How and why do we classify animals?
The seven main levels of classification are: Kingdom, Phylum, Class, Order, Family, Genus, Species. You also get subs of each category, such as sub-Class, sub-Order, sub-Family etc. We use this system to group animals that are alike and to know their genetic relationships through history.
The starting point of all classifications is the Kingdom. There are five groups at the Kingdom level which inform us as to what the thing we’re talking about is. The five Kingdom groups are: Monera, Protista, Fungi, Animalia, and Plantae. These groupings are based on whether the species is single-celled, multicellular, an animal or a plant, and a number of other characteristics that would determine this first level of grouping. The Kingdom grouping only had two groups previously, plants and animals; but as the field of research has developed and technology to see smaller organisms improved, some of these species didn’t fit into the original groupings which is why we now have five.
There are approximately 35 phyla (plural of phylum), the next grouping after kingdom. Each level of classification is used to specify even more features such as the phylum Chordata which includes all animals with backbones (vertebrates). This level really starts to segregate and organise the species. The number of species belonging to each phylum changes quite regularly as new species are found and more research on known species becomes more advanced.
Each level becomes larger and larger in number as we specify each animal, plant, single celled organism etc. To find an exact number past the phylum level proved rather difficult as each of those phyla are broken down to the different classes within them. This then breaks down to order and then family and so on. With an estimate of 8.7 million different species in the world, trying to find information on the exact number for all the different levels except for kingdom and phylum (the least specified levels) becomes rather challenging.
By understanding all the different groupings of every single species, we are then able to build something known as an Extant Phylogenetic Bracket (EPB). An EPB is a sort of tree of life, showing all the connections between every living thing. The full EPB is absolutely huge, but to give you an example of what a small section would look like, see the diagram below.
From the diagram, we can see that there are past ancestors that connect birds, non-avian dinosaurs, and crocodiles together by going back far enough. This gives a great understanding of evolution and relationships between different species.
When scientifically writing about an animal, we use what is known as its scientific name (also known as its binomial or taxonomic name). This is made up of the two categories Genus and Species. For example, if I were to write a paper about my favourite animal, the African leopard, I would also include its scientific name: Panthera pardus. The scientific name should always be written in italics, and only the Genus name has a capital letter at the start. The scientific name used to be referred to as the Latin name, however, more often than not now, the names include both Latin and Greek, and therefore it is more accurate to call it the scientific name.
For an example, let’s see what the full classification for the African leopard is.
So the Kingdom shows it is an animal, the phylum shows that it is a vertebrate (Chordata), the Class shows it is a mammal, the Order shows that it is a carnivore, and then the suborder indicates it is a feline, and the Family shows it is within the cat family.
Most of the classification, especially when scientists first started classifying everything, was done purely on an observation basis. The classification would be given due to physical characteristics. Nowadays, whilst observation is still used, genetics are also used to determine the exact lineage of each species. So, we know that the classification helps us link genetically similar animals together and therefore, can help when determining evolutionary lineages.
To keep in the same theme as the cat example, most big cats come under the Genus Panthera, however, a cheetah does not. The cheetah’s scientific name is Acinonyx jubatus, meaning that it is in a different Genus to other big cats. When we think of the physical characteristics of cheetahs compared with other big cats, we can understand why it has been identified in its own genus.
One of the biggest reasons we classify animals is so that species do not get confused. Most people know animals by their common name, such as leopard, or lion, or elephant for example. But in different countries, they may use a different common name because of their spoken language. The scientific name doesn’t change, regardless of the common name given in any country. Additional subspecies names are also given to differentiate that it may not be exactly the same species in different regions.
Another classification example:
This is an example for a Cape Buffalo – the Scientific name is Syncerus caffer. However, if we look at a subspecies such as the Forest buffalo, it keeps the Syncerus caffer, but you need to add nanus to the end. Thus, the full name of the forest buffalo is Syncerus caffer nanus.
For full classifications of animals, you can use Wikipedia, which is sometimes a good source of information if used carefully. For a more reliable source of this information, you can use the IUCN Red List, which is also what determines how endangered animals are.