Rodent

Rodents are a large group of mammals known for their continuously growing incisors, which they use for gnawing food and digging burrows. About 40% of all mammal species belong to the order Rodentia, making rodents one of the most diverse groups of animals on Earth. They live on every continent except Antarctica and have been introduced to many islands by human activity.

Most rodents are small, with robust bodies, short limbs, and long tails. They can be found in nearly every type of habitat, including forests, deserts, mountains, and even homes. Rodents have many different ways of living, from climbing trees to digging underground homes, and they often live in social groups with complex communication.

Rodents have been important to humans in many ways. Some are kept as pets, while others are used in scientific research. However, a few species, like the brown rat, black rat, and house mouse, are considered pests because they eat and spoil food and can spread diseases. Well-known rodents include mice, rats, squirrels, prairie dogs, porcupines, beavers, guinea pigs, and hamsters.

Characteristics

Rodents are known for their continuously growing, sharp incisors, which they must constantly wear down to prevent them from piercing their own skulls. These teeth have hard enamel on the front and softer dentine on the back, creating a sharp edge like a chisel. Most rodents have between 12 and 28 teeth, including a gap called a diastema between their front teeth and molars, which helps them handle food.

Rodents have strong muscles in their jaws that help them gnaw and chew. They use different methods to move around, such as walking, running, climbing, hopping, swimming, and even gliding. Some, like flying squirrels, can glide using special membranes. Rodents also have excellent senses of smell and hearing, and many have long, sensitive whiskers to feel their way. Many store food in cheek pouches to carry it back to their nests.

Distribution and habitat

Rodents live nearly everywhere, on every continent except Antarctica. They were the first land mammals to live in Australia and New Guinea without help from humans. Today, rodents can be found in many places because humans have taken them to remote islands.

Rodents adapt well to different environments, from cold tundra under snow to hot deserts. Some live in trees, others underground, and some stay near water. They also thrive where people live, like farms and cities. Rodents help nature in many ways. For example, by digging tunnels, they spread fungi spores, which helps plants grow. In North America's Great Plains, prairie dogs improve soil by aerating it, and beavers create wetlands by building dams.

Behavior and life history

Most rodents eat only plants, like grasses and leaves, while others also eat insects or small animals. For example, the field vole mainly eats plants but might occasionally eat insect larvae. Some rodents, like the African pouched rat, gather food in their large cheek pouches and sort through it later to eat the best parts.

Rodents can be social or solitary. Prairie dogs live in large groups, while hamsters often live alone. Some rodents, like beavers, live in family groups with parents and their young. Communication among rodents includes using smells, sounds, and even vibrations to talk to each other and warn of danger.

Many rodents form lasting pairs, while others have many mates. Mothers care for their young in different ways, depending on the species. Some rodent babies are born blind and hairless, while others are ready to move around shortly after birth. Overall, rodents are clever animals with good memory and learning abilities.

Evolutionary history

The earliest fossils showing the special teeth of rodents come from the Paleocene period, just after the dinosaurs went extinct 66 million years ago. These fossils were found in Laurasia, an ancient supercontinent that included what is now North America, Europe, and Asia. Rodents and their close relatives, the lagomorphs like rabbits, began to spread around the world during the Cenozoic era.

Some very early rodents lived in North America, and beavers first appeared there in the late Eocene. Over millions of years, rodents traveled to many parts of the world, even reaching places like Africa and South America by floating on natural debris. By about 20 million years ago, many modern rodent families existed. Some ancient rodents were much larger than today’s species, like Josephoartigasia monesi, which could be as long as 3 meters (10 feet).

Classification

Further information: List of rodents

Rodents are a large group of mammals known for their continuously growing incisors, or front teeth. The name "Rodentia" comes from a Latin word meaning "to gnaw." They are related to animals like hares, rabbits, and pikas, though rodents have only one set of upper incisors while lagomorphs have two.

Scientists have tried for many years to sort rodents into groups based on their physical traits. Different experts have suggested different ways to divide them, and even modern genetic studies have not fully settled the debate. Today, there are many families of rodents, with over 2,000 different species known to science.

Conservation

Some rodents face threats that put them at risk. Over 168 species need special care because people often don’t see them as important. Losing just a few species could mean losing many different kinds of rodents, since most groups have only one type of species.

Certain rodents have become a problem for birds on islands, like the black rat, which hurt many bird populations. However, efforts to remove these rats from islands have helped bird numbers grow again. Climate change has also been a big problem, especially for rodents living on small islands. The Bramble Cay melomys was the first mammal known to disappear because of human-caused climate change.

Interaction with humans

Humans have used rodents in many ways. Their fur has been used to make clothing. For example, Native people of North America used beaver pelts to make robes, and Europeans later valued this fur for making hats. Today, animals like coypu and chinchilla are also used for their fur.

Rodents are also a food source for many cultures. Guinea pigs have been eaten in South America for thousands of years, and in Peru, they are still a important source of protein. Other rodents like squirrels and porcupines are eaten in places such as the United States and by Native American groups like the Navajo and Paiute.

Rodents are also important in scientific research. Mice and rats are commonly used in laboratories because they are easy to care for and share many health conditions with humans. They help scientists study topics like genetics, diseases, and the immune system. Some rodents, like the Gambian pouched rat, have even been trained to detect diseases and dangers such as land mines.

Many rodent species are kept as pets because they are friendly, intelligent, and easy to care for. Pets such as rats, mice, hamsters, gerbils, guinea pigs, and chinchillas are popular choices in homes around the world.

However, some rodents can also cause problems. They eat large amounts of stored food, which can lead to big losses for farmers. They are also carriers of diseases that can spread to humans, such as bubonic plague and hantaviruses. Because of this, many communities work to control rodent populations using methods like traps, safe poisons, and even natural predators like cats.