Chapter 28.2, Problem 5MI

Summary Introduction

To define:

The term tetrapod.

Introduction:

Earliest tetrapods developed from flap finned fishes around 400 million years back in the Devonian Time. Tetrapods include all terrestrial vertebrates such as lions, hawks, turtles, and frogs. It also includes a number of animals which returned to life in the water such as sea lions, sea snakes, sea turtles, etc.

Explanation of Solution

An earliest tetrapod would have been animals similar to Acanthostega, with legs and lungs as well as gills, but still primarily aquatic and unsuited to life on land. Tetrapods evolved from a finned creature that lived in the water. Although this precursor was not like most of the fishes that are known today. Most creatures called fishes today are ray-finned fishes, the group closest to the root of this evogram. Ray-finned fishes include around 25,000 living species, undeniably more than the wide range of various vertebrates consolidated. They have blade rays — that is, an arrangement of frequently branching bony rays (called lepidotrichia) that exude from the base of the fin.