The process of mammalian evolution, what the early mammals gradually evolved

Mammals.

Like birds, mammals evolved from reptiles. Mammal.

It is a class of the subphylum Vertebrates, commonly known as mammals. Most mammals are vertebrates with hair, fast movement, constant temperature viviparity, and diaphragm in the body, and are the most complex group of vertebrates in terms of body structure and functional behavior. Mammals can be divided into protozoan subclasses, euzozon subclasses, and posterior zonal subclasses.

Mammals are found all over the world and live a variety of lifestyles on land, underground, in the water and in the air. There are three types of nutrition: herbivorous, carnivorous, and omnivorous.

2. The earliest mammalian fossil is the Wu mega-cranial beast found in China, which lived in the Jurassic period 200 million years ago.

Fossilly, a very important difference between mammals (especially early mammals) and reptiles is their teeth. Each tooth of a reptile is the same and does not differ from each other, whereas the teeth of mammals differentiate into different morphologies according to their different positions on the jaw. In the animal kingdom, only mammals have three bones in their ears.

All mammals in the Mesozoic era were small. After the extinction of the dinosaurs, mammals occupied many ecological niches. By the Quaternary period, mammals had become the dominant animals on land.

3. Mammalian evolution is through movement and the food chain.

The change is done. The five-toed limbs of primitive mammals, which are suitable for walking on the ground, have evolved into many specialized types as they adapt to different lifestyles, such as the vestigial hindlimbs of cetaceans and manatees, and the evolution of their forelimbs into fins; The phalanges of the winged hands adapted to flying life are elongated, and the wing membranes develop between the fingers and the limbs; Mole.

The forelimbs of the class are shovel-shaped, and the limbs of the ungulate running in the open grassland have hooves at the ends of the toes, and in order to reduce the weight of the limbs, huge muscles are located on the hips; Arboreal mammals have sharp claws for climbing on tree trunks, such as squirrels, or long fingers (toes) for grasping branches, such as primates.

There are also very specific mammals adapted to arboreal movements, such as sloths in the tropical forests of South America.

It has large hook-like claws at the ends of its toes, which it uses to climb and hang from trees. Primitive mammals were mainly omnivores that fed on insects. Later, due to adaptation to different lifestyles, they evolved into: omnivores, feeding on animals and plants; Herbivores feed on plants; Carnivores feed on animals.

IV. The evolution of sub-orders and masseter muscles in mammals. Each class of mammals can be subdivided into many types. Many changes have occurred in the teeth and masseter muscles of herbivores, and rodents and rabbitoids have developed chisel-shaped incisors that grow throughout their lives to adapt to gnawing on coarse bark, nuts, etc.; Bovidae and cervidae.

The animal's upper incisors disappear and are replaced by thick ** pads to accommodate tearing off grass stems. The canine teeth often disappear in herbivores, while the cheek teeth enlarge into effective grinding structures. Carnivorous beasts, in contrast to herbivorous beasts, have well-developed canine teeth that facilitate piercing of prey.

Molar number tends to decrease, consisting of the 4th upper premolar and the 1st lower molar.

At the end of the Carboniferous period, a group of mammal-like reptiles developed in the reptile trunk cuposaurus, that is, the Coilosaurus, which evolved into the Oriodonda, and a branch of the Orrodontosaurus evolved into the ancestor of mammals. The earliest mammals appeared around the end of the Triassic to the beginning of the Jurassic. In biological evolution, the origin of mammals is still relatively less controversial.

Early mammals gradually evolved the placenta because of the use of some of the virus's genes, and its most prominent feature is that viviparity and its young are fed by the mother's milk and have a relatively developed brain, so they can produce more complex behaviors than other animals.

Mammals are the most morphologically structured and physiologically functional animals in the animal world, and they all have fur to keep their body temperature constant. There are more than 4,000 species of mammals in the world, and although they are all highly evolved, they still have a lot in common, and almost all mammals are warm-blooded.

Although the nests of mammals are not as delicate as those of birds, they are varied and varied, and some marine animals, such as fur seals and seals, generally do not inhabit the water, but build their nests on the shore.

Early mammalian evolution

No one knows what the earliest mammals were like. But scientists have found fossils of a weasel-like paleontocrat in the Wales and Bristol regions of England, and the burrowing animal known as the Morgan-tooth is likely an early mammalian species.

These early mammals are said to be smaller, insect-feeding, nocturnal, hairy, and warm-blooded. In fact, this feature of warm blood is the first characteristic of the Ichroporeidae reptiles, who are probably the ancestors of mammals, and have witnessed the rise and fall of the entire Jurassic period along with the vast majority of dinosaurs, and even almost entered the Cretaceous period.

