Animal Classification: A Kid's Guide to Understanding the Animal Kingdom

The animal kingdom is vast and diverse, filled with creatures of all shapes and sizes. The animal classification concept helps kids understand how scientists make sense of the animal kingdom by naming and grouping species. But how do scientists organize and make sense of this incredible variety? This article will explore the fascinating world of animal classification, making it easy for kids to understand how scientists group animals based on their similarities and differences.

What is Animal Classification?

Animal classification is how scientists organize animals into groups and sort them by what they have in common. Putting animals in order like this is called taxonomy. This makes it easier for scientists to study animals and understand how living things are related. For an example: A whale and a dog don’t have as much in common, but a dog and a wolf do.

Back in the 18th century, a Swedish man named Carolus Linnaeus thought it was important to organize living things, and he developed a system to do just that. He started out interested in plants, but he ended up ordering all life as he knew it. We still use the essence of his system today. Scientists are constantly refining the system based on new knowledge. Who knows?

The Linnaean System

The classification system commonly used today is based on the Linnaean system and has eight levels of taxa. Generally, scientists agree there are six kingdoms. The animal kingdom (called Kingdom Animalia) is just one of those. In case you’re interested, the others are Achaebacteria, Eubacteria, Protists, Fungi and Plants. Originally, Linnaeus only identified two kingdoms: plant and animal.

Levels of Classification

Every animal on the planet, down to the most microscopic creature you can imagine, can be classified according to this system. You can remember the order the system comes in with one of the following phrases. The first letter of each word is the first letter of the level of classification. These levels start out broadly - that means the top levels have the most animals, and they get narrower and narrower as you go down. So, by the time you get to the species, there is only one animal in the group. From the most general to the most specific, these are domain, kingdom, phylum (plural, phyla), class, order, family, genus (plural, genera), and species. (For plants and fungi, the term division is used interchangeably with phylum.) Each level is contained, or nested, within the level above it. For example, a genus contains one or more species; a family contains one or more genera; an order contains one or more families; and so on. The domain is the highest level of organization and is the largest group.

Domain: The highest rank in biological classification. There are three domains-Archaea, Bacteria, and Eukarya.
Kingdom: Each domain is divided into kingdoms. Eukarya is divided into Animalia (animals), Plantae (plants), Fungi (mushrooms, molds, and yeasts), and several kingdoms of protists. The domains Bacteria and Archaea are also divided into multiple kingdoms.
Phylum: The phylum ranks below the kingdom and above the class in taxonomy. Scientists use the term phylum for all species, and the term division can be used instead of phylum for plants and fungi. Organisms are classified in a phylum or division based largely on general body plan. For example, members of the Phylum Chordata have an internal skeleton and a backbone or notochord (a primitive backbone).
Class: The class ranks below the phylum and above the order in taxonomy. Members of a class share more characteristics with each other than they do with other organisms in the same phylum.
Order: The order ranks below the class and above the family in the taxonomic hierarchy. The groups in an order have more in common with each other than they do with other members of the same class.
Family: In taxonomy, the family ranks below the order and above the genus. Members of the same taxonomic family are more closely related to each other than they are to other members of the same order.
Genus: The genus is the taxonomic rank between family and species. The groups of organisms in a genus share many structural similarities and are very closely related. Members of a genus are more closely related to each other than they are to other genera in the same family.
Species: The species is the most fundamental unit in taxonomy and ranks at the base of the biological classification hierarchy. Members of the same species share the same evolutionary history and are more closely related to each other than they are to any other organisms, including other members of the same genus.

Naming Animals: Scientific Names

Scientists use an internationally accepted system for classifying and naming organisms. The Linnaean system assigns each species a two-part scientific name composed of Greek or Latin words. The first part of the scientific name is the organism’s genus, a taxon that includes closely related species. The second part of the scientific name is called the species name, and it is particular to each species in the genus. The species name is always written in lowercase and italicized. Together, the genus name and the species name comprise the scientific name of the species. The two-part scientific name is sometimes called a binomial-from the Latin words bi-, meaning two, and nomen, meaning name.

Using scientific names helps scientists avoid the confusion that can arise when referring to an organism by its common, or everyday, name.

