What are Rodents?

Rodents (scientific name: Glires) is an evolutionary branch that includes rodents and lagomorphs (rabbit, hare and pika). Rodent (niè ch) animal, English name rodent, this noun comes from the Latin meaning of "biting things". Refers to Rodents.

The assumed relationship in the primate is as follows:

Primate
Rodents		Primate
Rodents	Lagomorpha	Tree shrew	Primate
			Hydroptera	More monkeys	Primate

Rodents differ from other mammals in that they have two pairs of incisors--one upper incisor and one lower incisor.

Rodents are found all over the world. For example, mice live in all but Antarctica

Almost every rodent has its own

Most rodents are active at night or dawn, but there are also many types of day activities. Winter activity generally decreases, before the winter arrives, or store fat in the body

The origin of rodents has been an unsolved problem for many years.

• North America says

Paramys atavus fossil found the latest in North America 55 million years ago

Rodents and rabbits are very successful evolutionary groups in mammals, but most of them are harmful to human development. If human beings don't cherish or care for their living environment, maybe the earth will be their world after a few years. This is not alarmist, because these animals are extremely fertile and adapt to the environment.

According to the structure of teeth and masseter rodents, rodents are roughly divided into 4 categories: first rodents (now only one species in North America-mountain beavers), squirrels (including squirrels and beavers), and rodents (house rats, hamsters and jumping Rats) and guinea pigs (guinea pigs and capybara). Studies in molecular biology suggest that the similarity between South American guinea pigs and other rodents is lower than that of primates or other mammals. Therefore, South American guinea pigs are not considered to be rodents, thus challenging the traditional rodent concept.

Protozoa proliferated in the Paleogene period, and were basically extinct when the Oligocene Earth suddenly cooled. After the discontinuity, some living families appeared, such as beavers, squirrels, jumping rats and South American guinea pigs. The hamster family is the largest, and it includes several major categories (subfamilies) such as hamsters, mice and voles. The most primitive is the hamster, which was found nearly 40 million years ago in the Eocene and flourished in the Oligocene and Miocene. When 15 million years ago, its descendant, the rat, was gradually replaced. . There are about 120 genera and nearly 530 species in the subfamily Mouse, and only 7 genera and 18 species in the subfamily Hamster. The voles subfamily is another descendant of the hamster, which appeared about 5 million years ago.

Tooth evolution and stratigraphic division

Tooth is the main basis for studying the evolution of rodents and reliable evidence for stratigraphic division and stratigraphic contrast. The evolution of rodents is fast and changes in the structure of teeth are also fast. This is a favorable condition for identification and division of strata. For example, the earliest hamster fossils were discovered or originated in the Late Eocene strata in China, 37 million years ago, to the late Miocene, 10 million years ago. Hamsters have undergone three major substitutions. Each generation has its own structural characteristics, and there are many fossil representatives, which provide a very important scientific basis for stratigraphic division. The faster the evolution and the faster the variation of structural features, the finer and more precise the stratigraphic division may be. A type of voles called Moles, in less than 3 million years, teeth have roots to no roots, and the texture of the tooth surface has gradually changed. If you find a model mouse in the formation, you can infer the age of the formation.

Evolution of masticatory muscles

From the original starting rodent model, the masticatory muscles of rodents have evolved and developed in at least three different ways.

1. In the squirrel-type mode, the starting point of the lateral masticatory muscle moves forward to the front of the zygomatic arch of the maxillary condylar part. The maxillary condyle is enlarged and discoid. This method is common in squirrel-type suborders.

2. The porcupine pattern moved from the front of the maxillary condyle out of the maxillary condyle and became very large. Through the enlarged inferior frame hole, some starting points in front of the maxillary condyles and increased lateral chewing muscles extend along the front of the zygomatic arch. This method occurs in many types of rodents such as porcupines, guinea pigs, and jumping rats.

3. Like the squirrel-type model, the maxillary condyles are enlarged in a disc shape, changing the starting point of the front lateral chewing muscle. The hole under the frame is relatively large, and some middle chewing muscles pass through it.

How the three modes of masticatory muscles evolved has been highly debated by scholars. However, the three models of masticatory muscle evolution have been accepted by most scholars. At least the evolutionary results can be seen in many rodents.