Chapter 28.2, Problem 3MI

Summary Introduction

To define:

The given term “adaptive radiation” using a book or a dictionary.

Introduction: Fishes are vertebrates that have characteristics allowing them to live in water. There are three classes of fishes based on their body structure- jawless fish, cartilagenous fish and bony fish. Ancient extinct fishes had features that enabled them to evolve into modern fishes.

Answer to Problem 3MI

The process of evolution that produces many species from an ancestral species is called adaptive radiation.

Explanation of Solution

According to the phylogeny of fishes, the first fish were jawless and toothless but had gills, heads and tails. Ostracoderms were the next group of fishes to appear in fossil record. These fishes had bony head shields, a bony outer covering and paired fins. They were jawless filter feeders. Scientists believe that modern fish share an ancestry with ostracoderms.

During Devonian period, modern fishes had their beginnings. Some fishes were jawless while some such as placoderms had jaws, a covering of bony plates, paired fins, and an internal skeleton. Three of these features are characteristics of the fishes that replaced placoderms as they became extinct. The Devonian period is often referred to as the Age of Fishes because of the adaptive radiation of fishes that occurred at that time. Adaptive radiation or divergent evolution occurs in a very short span of time when one species gives rise to many species in response to the creation of new habitat.