Taxonomic Classification
and
Nomenclature

 

 by

 Tim Keynes

Have you ever wondered what that long, hard to spell and impossible to pronounce name you have to write in your permit books is all about?

Well, it is the scientific name given to a particular species of animal that separates it from all others.    It can tell you how one particular species of animal is related to other species of animals, and since Latin or latinised derivatives are used; it usually tells you something about the animal itself.

Anyway, I have decided to attempt to explain the general principles that lie behind these names in the following pages.    If you don’t get past the first few paragraphs I wouldn’t blame you, but if you read on you may find the process more interesting than you first thought.

TAXONOMY

Taxonomy is the science which attempts to provide a logical system of classification and nomenclature for the diverse organisms which have inhabited the earth since life began more than 1,000 million years ago.    These organisms are collectively known as the earth’s biota, while all living organisms comprise the earth’s biosphere

Despite the increasing number of extinctions resulting from human activity, the biosphere is tremendously diverse.    About two million types of living organisms have been classified and named by taxonomists, while it is probable that there are many more types which have yet to be brought to their attention.   In addition, the fossil record has revealed the existence of numerous types of organisms which are now extinct.    Thus, the total number of types of organisms comprising the earth’s biota could be several hundred million.   Without taxonomic classification and nomenclature it would be impossible for the biological sciences to deal with this diversity of organisms. 

Taxonomic classification involves the grouping of organisms into taxa (plural).   A taxon, (singular) is a class into which a group of organisms is placed because all members of the group possess some common characteristics.    In modern phylogenetic (phylogeny = evolutionary history) systems of taxonomic classification the characteristics chosen as criteria for grouping organisms into taxa are those which reflect the evolutionary relationships of the organisms and thus their genetic similarities and differences. 

Taxonomic nomenclature involves the naming of taxa.    The function of the names given to taxa is classification.    Throughout history, as people have needed to communicate about specific organisms, they have given them common names.    These common names usually have only local significance, since the same type of organism may be given different common names in different localities.    Also, the same common name is often given to several different types of organism.    Because of the inconsistency of common names, they tend to hinder rather than help communication in the biological sciences.    For this reason, a standard procedure for naming taxa has been devised using Latin or latinised words. 

CLASSIFICATION 

Various phylogenetic systems of taxonomic classification have been proposed, however all of the modern systems use the same hierarchy of categories in the classification of organisms.

The main categories are:-

species
genus
family
order
class
phylum
kingdom 

Intermediate categories (subfamily, superclass, subphylum, etc.) are often used to indicate secondary phylogenetic relationships within or between taxa in the major categories.    Also, all of the modern systems use the same basic unit of classification.    This is not the individual organism, but the gene pool (or Mendelian population) of organisms.

A species is comprised of all populations which are capable of interbreeding to produce fertile progeny.    These populations may not, in fact, interbreed because they are reproductively isolated by habitat discontinuities and/or time-distance barriers.    Reproductive isolation often leads to divergence in morphology and/or behaviour among the populations comprising a species so that it is necessary to recognise subspecies and varieties.

Two or more species which are closely related (in terms of phylogeny) may be grouped into a single genus.    In turn, two or more closely related genera may be grouped into a single family and so on through the order, class, phylum and kingdom categories.    All of the kingdoms together comprise the earth’s biota.

The highest category of all classification systems contains a single taxon, the earth’s biota (all species populations both extinct and living).    In the kingdom category, four taxa are recognised:- 

MONERA   (simple unicellular organisms)
PROTISTA (complex unicellular organisms)
METAPHYTA (multicellular plants)
METAZOA  (multicellular animals)

                              

In this article we will only be concerned with getting to marsupials, therefore only the METAZOA kingdom, which contains 26 living phyla, is of interest:-

 

PORIFERA (sponges)
CNIDARIA (sea anemones, jellyfish)
CTENOPHORA (comb jellies)
PLATYHELMINTHES (flatworms)
NEMERTINA (ribbon worms)
ACANTHOCEPHALA (spiny-headed worms)
ROTIFERA (wheel animals)
GASTROTRICHA  (scaled worms)
KINORHYNCHA  (spiny-skinned worms)
NEMATODA (roundworms)
PRIAPULIDA (priapus worms)
ENTOPROCTA (tentacled, stalked animals)
ANNELIDA (earthworms, fan worms)
ARTHROPODA (insects, crabs, shrimps)
SIPUNCULIDA (peanut worms)
ECHIUROIDEA (sausage-shaped marine worms)
MOLLUSCA (clams, snails, squid, octopus)
PHORONIDA (horseshoe worms)
BRACHIOPODA (lampshells)
ECTOPROCTA (moss animals)
CHAETOGNATHA (arrowworms)
POGONOPHORA (deep-sea worms)
ECHINODERMATA (starfish, sea urchins, sand dollars)
HEMICHORDATA (acorn worms)
UROCHORDATA (sea squirts)
CHORDATA (fish, reptiles, birds, mammals, amphibians)

