The primary reason scientists place animals into group classifications is to arrange them into an order that makes studying animals easier.
Animals, as a whole, are each placed into one of six groups: mammals, reptiles, amphibians, birds, insects and fish. These groups of animals are broken down further into smaller and smaller categories according to their relationships, habits and physical characteristics.
The Order Rodentia
Inside the mammal category, there are groups called “orders”. The order of Rodentia is a hugely successful group of species that make up 40 percent of all the mammal species in the world. Rodentia is comprised of 29 families, 426 genera, and 1,814 species, making them the largest mammal group by a mile.
Rodents can be found in nearly every corner of the world, excluding New Zealand, Antarctica, and a few oceanic islands. They are found living in every habitat on the planet including; oceans, lakes, rainforest canopies, deserts, grasslands, woodlands, rocky mountains, and some rarely surface from underground.
As a whole, rodents are an active bunch and need to eat almost continually. Because food can be scarce in the winter months, some rodents go into hibernation to slow their metabolism down, making it possible for them to stay alive until food is plentiful again. Still others wake up periodically to take in a little nutrition.
The order of Rodentia is comprised of all mammal sizes. From the very smallest rodent, the pygmy jerboa (Salpingotus crassicauda) who weighs in at a mere 0.5 - 0.7 ounces to the largest rodent, the capybara (Hydrochaeris hydrochaeris) can weigh as much as 175 pounds.
Familiar Mammals Belonging to The Order of Rodentia:
- Mice
- Rats
- Squirrels
- Beavers
- Guinea pigs
- Marmots
- Mink
- Prairie dogs
- Gophers
- Lemmings
- Voles
- Porcupines
- Capybara
- Maras or Patagonian Cavies
* Rabbits and hares do not belong to the order rodentia, but instead belong to a class all their own.
Criteria For Rodentia Classification
A characterization all rodents have is a mere two incisors (gnawing teeth) in the upper jaw and two in the lower jaw. There is a distinct space in between these incisors and the grinding teeth in the back of both upper and lower jaws.
These front incisors are special in the fact that they have hard enamel on the front of them, however, the back of the teeth lack the enamel and are softer. The rodent’s special incisors make the rodent need to gnaw almost continually. Gnawing isn’t the same thing as chewing.
Gnawing is when the animal shaves off layers of wood, food or another pliable object and this wears away some of the incisor’s growth. Chewing refers to the grinding that's done with the back teeth. Because the backs of the incisors wear away due to the animal's constant gnawing, the front teeth are able to maintain a chisel-type edge.
Rodents’ incisors continue to grow their entire lives, so these animals need to gnaw on wood or other pliable objects to wear them down or the teeth could grow so long that the mammal will be unable to eat. If the lower jaw is misaligned, the teeth may not wear down properly and can literally grow into the rodent’s upper skull.
Not every rodent, but most, meet the last criteria of rodentia. That is, they primarily have four toes on each front foot and five toes on the back feet. Also, a large portion of rodents are nocturnal (active at night). The squirrel is the most obvious exception to that rule.
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