Relatively speaking: How animals are classified
- Meghan McMahon
- Sep 26
- 4 min read
Have you ever been to a family party and thought, “Wow, how am I related to all these people?” You might be closely related to some, like your parents, and more distantly related to others.
We imagine early biologists were thinking the same thing! Are eagles related to cardinals? Beavers to muskrats? Coyotes to domestic dogs? If so, just how closely are they related?
While amateur naturalists came up with some ideas, it wasn’t until 1735 that Carolus Linnaeus, a Swedish botanist, first introduced his classification system. Because of this, he is known as the father of modern taxonomy, the science of naming and classifying organisms. The accepted system used by scientists all over the world today is based on this original system.
The classification system works in levels, or groups. The highest level, or largest group, contains the most organisms. The next level is broken up into smaller groups, the level below that is broken down further and this continues until you reach the species level.
Let’s use an example organism: the beaver.
The beaver is an animal, so it belongs to the kingdom animalia. All animals, including humans, belong to this level or group.
Next is the phylum. Touch your back and feel your spine. It moves with you and allows you to bend in all sorts of ways. That is a characteristic of the next group: Chordata. Chordata is a group that includes animals with a notochord, which is a flexible rod that supports the body.
Words to know
Biologist: A person who studies biology, which is the science of living organism.
Botanist: A person who studies plants.
Incisor: A narrow-edged tooth at the front of the mouth that is adapted for cutting.
Naturalist: A person who studies natural history.
Taxonomy: The branch of science concerned with classification of organisms.
Beavers are mammals, which mean they belong to the class Mammalia. Being mammals, they have fur, are warm blooded and have glands to feed their young.
The order beavers belong to is Rodentia. If you’re thinking that word looks a lot like “rodent,” you’re right! This largest group of mammals is distinguished by their incisors that never stop growing. What other animals can you think of that might belong to this order?
The family Castoridae is referred to as the beaver family because it contains the two living species of beaver, as well as fossil relatives. Yep, this system even includes animals that are extinct!
An animal’s genus is the first half of its scientific name. For beavers, it is Castor. This group contains the North American beaver, which you can find all over this continent, and the Eurasian beaver, which can be found across Europe and parts of Asia.
Finally, the specific species name for the North American beaver is canadensis.
Scientific names for any organism include the genus and species name. In the beaver’s case, its Castor canadensis. This helps scientists across the world know specifically what organism is being discussed.
Think of this as the animal’s first and last name. You wouldn’t just introduce yourself as your first name! There could be many people with your name out there. But combined with your last name, others know that name belongs to you specifically!
How do scientists categorize animals?
They use physical evidence. For example, we can see that beavers have long teeth like many other rodents. Scientists today also use genetic evidence, what we learn from an organism’s DNA. In general, the more taxa (levels or groups) an animal shares with another, the closer the two are related.
Why do we use this system?
This classification system helps explain how organisms are related (or not) and how close in relation they might be. The system has changed since 1735. The more we learn about specific organisms, the better we can organize them.
Speak like a scientist!
Why say “Rodentia” and not “rodent?” Or “Castor” instead of “beaver?” The unfamiliar names are not actually English words. They’re Latin. It’s a language that many scientists from centuries ago were familiar with when papers, guides and scientific studies were first written.
Fun fact: Many people all over the world speak languages that have roots in the Latin language. For example, “castor” is the Latin, Spanish and French word for “beaver!”
Even though each scientist has a common name for animals in their own language (example: beaver), when scientifically speaking, they will use the scientific name (example: Castor canadensis) to convey a clear message to others.
What is your favorite animal? What do you call it? How do scientists categorize it?
Another example!
Let’s try this again with another organism we see all the time in the preserves. Here are the first three taxonomic levels:
Ok, so Animalia kingdom lets us know it’s an animal. The phylum, Chordata, just like the beaver, tells us it has a backbone.
Any guesses yet?
This animal also is a mammal, although it doesn’t have as much hair as many other mammals. It also belongs to the class Primates. Whoa! Monkeys in the preserves? Not the ones you’re thinking of….
Did you guess humans? The scientific name for humans is Homo sapiens. Today there is only one species of humans, but a long, long time ago there used to be more.
Whichever species, we love to see humans out in the preserves enjoying all the organisms that belong to the other kingdoms, phyla, classes, orders, families and genera!
