Animal Classification: A Taxonomy for All Living Things

Gray Wolf jumping over log in autumn — Everything in this photo, from the wolf to the fallen tree it's jumping over, can be classified using the same taxonomy. Stan Tekiela Author / Naturalist / Getty Images

You can categorize every single living being. This classification system allows scientists to study plant and animal diversity and to group closely related species. From horses to insects to worms, animal classification focuses on every animal in the so-called kingdom animalia.

In this article, we'll take a closer look at the origins of this classification and how animal classification works.

Origins of Animal Classification

Though it has changed throughout the years, you can thank Swedish botanist and zoologist Carl Linnaeus for creating a taxonomy to categorize all living beings. In 1735, he introduced this system in "Systema Naturae," an 11-page pamphlet. Linnaeus summarized his work as "God created, Linnaeus organized."

He was not the first to attempt to make sense of all life forms. Aristotle looked at animals through ethnology, physiology and anatomy. Theophrastus categorized plants by the way they originated. And Pliny the Elder also gave it a go.

"There were different systems in use at the time," said Janis Sacco, the former director of exhibitions at Harvard Museum of Science & Culture, to The Harvard Gazette. "Some were ecological, based on the idea that organisms that existed in the same habitat must be related to one another. Linnaeus believed that there should be a regular, systematic way of identifying what something is by comparing it to something else."

The Five Kingdoms

Kingdom follows domain — the largest classification in biology also known as dominion, empire or superkingdom. Each kingdom encompasses many living beings.

Linnaeus originally identified three kingdoms when he introduced "Systema Naturae": Regnum Amimale (animals), Regnum Vegetabile (plants) and Regnum Lapideum (minerals).

Today, we classify living things according to five kingdoms:

Animalia: Also known as the animal kingdom, this includes species that are multicellular and eukaryotic (anything that contains a nucleus). Unlike plants, animals eat food for energy.
Fungi: The fungi kingdom includes multicellular species with organelles and a cell wall. They do not have chloroplasts. Chanterelle, penny bun and fly agaric belong to this kingdom.
Monera: These single-celled organisms have a cell wall, but they do not have organelles, chloroplasts or a nucleus. You will find bacteria in this kingdom.
Plantae: The kingdom is where plants belong. Plants are multicellular, and have organelles and chloroplasts.
Protista: These are single-celled organisms that have organelles and may have a cell wall and chloroplasts.

Animal Species Classification

Each living organism falls under eight categories. At the very top, there's the broadest category (domain), and each subsequent level gets more focused. Here is the system to follow for classifying animals:

Domain: There are three domains: Archaea, Bacteria and Eukarya. Animals belong to the latter group.
Kingdom: There are five kingdoms: animalia, fungi, monera, plantae and protista. Every and any animal belongs to the animalia kingdom, including marine life, snakes and lizards.
Phylum: There are dozens of other animal phyla that we don't have listed here, but most animals fall within a handful of categories, including arthopoda (millipedes, spiders and crayfish), cnidaria (corals, jellyfish and hydras), chordata (humans and dogs), mollusca (slugs, snails and chitons), nematoda (threadworms, hookworms, and whipworms) and porifera (sponges and other invertebrate animals).
Class: Each of the animal phyla divides into smaller groups. For example, the phylum chordata, which encompasses all vertebrates, has a few different classes like amphibians, birds, fish, reptiles, and mammals.
Order: If you look at the class mammalia, you will find several orders, such as carnivora, primates and rodentia.
Family: Within carnivora, or animals that share eating meat in common, there are 13 distinct families, according to Animal Diversity Web. These include Ursidae (bears), Felidae (cats) and Canidae (dogs).
Genus: Within genus, there are even smaller categories. For example, within the Ursidae family, there are five genera: Ailuropoda (giant panda), Helarctos (sun bear), Melursus (sloth bear), Tremarctos (spectacled bear) and Ursus (black bear, brown bear and polar bear)
Species: Within the Ursus genus, there are four species, identified through their scientific names: Ursus americanus (American black bear), Ursus arctos (brown bear), Ursus maritimus (polar bear) and Ursus thibetanus (Asiatic black bear).

Some taxonomies account for nine categories, with suborder falling between order and family.

Species Name

Species names are a combination of genus and species, with the first word capitalized and the second one written in lowercase.

Linnaeus created this binomial nomenclature to replace an ununiform naming convention, where some animals could have a short two-word name and other animals could have a longer phrase.

Examples of Animal Classifications

Here are a few examples of animal classifications.

Blue Whale (Balaenoptera musculus)

Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Family: Balaenidae
Genus: Balaenoptera
Species: musculus

Gray Wolf (Canis lupus)

Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Canidae
Genus: Canis
Species: lupus

Humans (Homo sapiens)

Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Hominidae
Genus: Homo
Species: sapiens