article : Understanding and Content the Study of Animals

An Introduction to Zoology

By Laura Klappenbach, About.com

Zoology is the study of animals (Gr. zoon, animal + logos, to study). This sounds like a simple definition, but upon further clarification, the "study of animals" turns out to be a broad and complex subject matter. The "study of animals" calls upon many other scientific disciplines including:

• biology
• chemistry, biochemistry, and molecular biology
• genetics
• population biology
• evolution and paleontology
• comparative anatomy
• ethology
• ecology, biogeography, and conservation biology

Like all forms of life on our planet, animals have changed over the course of millions of years. To help in the understanding of our planet's history, time is broken down into the following units (in order of descending duration):

• Eon
• Era
• Period
• Epoch

The three eons of Earth's history include the Archean Eon (4600 - 2500 Ma YBP*), the Proterozoic Eon (2500-590 Ma YBP), and the Phanerozoic Eon (590-0 Ma YBP). The Phanerozoic Eon differs from the preceeding Archean and Proterozoic Eons by a sharp increase in the diversity of multicellular lifeforms. During Phanerozoic Eon, notable events in animal evolution include:

• First vertebrates appeared (Paleozoic Era, Cambrian Period)
• Fishes and invertebrates diversified (Paleozoic Era, Ordovician Period)
• First terrestrial plants and animals (Paleozoic Era, Silurian Period)
• First amphibians (Paleozoic Era, Devonian Period)
• First reptiles (Paleozoic Era, Carboniferous Period)
• Insects and reptiles diversify (Paleozoic Era, Permian Period)
• Reptiles diversify, first dinosaurs (Mesozoic Era, Triassic Period)
• First mammals, first birds, dinosaurs dominate then mass extinction event (Mesozoic Era, Jurassic Period)
• Origin of human family (Cenozoic Era, Tertiary Period, Pliocene Epoch)

* Please note: The notation 'Ma YBP' indicates "million years before present".

A fundamental requirement for the study of animals, is a classification system; a way of assigning names and illustrating relatedness between animals. This naming system, called bionomial nomenclature assigns a two-part name to each organism (this naming convention is applied to all lifeforms, not just animals). The two-part name is based on the organism's genus and species (the two most granular levels of classification). The full classification of an organism includes its placement into the following heirarchy (groups listed below in order of ascending specificity):

• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

The body of scientific fact and theory that comprises zoology, like all other sciences, has been acquired (and continues to expand) by the application of the scientific method. The scientific method is an approach to gathering, interpretting, and applying facts and observations to expand our knowledge of the world around us. The scientific method is a process consisting of the following basic steps:

1. Make observations
2. Formulate hypothesis (or question)
3. Design an experiment (that will answer the question)
4. Perform experiment and collect data
5. Interpret data
6. Form conclusions