Vertebrates and Invertebrates

One of the first ways to classify animals is by sorting them into two main groups: vertebrates and invertebrates.

Vertebrates: Animals with Backbones

Vertebrates are animals that have a backbone or spinal column. This group includes many familiar animals, such as:

Mammals (like humans, dogs, and whales)
Birds (like eagles, penguins, and parrots)
Fish (like sharks, salmon, and goldfish)
Reptiles (like snakes, turtles, and lizards)
Amphibians (like frogs, salamanders, and toads)

Invertebrates: Animals Without Backbones

Invertebrates are animals that do not have a backbone. This is a much larger group than vertebrates and includes a huge variety of creatures, such as:

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Insects (like ants, butterflies, and beetles)
Arachnids (like spiders and scorpions)
Mollusks (like snails, clams, and squid)
Worms (like earthworms and tapeworms)
Jellyfish

Six Basic Classifications

Within the vertebrate group, animals can be further sorted into six basic classifications: mammal, bird, fish, reptile, amphibian, and insect.

Mammals

Mammals are warm-blooded vertebrates that have hair or fur, give birth to live young (with a few exceptions), and feed their babies milk. A cow, for example, is a vertebrate because vertebrates have backbones and the cow has a backbone. A cow has fur, has hooves, has udders, produces milk, has hair (fur) on body and is warm-blooded.

Birds

Birds are warm-blooded vertebrates that have feathers, wings, and lay eggs.

Fish

Fish are cold-blooded vertebrates that live in water and have gills for breathing.

Reptiles

Reptiles are cold-blooded vertebrates that have dry, scaly skin and lay eggs.

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Amphibians

Amphibians are cold-blooded vertebrates that live part of their lives in water and part on land. They have smooth, moist skin and lay their eggs in water.

Insects

Insects are invertebrates with a three-part body (head, thorax, and abdomen), six legs, and usually wings.

Changes in Classification Systems

In Linnaeus’s time, scientists characterized organisms as either plants or animals. Linnaeus followed this general rule, dividing all living things into two kingdoms-the Kingdom Plantae (plants) and the Kingdom Animalia (animals). His system was later modified by other scientists, especially as advances in microscopes revealed key differences among organisms at the cellular level. For example, Linnaeus classified fungi and algae in the plant kingdom.

Over time, the Linnaean classification system was expanded, first to three kingdoms and then to four. By the 1960s scientists had organized living things into five kingdoms-the Monera (bacteria), Protista (protozoa and algae), Fungi (mushrooms, yeasts, and molds), Plantae (plants), and Animalia (animals). In the late 1970s American microbiologist Carl Woese reported on several key genetic differences he had observed in prokaryotes. The new prokaryotes he had discovered, the Archaea, were so different from previously known bacteria that he and other scientists proposed a new, top-level taxon-the domain. The three-domain system is the standard classification system that has been used by scientists since the 1990s. However, many schools still teach a simplified system to introduce younger students to the idea of classification.

Activities for Learning Animal Classification

There are many fun and engaging activities to help kids learn about animal classification.

Sorting Animals: Without telling students why you are sorting, begin to place the animal pictures into two groups (vertebrate and invertebrate) on your pocket chart. Ask students to try to guess the rule for how you are sorting the animal pictures. Introduce the words “vertebrate” (animals with backbones) and “invertebrate” (animals without backbones). Ask students, “Why would we ever want to sort animals into different groups?” If needed, offer the idea that sorting animals can help us understand how living things are related.
"Animal Classification Toothy" Game: Students will answer animal classification questions on printed or digital task cards. Next, they choose the correct answer from three choices. If the answer is correct, a tooth is placed in the Toothy character’s mouth. If the answer is not correct, they go back to the question to try again.
Animal Classification Worksheet: These Animal Classification worksheet pages are a great way for children of all ages to practice and improve their knowledge of animals as well as work on their fine motor skills. In these classifying animals worksheet, chidlren will cut and paste the animals into the correct columns. This animal classification for kids activity is perfect for first grade, 2nd grade, 3rd grade, 4th grade, 5th grade, and 6th graders too.

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