In this article we will discuss about the classification and nomenclature of animals.
Classification of Animals:
It is a matter of common observation that individuals related to one another tend to be similar and the degree of the similarity depends upon the degree of the kinship. Animals which are like enough to be included in the same species owe their likeness to descent from a common ancestor.
In classifying animals, zoologists are guided by two important principles:
(1) Animals, possessing similar structures and therefore descended from a common ancestor, are placed in the same natural group;
(2) Different groups of like animals agreeing with one another in some important feature and therefore related to one another, are included in a bigger group. In other words, classification is based on similarity of structure and descent from common ancestry.
Probably the first attempt to classify animals on a scientific principle was made by Aristotle (384—322 B.C.). He used structural similarity as the basis of classification-; but some of his-animal groups were artificial that is, the members of the group were not united IMF by a common ancestry.
Aristotle’s work was greatly perfected by Carolus Linnaeus (1707-1778). This Swedish biologist is referred to as the father of classification, because he devised the system that has been developed into the current Linnaean system of classification. In classifying animals into natural groups Linnaeus recognised certain grades or degrees of resemblance, which are spoken of as species, genera, families, orders, classes and phyla.
Species:
Each kind animal roughly corresponds to a species (plural, species). For example, man and dog each represents a species. A species may be defined as a group of individuals which resemble one another very closely and can mate with each other successfully for reproducing their own kind; interbreeding is seldom possible among animals belonging to different species.
Genus:
Two or more species agreeing in many important features are included in a genus (plural, genera). For example, the common Indian toad appears to be closely related to the American toad and the two species resemble one another; hence they are included in the same genus.
Higher Categories:
Genera having common characters constitute a family and likewise similar families are placed in an order, orders into a class, and classes into a phylum. The phylum (phylon=a race) is the largest subdivision of the animal kingdom.
There may be intermediate groupings in all these divisions, such as subphyla, super-classes, subclasses, suborders, etc. The terms family, older and class, are of course used in a special sense quite different from their ordinary meaning.
Phylogenetic Tree:
Relationship of the various animal groups may be represented by a branching tree-like diagram. Each leaf on the tree represents a species of animal. The fine shoot bearing the leaves constitutes a genus and the little twig that carries the shoots comprises a family. The small branch bearing the twigs represents an order and the big branch carrying the smaller ones is equivalent to a class.
The ten main branches of the phylogenetic tree bearing the larger branches compose the major divisions or phyla of the animal kingdom. The lowest and the most primitive group is placed near the bottom of the tree, whereas the highest group is placed near the bottom of the tree, whereas the highest group occupies the topmost position.
Nomenclature of Animals:
The common names of animals vary widely in different provinces of the same country and more than one common name is often applied to the same animal even in the same language. Linnaeus advocated the use of Latin for naming animals and thus prevented confusion.
The scientific name of an animal is composed of two Latin words; the first word stands for the genus and the second for the species. The system of using the generic and specific names is known as the binomial system of nomenclature.
The generic name is always written with a capital letter but the following specific name begins with a small letter. Moreover, scientific names must either be italicised or underlined. Thus the common Indian toad is Bufo melanostictus. Here the word Bufo represents the genus and the word melanostictus, the species.
The American toad is Bufo boreus; it belongs to the same genus Bufo, but is of a different species. The common Indian frog is known as Rana tigrina; it belongs to the genus Rana which is entirely different from the genus Bufo.
The European bull frog, Rana temporaria, is of the same genus as the Indian frog, but belongs to a different species. Similarly, the American bull frog is Rana catesbeiana and the leopard frog is Ranapipiens.
The toad family Bufonidae containing B. melanostictus, B. boreus, etc., and the frog family Ranidae containing R. tigrina, R. temporaria, etc., are included in the order Anura. The anura along with other orders form the class Amphibia of the phylum Chordata.