Zoology: Facts

Two Giraffes

The world is full of living things, both plants and animals. Zoology is the study of the animals of the world, or what is scientifically known as the animal kingdom. The animal kingdom includes humans, bears, bumblebees, ants, goldfish, clams and even a particular single-celled life known as protozoa. An animal is defined as anything that has a specific shape, grows, can move on its own, hunts for food, has sensory and nervous systems and responds to its environment.

Classification of Animals

Two Dogs

Before we head into a full understanding of animals, we need to understand how science names animals. Scientists from all over the world study animals. Because the scientists speak various languages, the names of all animals are based on an old language known as Latin. A man by the name of Carolus Linnaeus established this method of naming animals back in the 1750s. Learn more about Linnaeus’ life at Famous Scientists.

Animals are grouped, or classified, into separate categories based on physical traits. All animals belong to the kingdom of “Animalia.” The next category is their phylum, then class, then order, etc. This classifying process continues by sorting animals into additional groups with more specific similar physical traits.

Classification categories look like this:


Humans would be classified in this way:


Scientists often refer to an animal by the genus and species only. For this reason humans are often referred to as homo sapiens. By the time it gets down to species, we are usually talking about the same animal, but with different coloring or other physical and even sometimes behavioral traits. For example, which kind of bear, which kind of dog, or which kind of owl. Not all animal genera (plural of genus) have more than one species.

Vertebrates or Invertebrates

Starting with the animal kingdom, or Animalia, and working down the classification ladder, the next step divides animals further into major groups or what is scientifically known as phylum. These phyla (plural of phylum) are made up of vertebrates and invertebrates – or those with backbones (vertebrates) and those without (invertebrates). Vertebrates make up just one of the approximately 30 different phyla in the animal kingdom. All the rest are invertebrates.


Fish Skeleton

Vertebrates are the animals that have a backbone. But more specifically, they have skeletons; bones that are the structure of their bodies. A skeleton gives the animal support, strength and shape. For additional information on skeleton’s you might want to visit Science Trek’s site titled Skeletons.

The backbone is the section of the skeleton that runs down the middle of the back. Nerves from the brain are sheltered within the backbone – also called the spine. These nerves control the movements and the ability to feel throughout the body. They help sense temperature, pain, tickling, touch, and all of the other senses like smell, taste, sound, and sight.

Vertebrates are divided further into five smaller groups. Each of these groupings are known as a class. Again, these classes are based on physical characteristics. The five classes of vertebrates are mammals, fish, birds, amphibians, and reptiles. Let’s explore the details that separate each of these five classes.



  • Have live births (except the platypus and the echidna)
  • Feed their young with milk
  • Have hair or fur
  • Breathe with lungs
  • Warm-blooded
  • Examples: human, dog, bear, horse, elephant, dolphin

Clown Fish


  • Live almost always in water –  although some can survive short periods out of water
  • Have gills
  • Most have scales
  • Cold-blooded
  • Lay eggs
  • Examples: salmon, trout, goldfish, tuna, clownfish

Hummingbird at Flower


  • Have feathers
  • Have scales on their legs
  • Have wings – although not all birds fly
  • Lay eggs
  • Breathe with lungs
  • Have beaks or bills
  • Warm-blooded
  • Examples: eagle, chicken, ostrich, penguin, bluebird, hummingbird



  • Live part time in water and part time on land
  • Need moisture for their skin
  • Lay eggs
  • Go through metamorphosis - gills for part of their lives
  • Cold-blooded
  • Can breathe and drink through their skin
  • Examples: frog, toad, salamander, newt



  • Have scales or plates
  • Most lay eggs, a few have live births
  • Cold-blooded
  • Breathe with lungs
  • Examples: alligator, crocodile, turtle, iguana, snake, Komodo dragon


Lobster on a Rock

While vertebrates have a backbone, invertebrates do not. There are many phyla of invertebrates, each being grouped according to their physical traits. Not everyone agrees about the names of the different animal phyla or even how many invertebrate phyla categories there are. Scientists are constantly finding new life forms on the earth and have to restructure the classification system to accommodate the new animals. Because there are so many different phyla of invertebrates, classifying them gets complicated.

Invertebrates have other physical traits that make up for the lack of a skeleton. Some have an outer shell that protects them – like the clam. Some have bodies with an armor-like structure on the outside known as an exoskeleton – like a lobster. Some have neither of these and are just soft tissue, but then they live in environments that this quality is actually a benefit – like a jellyfish.

Ants Marching

Invertebrates make up about 95% of all of the earth’s animals. All invertebrates are cold-blooded. Invertebrates include: starfish, crabs, sea anemone, clams, oysters, coral, jellyfish, sand dollars, sponges, squid, octopus, lobsters, lady bugs, mosquitoes, bees, butterflies, ants, grasshoppers, spiders, centipedes, earthworms, and snails. These are just a few of the many, many, many animals that are called invertebrates.

Cold-Blooded or Warm- Blooded

Panting Dog

All animals are either warm-blooded or cold-blooded. Warm-blooded animals can regulate their own body temperature. They convert the food they eat into energy to stay warm. They shiver when cold and seek shelter to increase their comfort. When hot, they sweat or pant to cool themselves. Some animals even migrate when the seasons change to find more comfortable accommodations.

Cold-blooded animals do not generate their own heat, but must take on the temperature of their environment. They may go and lay in the warm sun to heat themselves or burrow into the soil to find cooler shelter. Hibernation, special blood chemicals, and crowding together to conserve heat are also ways that different cold-blooded animals can heat themselves. Cold-blooded animals tend to be more active in warm environments and slow moving in cold surroundings.