Of these only CHORDATA is of interest to us.    Each phylum contains numerous classes and CHORDATA is no exception.
Phylum CHORDATA contains seven classes, namely:-

 

AGNATHA (jawless fish)
CHONDRICHTHYES (cartilaginous fish)
OSTEICHTHYES  (bony fish)
AMPHIBIA (amphibians)
REPTILIA  (reptiles)
AVES (birds)
MAMMALIA (mammals)

Of these, only MAMMALIA is of interest to us.    MAMMALIA is derived from the Latin word ‘mamma’ which means breast.    Mammals are mostly terrestrial (the exception being whales, dolphins, etc.).    They have fewer bones than reptiles and the teeth are of four well-defined types (incisors, canines, pre-molars and molars).  The heart has four chambers and mammals are homiothermic (warm-blooded).   Scales are modified as hairs and mammary glands of females secrete milk.    Within the class Mammalia there are 18 sub-classes, namely:-

PROTOTHERIA (monotremes, e.g. echidna)
MARSUPIALIA (marsupials, e.g. kangaroo)
CHIROPTERA (bats)
INSECTIVORA (insect eating mammals)
PRIMATES (primates)
EDENTATA (edentates, e.g. sloth)
PHOLIDOTA  (pangolins)
TUBULIDENTATA  (aardvarks)
RODENTIA (rodents, e.g. rat)
LAGOMORPHA (lagomorphs, e.g. rabbit)
CETACEA (cetaceans, e.g. whale)
CARNIVORA (carnivores, e.g. lion)
PINNIPEDIA (seals)
PROBOSCIDEA (elephants)
HYRACOIDEA (coneys, e.g. hyrax)
SIRENIA (sea-cows)
PERISSODACTYLA (herbivores, e.g. horse)
ARTIODACTYLA (herbivores, e.g. antelope)

Of these, only sub-class MARSUP1ALIA is of interest here.    MARSUPIALIA is derived from the Latin word marsupium which means pouch or bag.   The Australian section of sub-class MARSUPIALIA can be divided into four orders, namely:- 

DASYUROMOPHIA
PERAMELEMORPHIA
DIPROTODONTIA
NOTORYCTEMORPHIA

A more comprehensive list in part two of this article, gives details of all the Australian marsupials (and their common names).     This list places all species into their respective orders, families, sub-families and genera.     Subspecies and species which were extinct prior to the first arrival of Europeans will not be included.    Note however, that Taxonomy is not static.    As new species are discovered, and the relationships between known species become better understood, it is normal for species and even genera to be re-defined or re-named.

NOMENCLATURE 

As noted above, many taxa (particularly those of the METAPHYTA and METAZOA) have common names.    To eliminate the problems associated with the use of these common names, each species has one unique and internationally accepted scientific name.     This name is a Latin or latinised binomial (binomial = two part name).     The first part of the binomial is the generic name; that is, the name of the genus to which the species belongs. 

The generic name is usually one Latin or latinised word in the nominative singular case.    When written, the first letter is always capitalised.    The generic name is also set off from the rest of the written text by underlining or by the use of italics.     Thus, the species of grey kangaroos have scientific names with the generic name

 Macropus   (underlined)
 or
Macropus
   (italics)

The second part of the binomial is the specific name; that is, the name which distinguishes the different species in a genus.    The specific name is normally one Latin or latinised adjective which agrees grammatically with the generic name.     The first letter of the specific name should not be capitalised, although some of the older texts do when the name is derived from the names of persons or places.     Written specific names are always set off from the rest of the written text in the same manner as generic names.    Thus, the complete scientific name of the two species of grey kangaroos are:

Macropus giganteus
Macropus fuliginosus

or   using italics 

Macropus giganteus
Macropus fuliginosus
 

The same general procedure is used for subspecies names.  Thus, the six recognised subspecies of the two species of grey kangaroos (using italics) are :

Macropus giganteus giganteus
Macropus g. major
M. g. tasmaniensis
Macropus fuliginosus fuliginosus
Macropus f. melanops
M f. ocydromus
 

Note that in a list of scientific names like the preceding one where a particular generic name (or specific name when referring to a subspecies) is repeated several times, it may be abbreviated to its first letter for the second and subsequent names in the list.    However, this procedure must only be used for lists of scientific names and must never be used for lists of scientific names where there is a possibility of confusion between two or more generic names beginning with the same letter.

I hope this article has given you some insight into the procedure used, and the reasons for, the use of scientific names.

A list of indigenous Australian monotremes and marsupials follows:

Bennett's Wallaby
Juvenile NT Brushtail Possum
Swamp Wallaby
Golden Brushtail Possum
Red Kangaroos
Yellow-footed Rock-wallabies
Baby Squirrel Glider
Sugar Glider
Euro

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