Chapter 17, Problem 88TE

Scientists have found a number of fos-

sil turtles. One early fossil turtle did

not have a “shell” but did have wide,

expanded ribs along its back (“top”) side

and expanded belly coverings on the

belly (“bottom”) side. A second, more

recent turtle fossil had a full bottom shell.

Although this second fossil turtle did not have a full top

shell, it did have a partial shell extending from its backbone

as well as wide, expanded ribs. What do these two fossils tell

us about turtle evolution? Does it support the hypothesis

that turtles evolved in water rather than on land? ( Hint: If

the bottom shell evolved first, what kinds of predators did it

help defend turtles from?) Explain your answer.