All living organisms are classified based on basic, shared characteristics. Organisms within each group are then further divided into smaller groups. These smaller groups are based on more detailed similarities within each larger group. This grouping system makes it easier for scientists to study certain groups of organisms. Characteristics such as appearance, reproduction, mobility, and functionality are just a few ways in which living organisms are grouped together. The Australian Museum specialises in taxonomic and systematic research. Taxonomy and systematics comprise the describing, naming and classifying of plants and animals, and studying their origins and interrelationships. This type of research is essential for environmental assessments. It forms the basic building blocks of the study of nature, and is a key science on which many others depend.
Blue Butterflies are Morpho spp. from Brazil, belong to the largest family of butterflies, Nymphalidae, with more than 6,000 species distributed throughout most of the world. The orange and yellow butterflies are in the family Pieridae (whites, yellows and sulphurs), and come from Brazil, Peru, Malaysia and Indonesia. The colours in these species are from pigments (in contrast to the blue in Morpho.) The series of specimens set upside down are the jewelled Nawab Polyura delphis. These specimens come from Malaysia, but the species is also found in India. Image: Stuart Humphreys
Taxonomists classify all organisms into a hierarchy, and give them standardised names, that are often Latin or Greek, or derived from other languages and even people's names.These specialised groups are collectively called the classification of living things. There are seven main levels of classification in the hierarchy. They are, from the most to the least inclusive: Kingdoms is the most basic classification of living things. Currently there are five kingdoms-Animal, Plant, Fungi, Protist and Monera (unicellular). Living things are placed into certain kingdoms based on how they obtain their food, the types of cells that make up their body, and the number of cells they contain. Phylum is the next level following kingdom in the classification of living things. It is an attempt to find physical similarities among organisms within a kingdom. These physical similarities suggest that there is a common ancestry among those organisms in a particular phylum. Classes are way to further divide organisms of a phylum. Organisms of a class have even more in common than those in an entire phylum. Order Organisms in each class are further broken down into orders. A taxonomy key is used to determine to which order an organism belongs. A taxonomy key is a checklist of characteristics that determines how organisms are grouped together. Families Orders are divided into families. Organisms within a family have more in common than with organisms in any classification level above it. Because they share so much in common, organisms of a family are said to be related to each other. Genus is a way to describe the generic name for an organism. The genus classification is very specific so there are fewer organisms within each one. For this reason, there are a lot of different genera among both animals and plants. When using taxonomy to name an organism, the genus is used to determine the first part of its two-part name. Species are as specific as you can get. It is the lowest and most strict level of classification of living things. The main criteria for an organism to be placed in a particular species is the ability to breed with other organisms of that same species. The species of an organism determines the second part of its two-part name.
The taxonomic system for the hierarchical (ranked) classification of living organisms (and initially also of rocks, but that failed) is very simple. Organisms are assigned into different groups based on their characteristics, and these groups are hierarchical. The figure below shows the seven main types of groups. Kingdom is “higher” than phylum, while class is “lower”, and so on. For some, but not all groups there are subdivisions of these group types, such as subclass (subdivision within a class), infraorder (subdivision within a suborder; i.e. infra- is “below” sub-), and grouping of groups – e.g. superorder (group of orders). Since the system is hierarchical, organisms belonging
to the same class also belong to the same phylum and kingdom. For instance, all
animals belonging to the class Reptilia (reptiles, then) also belong to the
phylum Chordata (animals with a notochord, or backbone) and the kingdom
Animalia (animals). Now, the order Primates (primates), although belonging to the class Mammalia instead of Reptilia, also belongs to the phylum Chordata and kingdom Animalia. This might complicate things, but it is simply due to that the two classes Reptilia and Mammalia both belong to the same phylum and (therefore) kingdom. Notice that the name of the class is written with a capital first letter when you refer to the actual group. If you instead write “carnivorans” (belonging to the mammalian order Carnivora; not equal to “carnivore”, which refers to a feeding strategy, not a taxonomic group), you are really referring to the members of the group, and you do not use capital letters. This rule is useful for distinguishing between, for example, Primates and primates. While on the subject of formal rules, the genus and
species are special. First, both are always written in italics. Always. Second, the genus name is written with capital
first letter, but the species never has a capital. Third, you may refer to the
genus alone, e.g. Tyrannosaurus, but
never ever write only the species name. Never. This is because there may be
several different species with the same name, (for instance, they may be named
after the same discoverer) but they never belong to the same genus (if they do,
they are simply not allowed to have the same species name). In this way, we get
an endless variety of specific names for an endless variety of species.
Finally, you may shorten the genus name to only the first letter (capital)
followed by a dot and the species name (if you do not include the species name,
you may not shorten the genus name – it is silly to write something like “T. had remarkably short arms”). For
example, we take the genus Tyrannosaurus
(species name is excluded, since I refer to the genus), which has one species: Tyrannosaurus rex – although some
researchers argue that Tarbosaurus bataar
really belongs to Tyrannosaurus; in
that case, we would also have Tyrannosaurus
bataar (the species name is the
same, but is assigned to a different genus). Notice that I should not shorten
the genus name here, since it may be unclear what I mean by T. bataar.
Names can be discarded, usually by showing that two very similar species actually are the same, in which case the name given first is the one retained. Rejected names are written within quotation marks, and never italicised. A classical example is that "Brontosaurus exelsus" and Apatosaurus ajax were shown to be the same species (and therefore also belonged to one and the same genus); Apatosaurus, being the first to have been described and named, was kept. Another notable convention is that families tend to end with -idea, superfamilies with -oidea and subfamilies with -inae (their members would then be -ids, -oids, and -ines, respectively). For example, we have the Hadrosauroidea (superfamily), Hadrosauridae (family) and Hadrosaurinae (subfamily). Nowadays, the taxonomic system has been overshadowed by phylogenetic systematics, or cladistics. Cladistics is favoured because it systematically investigates evolutionary relationships, rather than just putting the organisms into different groups; cladistics tries to work out how they evolved, and how closely related different organisms are. Taxonomy, on the other hand, merely groups similar-looking organisms together in order to make some sense of the overwhelming chaos of life we have out there. The groupings can differ quite a lot between taxonomy and cladistics, since cladistics has a predilection for groups that include all the descendants within an evolutionary line (i.e. monophyletic clades). Therefore, cladistics disregards the group Reptilia, as it does not include birds (class Aves) and mammals, both which have their origins in the reptilian evolutionary line. Instead, cladistics just group them all together as Amniota. |
If two organisms are in the same phylum, they must also be in the same what classification and why
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