Chapter 24, Problem 14A

Summary Introduction

Introduction:

The evolutionary tree is arranged like a family tree, and the branches reflect the phylogeny of species. The trunk shows the earliest animals and the branches reflect the evolution of the main phyla of animals from a common ancestor. The branching points on the evolutionary tree mark anatomical features in the animal's body plans.

Answer to Problem 14A

Correct answer :

The correct answer is option (D) Most animals have bilateral symmetry

Explanation of Solution

Explanation/justification for the correct answer :

Option (D) Most animals have bilateral symmetry. In the evolutionary tree, most of the animals are bilateral symmetry and these animals are flatworms, roundworms, rotiflers, mollusks, annelids, arthropods, echinoderms, and chordates. So, the correct answer is option (D).

Explanation for incorrect answer :

Option (A) True tissues evolved after bilateral symmetry. In the evolutionary tree, true tissues do not evolved after bilateral symmetry. It evolved before bilateral symmetry. So, this is an incorrect option.

Option (B) Segments evolved after bilateral symmetry. In the evolutionary tree, segments evolve only in chordates after formation of bilateral symmetry. So, this is an incorrect answer.

Option (C) The common animal ancestor was a sponge. Sponges are the only animals that do not have tissues. So, this is an incorrect answer.

Conclusion

Based on the evolutionary tree, most of the animals are bilateral symmetry. Hence, the correct answer is Option (D) Most animals have bilateral symmetry