The five-toed limb of stem reptiles became modified into a limb ____ in vertebrates that followed.
A) suitable for high-speed running
B) suitable for digging
C) suitable for swimming
D) with four fingers and an opposable thumb
E) with all of these

Question

Quizplus · Accepted Answer

The five-toed limb of stem reptiles evolved into different structures to adapt to different environments. In some vertebrates, it became modified for high-speed running (e.g. cheetah). In others, it became suitable for digging (e.g. moles). In aquatic vertebrates, it became modified for swimming (e.g. dolphins). And in primates including humans, it evolved into a limb with four fingers and an opposable thumb, which is suitable for a wide range of movements including grasping, manipulating objects, and tool use. Therefore, option E is the best choice as it includes all of these adaptations.

The Five-Toed Limb of Stem Reptiles Became Modified into a Limb