Chapter 28, Problem 12STP

Summary Introduction

To explain:

The reason that the notochord is considered an evolutionary advancement.

Introduction:

The chordate animals have four distinctive features: a dorsal tubular nerve line, a notochord, a pharyngeal pouch, and a postanal tail. All chordates also might have some form of a thyroid gland. Most of the chordates are vertebrates.

Explanation of Solution

Notochord is a flexible, rod-like structure that stretches the body length. It is situated just below the spinal cord of the tubular nerve. In most vertebrates, the notochord is gradually replaced by bone or cartilage. The notochord persists in invertebrate chords. The versatility of the notochord makes it possible for the body to stretch rather than shorten during contractions of the muscle segments. An animal with a notochord will allow side-to - side motions of the body and tail, the first time that fish-like swimming is made possible in the history of evolution.

Conclusion

Thus, notochord is considered an evolutionary advancement as it develops into the vertebral column in vertebrates.