Question

Which characteristic is common to all the modern representatives of all major reptilian lineages (turtles, lepidosaurs, crocodilians, and birds)?

A) presence of four walking limbs
B) ectothermy
C) presence of teeth
D) presence of a notochord

Answer 1

All modern representatives of major reptilian lineages share the presence of a notochord during the embryonic stage, which is a characteristic of all chordates.

Step-by-step explanation:

The characteristic common to all the modern representatives of all major reptilian lineages, including turtles, lepidosaurs, crocodilians, and birds, is presence of a notochord. The notochord is a flexible rod-shaped body found in the embryonic stage of all chordates, which is replaced by the vertebral column in most adult forms. Although reptiles exhibit various forms of locomotion and limb structure, all share this early developmental feature. Birds, even though endothermic, also share this characteristic, as they are part of the clade that evolved from reptilian ancestors.

Answer 2

The characteristic common to all the modern representatives of all major reptilian lineages is B) ectothermy.

What is ectothermy?

Ectothermy, also known as cold-bloodedness, is the characteristic of being unable to regulate one's body temperature internally. This means that reptiles rely on external sources to maintain their internal body temperature. All modern representatives of all major reptilian lineages (turtles, lepidosaurs, crocodilians, and birds) are ectothermic.

While the other options are also characteristics of some reptiles, they are not common to all of them. For example, not all reptiles have four walking limbs (snakes and some lizards do not), not all reptiles have teeth (some lizards and turtles lack teeth), and not all reptiles have a notochord (birds have a vertebral column instead of a notochord).

Therefore, ectothermy is the only characteristic that is common to all modern representatives of all major reptilian lineages.