Chapter 28, Problem 1STP

Summary Introduction

Introduction:

Amphibians include toads, frogs, salamanders, newts, and legless caecilians. Most amphibians are distinguished by moist skin without scales, four legs, exchange of gases through skin, a circulatory system with double loop, lungs, and aquatic larvae.

Answer to Problem 1STP

Correct answer:

The correct answer is option (B) rhipidstians.

Explanation of Solution

Explanation/justification for the correct answer:

Option (B) is rhipidstians. Many scientists agree that early tetrapods are most closely related to a group of now extinct lobe-finned fish named rhipidstians. The features that both early tetrapods and rhipidstians share include common bone structure in the skull and limbs, nostril-like openings in the tops of their mouths, and common tooth structure. So, the correct answer is option (B).

Explanation for incorrect answer:

Option (A) is ichthyostegans. Ichthyostegans have heavier leg bones, ankle and wrist joints, and stronger muscles. This group is also related to tetrapods but this is not the earliest relatives to amphibians. So, this is an incorrect option.

Option (C) is rays. Rays are cartilaginous fishes adapted to life on the bottom of the sea. In addition to their flattened bodies, their fins are enlarged and attached to their heads. They are not related to amphibians. So, this is an incorrect answer.

Option (D) is sharks. Sharks belong to the cartilaginous fishes. Most sharks have a streamlined shape with a pointed head and a tail that turns up the end. So, this is an incorrect answer.