Chapter 17, Problem 23A

Summary Introduction

To evaluate:

Evidence that suggests the two given organisms are closely related.

Introduction:

Scientists believe that species sharing a common ancestor also share an evolutionary history. The evolutionary history of an organism is called its phylogeny. A system of classification that shows an evolutionary history of an organism is a phylogenetic classification and it reveals the evolutionary relationships of species.

Answer to Problem 23A

The two organisms shown in the figure are closely related as they share many morphological characters such as hollow bones, hip, leg, wrist, and shoulder structures. Some dinosaur fossils even showed feathers which is a character of birds.

Explanation of Solution

Characters are inherited features that vary among species. They can be morphological or biochemical. Based on shared characters, scientists construct patterns of descent or phylogenies. Shared morphological characters suggest that the species are closely related and evolved from common ancestor.

In the given figure an oviraptor and a sparrow are shown. Oviraptor is a dinosaur and sparrow is a bird. The two organisms share many common features. Some dinosaur fossils reveal that their bones had large hollow spaces just like the bones of birds. In this respect dinosaurs are more closely related to birds than reptiles like alligators and lizards which have more dense bones. alsotheropod dinosaurs have hip, leg, wrist, and shoulder structures that are more similar to birds than to reptiles. Recently some theropod fossils revealed that they had feathers too.

These evidences provided by morphological characters suggest modern birds are more closely related to dinosaurs.