Chapter 13

Fishes, Amphibians, and Reptiles

13.1 Lesson 13.1: Introduction to Vertebrates

Lesson Objectives

• Describe the general features of chordates.


• List the three groups of chordates with their characteristics.


• List the general features of vertebrates.


• Describe the classification of vertebrates.

Check Your Understanding

• What is the function of the notochord in lower vertebrates?


• What happens to the notochord in higher vertebrates?

Introduction

Itishardtobelievethatsomeoftheorganismsthatarechordatesarecloselyrelatedtousand
vertebrates like us - everything from fish to amphibians and reptiles, to birds and mammals.
Chordatesare a group of animals that includes the vertebrates, as well as several closely
related invertebrates. Some chordates, as we will soon see, appear to be nothing more than
animals resembling marine invertebrates, like the tunicates inFigure13.1. Chordates also
include the lancelets, which appear as mostly featureless and simplified swimming animals
(Figure13.2). What these all havein common, though, are certain characteristics appearing
either in the larval or adult forms, and which we will explore further in the first section.

Vertebrates all have backbones or spinal columns as well as some other defining character-