Manta rays, sting rays, and eagle rays are similar to lampreys in that they have cartilaginous skeletons. How are they different from lampreys?

Question

A.  They have closed circulatory systems.
B.  They have gills.
C.  They have jaws.
D.  They have bony fin lobes.

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 the evolution of the jaw?

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

C.  They have jaws.

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses the evolution of the jaw.
· What type of thinking is required?
        o This question is asking you to take what you already know and apply it to this unfamiliar situation.

Gather Content
· What do you already know about the evolution of the jaw?
        o An important evolutionary advance in the late Silurian was the development of jaws. Jaws evolved from gill arches, which in jawless fish were cartilaginous struts used to reinforce the tissue between gill slits to hold the slits open.
        o Each gill arch was formed by a series of several cartilages (which later evolved to become bones) arranged somewhat in the shape of a V turned on its side, with the point directed outward. Imagine the fusion of the front pair of arches at top and bottom, with hinges at the points, and you have the primitive vertebrate jaw.
        o Armored fishes called placoderms and spiny fishes called acanthodians both had jaws. Spiny fishes and ostracoderms had internal skeletons made of cartilage, but their scales contained small plates of bone. Spiny fishes were jawed predators and far better swimmers than ostracoderms, with many fins reinforced with strong spines.
        o The diverse and successful placoderms dominated the seas of the late Devonian. The placoderm jaw was much improved over the primitive jaw of spiny fishes, with the upper jaw fused to the skull and the skull hinged on the shoulder.
        o At the end of the Devonian period, these pioneer vertebrates were replaced by sharks and bony fishes.
        o In these fishes, the jaw was improved even further, with the upper part of the first gill arch behind the jaws being transformed into a supporting strut or prop, joining the rear of the lower jaw to the back of the skull. This allowed the mouth to open much wider than was previously possible. Soon, sharks became the dominant predators in the sea.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Like their relatives the sharks, rays have jaws. Lampreys do not.

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 take what you already know and apply it to this unfamiliar situation.
        o Did you recognize that a major innovation of the cartilaginous fish was the refinement of the jaw?