Chapter 19, Problem 8STP

Summary Introduction

Introduction :

Ancestral characters and derived characters are used in cladistics to classify organisms according to the order in which they diverged from their common ancestors. An ancestral character is present in the common ancestors and within the entire line of descendants. Derived characters are not present in the ancestor but arose somewhere on the descended lineage.

Answer to Problem 8STP

Correct answer :

Option (D) wings used for flight.

Explanation of Solution

Explanation/justification for the correct answer :

Option (D) wings for flight. The subphylum Vertebrata is divided into Agnatha (the jawless vertebrates) and Gnathostomata (the jawed vertebrates). Gnathostomata is divided into two superclasses, Pisces and tetrapods. Tetrapods are divided into classes Amphibia, Reptilia, Aves, and Mammalia. The class Aves belongs to the members who can use wings for flight. This gain of feature is a derived trait and resulted in the branching event during evolution.

Explanation for incorrect answer :

Option (A) nervous system. The nervous system is an ancestral trait. It consists of the central nervous system, peripheral nervous system, and autonomic nervous system. Hence, it is an incorrect answer.

Option (B) organized system of tissues. It is also an ancestral trait as all the members of Vertebrata exhibit organ-system level of organization. Hence, it is an incorrect answer.

Option (C) role of ATP in mitochondria. It is also an ancestral feature and present in all the common ancestors used for energy generation. Hence, it is an incorrect answer.