These early mammals were very close to the monotremes of the time and probably maintained an oviparous habit. Marsupial mammals and placental mammals as we know them evolved about 70 million years later.

Throughout the Jurassic period, mammals were short in size and mostly still preferred to be nocturnal, reminiscent of them walking under the feet of giant dinosaurs.

The earliest mammals evolved from the order Ichiodome in reptiles. True mammals emerged at the end of the Triassic period of the Mesozoic Era, and after entering the Cenozoic Era, mammals replaced dinosaurs to occupy the niche advantage, evolving into today's diverse mammalian populations.

According to the fossil evidence currently available to humans, mammals are believed to have first appeared in the Triassic period of the Mesozoic Era, more than 200 million years ago, and began to flourish in the Cenozoic, becoming the dominant animals on land to this day.

All mammals before the Paleogene were small, a small predator about 12 centimeters in length, similar to the size of a mouse. As the Cenozoic Era began, dinosaurs declined, allowing mammals to occupy more ecological niches and rapidly evolve into thousands of different species with rich diversity. Early bats and whales appeared 50 million years ago; By 40 million years ago, almost all the orders under the mammals had appeared.

By the Quaternary period, mammals had become the dominant animals on land. Although the Ice Age wiped out a number of large mammals, including mammoths, most of the species that survive to this day have not changed much.

Since the beginning of the Permian, reptiles have evolved into some mammals, such as hydrosaurons, dilodonts, and sharp tooths.

Mammals, like birds, evolved from reptiles. The earliest mammalian fossil is the Wu giant head found in China. Every tooth of a reptile is the same, while the teeth of a mammal differentiate into different morphologies according to their different positions on the jaw.

In the animal kingdom, only mammals have three bones in their ears. They evolved from the two jaws of reptiles.

Since the Permian (the last epoch of the Paleozoic Era), reptiles evolved into some mammal-like characteristics, that is, with common characteristics of mammals and reptiles, and some evolved into viviparous and lactation-secreting characteristics, and evolved into homeothermic animals, which later evolved into true mammals. Such as water dragons, two-toothed beasts, sharp-toothed beasts, etc.

Reptiles mainly include lizards, turtles, crocodiles, and snakes First of all, they crawl with their bellies close to the ground or nearly close to the ground, while mammals have their bellies much farther off the ground. So reptiles are more like crawling, mammals are more like walking. Second, reptiles lay eggs, and embryos develop in a hard shell (called oviparity), while mammalian embryos develop in the mother's body (called viviparity).

Third, the mother of reptiles cannot produce milk and nurse their young. Mammals, on the other hand, can (this is lactation). Viviparous mammals are the biggest feature that distinguishes mammals from reptiles.

Fourth, the body temperature of reptiles will change with the change of air temperature, so they are called ectotherms, also known as cold-blooded animals, while mammals have a constant body temperature and are homeotherms. Fifth, reptiles have scales, nails, and horns on the body surface, that is, they have no coat, while mammals are just hairy. Sixth, the reptilian heart is not a complete atria and ventricles, so his blood circulation is not as perfect as that of a mammal.

There are many more, I won't be verbose, if you are interested in going to university, you can take the biology major.

Primitive reptiles.

A mammal is a homeothermic, vertebrate animal with hair, mostly viviparous, and feeds its offspring through the mammary glands. Mammals are the most advanced stage in the history of animal development, and they are also the most closely related to humans.

The largest mammal: the blue whale.

The largest land mammal: the African elephant.

Tallest mammal: giraffe.

The fastest mammal: the cheetah.

The most smelly mammal: the American skunk.

What animals did primitive mammals evolve from?

a primitive fishes b primitive amphibians c primitive reptiles d primitive birds.

Take the platypus as an example, the monopore mammal in Australia, the most peculiar is the platypus. The so-called monotremes refer to an animal that is between reptiles and mammals. Although it is more advanced than reptiles, it has not yet evolved into a mammal.

The similarity between the two is that they both breathe with their lungs, have hair on their bodies, and are hot-blooded; Monopore, on the other hand, reproduce by laying eggs, thus retaining important characteristics of reptiles. Although it is listed as a mammal, it does not have the complete characteristics of mammals. It is the most primitive and lowest mammal, and is called "protozoars" or monopore oviparous mammals in animal taxonomy.

A group of ancient reptiles, the therodonts, gradually evolved into mammals.