Small Animal Care & Management - Fourth Edition - 3

Chapter 1

Introduction to Small Animal Care

a brieF hiStorY oF animaLS

w

hen and where on earth did life begin? Four theories are being
studied and debated by scientists around the world. These theories are that life began (1) in layers of rock; (2) in hot boiling water
around hydrothermal vents at the bottom of the oceans; (3) in slimy, porous
rock faces where the sea water laps against the shore; and (4) from comets,
meteorites, and asteroids
Paleontologists (those who deal with prehistoric life forms through the
study of fossils) have found fossils of microbes dating back at least 3.4 billion
years in rocks found in Australia and Southern Africa. Stromatolites
(layered structures created by the activity of primitive algae and bacteria)
have been found in these rocks. Other rocks of similar age found in
Australia contain sections known as cherts. These cherts show fossilized
remains of blue-green algae. Chemical analysis of even older rocks suggest
that photosynthetic organisms (organisms that convert light energy into
chemical energy) were present as early as 3.7 billion years ago. There are
rocks in Greenland dating back 3.85 billion years that contain a mix of
carbon isotopes, which would indicate life.
Researchers have discovered whole ecosystems (community of living
organisms and their environment interacting together to form a functional
unit) around hydrothermal vents on the ocean floor. These ecosystems
contain giant tube worms and blind shrimp. Sulfur-eating microorganisms
around the vents are, according to ribonucleic acid (RNA) analysis, the
closest living links to the first creatures on earth. RNA is an essential component of all cells.
Slimy, porous rocks where the sea laps against the land could have
provided the environment that helped organize organic molecules carried by the seawater into the building blocks of primitive life. Meteorites,
comets, and asteroids falling to earth may have carried amino acids
(compounds that contain both the amino (NH2) group and the carboxyl
(COOH) group; considered the building blocks of protein) and other
molecules necessary for life. High concentrations of amino acids have
been discovered inside meteorites found on earth and in gas clouds in
space. Some 2.2 billion years ago, free oxygen was present in the atmosphere. Living things used this reactive substance in the biochemical
functions of their cells. The free oxygen in the atmosphere also produced
a layer of ozone, which filters out the ultraviolet light from the sun that is
harmful to life. See Figure 1-1.
It is believed that the first land plants were established between 500 and
425 million years ago during the Ordovician period. This is also the period
of time when invertebrates (any animal without a backbone, or spinal column), such as arthropods and worms, appeared on land. These first terrestrial invertebrates fed on decaying plant material.
Vertebrate animals (animals having a backbone, or spinal column), in
the form of amphibians and reptiles, appeared during the Devonian period
between 405 and 345 million years ago. The bony fish appeared during the

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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
Small Animal Care & Management - Fourth Edition - vi
Small Animal Care & Management - Fourth Edition - vii
Small Animal Care & Management - Fourth Edition - viii
Small Animal Care & Management - Fourth Edition - ix
Small Animal Care & Management - Fourth Edition - x
Small Animal Care & Management - Fourth Edition - xi
Small Animal Care & Management - Fourth Edition - xii
Small Animal Care & Management - Fourth Edition - xiii
Small Animal Care & Management - Fourth Edition - xiv
Small Animal Care & Management - Fourth Edition - xv
Small Animal Care & Management - Fourth Edition - xvi
Small Animal Care & Management - Fourth Edition - xvii
Small Animal Care & Management - Fourth Edition - xviii
Small Animal Care & Management - Fourth Edition - xix
Small Animal Care & Management - Fourth Edition - xx
Small Animal Care & Management - Fourth Edition - xxi
Small Animal Care & Management - Fourth Edition - xxii
Small Animal Care & Management - Fourth Edition - 1
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Small Animal Care & Management - Fourth Edition - Cover4
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