Small Animal Care & Management - Fourth Edition - 7

Chapter 1

Introduction to Small Animal Care

With the extinction of the dinosaurs, an opportunity arose for smaller
creatures to evolve and become abundant. During the Paleocene and Eocene
epochs 70 to 40 million years ago, placental mammals evolved, dispersed,
and adapted to new environments. Placental mammals have a placenta
through which the embryo and fetus are nourished while in the uterus.
Many of the small animals discussed in this book are placental mammals
and evolved during this period.

cLaSSiFication oF orGaniSmS
Taxonomy is the science concerned with the naming and classification
of organisms. The Greek philosopher and biologist Aristotle is credited
with the first attempts at classifying organisms based on their structural
similarities. An English naturalist, John Ray (1627-1705), developed a
more comprehensive system of classification, but Carolus (Carl) Linnaeus
(1707-1778), a Swedish botanist, is credited with developing our modern
method of classification.

Linnaeus's System of classification
Linnaeus's system has been expanded since then and today is made up of
seven categories, or taxa. These categories are kingdom, phylum, class, order,
family, genus, and species. These categories can be subdivided into finer
categories, such as subphylum or subclass. Today, about 30 different taxa are
recognized.
In Linnaeus's system, all organisms are divided into one of five
kingdoms:
1. Monera are the bacterial organisms that lack a true nucleus in the cell,
and reproduce by fission.
2. Protista are typically single-celled, microscopic organisms that contain
a nucleus. They include the algae and protozoa. Algae contain chlorophyll, but lack stems, roots, and leaves. Protozoa are animal-like, usually
live in water, and are important because many are disease-causing
organisms.
3. Plantae include all land plants. They are multicellular photosynthesizing organisms.
4. Fungi are molds, yeasts, and fungi.
5. Animalia is composed of the invertebrates and vertebrates.
All animals discussed in this book belong to the phylum Chordata in
the kingdom Animalia. All members of this phylum have the following four
distinctive characteristics:
1. an embryonic notochord, which is usually replaced by the spinal cord;
2. a dorsal tubular nerve cord running down the back side;
3. pharyngeal or throat area gill slits; and
4. a rear-area tail.

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Table of Contents for the Digital Edition of Small Animal Care & Management - Fourth Edition

Contents
Small Animal Care & Management - Fourth Edition - Cover1
Small Animal Care & Management - Fourth Edition - Cover2
Small Animal Care & Management - Fourth Edition - iii
Small Animal Care & Management - Fourth Edition - iv
Small Animal Care & Management - Fourth Edition - Contents
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