turtles.)
        o Diapsids have skulls with two pairs of holes on each side of the head, and like amphibians and early reptiles, they were ectotherms. A variety of different diapsids occurred in the Triassic period (213 to 248 mya), but one group, the archosaurs, were of particular evolutionary significance because they gave rise to crocodiles, pterosaurs, dinosaurs, and birds.
        o Among the early archosaurs were the largest animals the world had seen, up to that point, and the first land vertebrates to be bipedal—to stand and walk on two feet. By the end of the Triassic period, however, one archosaur group rose to prominence: the dinosaurs.
        o Dinosaurs evolved about 220 mya. Unlike previous bipedal diapsids, their legs were positioned directly underneath their bodies. This design placed the weight of the body directly over the legs, which allowed dinosaurs to run with great speed and agility. Subsequently, a number of types of dinosaur evolved to enormous size and reverted to a four-legged posture to support their massive weight.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Based on the two sets of holes in the skull, you can rule out the skeleton being an anapsid or synapsid. It must be a diapsid.
        o The bipedal stance with legs directly under the pelvis tells you that this diapsid was not only an archosaur – it was specifically a dinosaur.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o The question required you to analyze the information given, using logic, to dissect the problem and determine the answer.
        o Did you recognize that if there are two temporal openings on each side, it must be some kind of diapsid?
        o Did you recognize that the vertical placement of legs under the pelvis was a dinosaur adaptation?