Herbivores, Carnivores, Omnivores


What animals eat is also crucial to their classification. They are grouped into three distinct categories: herbivores, carnivores, and omnivores.

Herbivores – eat just plants. Herbivores are also known as primary consumers because they are near the beginning of the food chain and food web. (See Science Trek’s site on Food Webs.) They get all of their food from plants. They can range in size from very tiny insects to huge animals such as elephants. Some herbivores will eat any part of a plant, while others stick to a special portion of a plant like just the fruit, just the leaves, just the roots or just the bark. Some herbivores will eat from only one or two types of plants, while others will eat anything that grows. Herbivores graze from plant to plant and often eat constantly in order to obtain enough nutrition to survive. Some herbivores have special prehensile lips, tongues, tails or trunks that can grab their food like the fingers on a person’s hand. Some herbivores have special stomachs that have multiple chambers that store the grasses or leaves until later when they partially regurgitate the food and chew it before passing it to other chambers for final digestion. (See Science Trek’s site on digestion.) Since herbivores chew their food they need to have flat molars for crushing and grinding the leaves, seeds, and grasses that they eat.

Tiger Eating

Carnivores – eat just animals. Carnivores are hunters that often look for animals smaller than themselves as prey. They are known as the secondary consumers because they eat the primary consumers. They usually have powerful jaws that allow them to grasp their prey using their mouths. These animals have pointed teeth for grabbing and tearing their food. Most of these animals do not chew, but rather swallow their food whole or in chunks and allow their digestive system to process the food from beginning to end. For this reason, they have a single chamber stomach. Most carnivores also have claws or in the case of birds they have talons. This is for grabbing their prey. Carnivores help keep the populations of other animals controlled so that they don’t grow larger than their food supply will allow.

Carnivore Jaw

Omnivores – eat both plants and animals. Omnivores can, and do, eat both plants and animals. They are also secondary consumers. They have both types of teeth – the pointy, tearing teeth and the back grinding molars. Claws are not a requirement for omnivores, although some do have claws. Omnivores have simple, one-chambered stomachs. Omnivores are the most likely of the animals to survive extreme environmental situations because they can alter their food choices to fit the circumstances. They will eat any food that becomes available depending on season, weather, drought, famine, or other challenge. Some omnivores will even scavenge food and garbage.

Unusual Animals That Cross Boundaries


Scientists don’t know why, but there are some animals that don’t stick to the rules of classification. Just take the duck-billed platypus, for example. The platypus is technically a mammal that lives in Tasmania and Eastern Australia. It has most of the traits that other mammals exhibit, but it lays eggs rather than giving birth to live baby platypuses. (Yes, platypuses is the correct plural form of platypus). It also has traits that seem to be like other, unrelated animals. It has webbed feet with claws, a duck bill, the body of an otter, and the tail of a beaver. The male platypus is also venomous with stingers on the hind feet that can jab an enemy. 


The echidna (ə'kid-nə) which also lives in Tasmania and Australia, is a spiny looking anteater that also lays eggs. You might want to read more about it from the San Diego Zoo. These two animals are the only mammals known to lay eggs.

Another unique animal is the elysia chlorotica. It is a sea slug that lives off the eastern coast of North America. While it is an animal, it is also able to produce its own food in much the same way as a plant does. It uses sunlight in combination with chlorophyll to create food inside its own body. The elysia chlorotica can do this because it sucks the chlorophyll from algae and somehow keeps the chlorophyll alive and useful in its own body. It is also able to eat food like all other animals do, but has this plant-like behavior for when food is scarce.

Sea Slug in the Water
 Elysia chlorotica - Image courtesy of  Nicholas E. Curtis
 and Ray Martinez, University of South  Florida

The shark is a fish, but some species do not lay eggs. Some species of shark give birth similar to a mammal. They do not take care of their young (called pups), but leave them to survive on their own. Sharks although considered a vertebrate, do not have skeletons of bone. Instead they have a jaw of bone and the rest of their skeleton is made of cartilage. Cartilage is the stiff material that is found in the end of your nose and in the outer ear.

Here are links to some other strange creatures found on the earth. Many just don’t quite fit their classifications.

Axolotl is an aquatic salamander that never grows past its larvae stage and can regrow a lost or damaged leg.

A Group of Capybara

The capybara is a very large, semi-aquatic rodent. They live in Central and South America. They have webbed feet and can actually stay underwater for up to five minutes.

Hagfish is an eel-like fish that can tie itself into a knot. It is a very slimy critter with a partial skull but no skeleton.

Blobfish is a grumpy looking fish that doesn’t hunt, but waits for food to swim by. It doesn’t have a gas bladder which most fish have to keep them buoyant. Instead it is made of a gelatinous material that keeps it afloat. They have no muscles so they simply float in one place.

Blobfish - Image courtesy of NOAA Alaska Fisheries Science Center

Find more ocean creatures of an unusual nature at NOAA (National Oceanic and Atmospheric Administration).

Australia has some of the most unique animals in the world. Many are found nowhere else on the earth. Check out Panique to learn more about the rare creatures found in Australia.

Zoology Fascinating Facts


  • There are more chickens than people in the world.
  • The blue whale makes the loudest sound of any other animal.
  • A rhinoceros horn is made of compacted hair.
  • Only female mosquitoes bite.
  • The Asian Goose flies the highest – right over the Himalaya Mountains.
  • There are at least 900 thousand species of insects in the world.
  • In the U.S. 23 states have a butterfly as their state insect.
  • The cheetah can run the fastest of any animal.

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