Mammalia, a subclass of vertebrates, commonly known as mammals[4]。Mammals are senior vertebrates with hair, viviparity and lactation. They have highly developed nervous system and sensory organs and can coordinate complex functional activities.Body covered sweater, high and constant temperature, reducing dependence on the environment.Heteromorphic teeth and developed oral glands.Oral digestion occurs, improving the utilization rate of food.Fetal birth (except for a few), breastfeeding behavior improves the survival rate of offspring.[5]It is named for the milk secreted by the mammary gland to feed the baby.[4]
There are many mammals, which are distributed in every corner of the world except Antarctica, the central region of the Arctic and individual islands.Mammals can live in water, land, underground and air, with carnivores, herbivores and omnivores.Mammals have a strong adaptability to extremely harsh environments, and they have their presence in deserts, mountains, grasslands and arctic alpine regions.[4]Existing mammals can be divided into three groups.The first is monotreme, also called protozoa, which represents the platypus.These animals reproduce by eggs, which is the lowest level of evolution among mammals.The second kind is marsupial, also called post mammal, representing kangaroos.This kind of animal can not be separated from the mother body directly after birth, and must develop in the pouch for a period of time.The third is the placental species, which is the highest stage of mammalian evolution, also known as true mammals.Including all mammals except protozoa and metazoans, it is also the main body of modern mammals.[6]
Biologists found that the earliest mammals appeared 125 million years ago, when there were reptiles and dinosaurs living on the earth.[4]Mammals are very successful animals.They can occupy almost every terrestrial habitat[7]。Humans are also mammals, belonging to primates.[8]
Like birds, mammals evolved from reptiles.Mammals are senior vertebrates with hair, viviparity and lactation. They have highly developed nervous system and sensory organs and can coordinate complex functional activities.Body covered sweater, high and constant temperature, reducing dependence on the environment.Heteromorphic teeth and developed oral glands.Oral digestion occurs, improving the utilization rate of food.Fetal birth (except for a few), breastfeeding behavior improves the survival rate of offspring.It is named for the milk secreted by the mammary gland to feed the baby.Mammals have the highest evolutionary status in the animal kingdomNatural group。
Biologists found that the earliest mammals appeared 125 million years ago, when there were reptiles and dinosaurs living on the earth.Mammals are very successful animals.They can occupy almost every terrestrial habitat。Humans are also mammals, belonging to primates.[4-5][7-8]
Evolutionary history
The earliest mammals wereTheropodaIt evolved.Real mammals emerged at the end of the Triassic in the Mesozoic era. After entering the Cenozoic era, mammals replaced dinosaurs to occupy the niche advantage, and evolved into today's diverse mammalian populations.
history
According to the fossil evidence currently available to humans, mammals are believed to have first appeared in themesozoicOfthe triassic period, and onCenozoic eraIt began to flourish and has become the dominant animal on the land until now.The earliest mammalsFossilIt was found in ChinaHadrocodium wui (Hadrocodium wui), which lived 200 million years agojurassic period。From the perspective of fossils, the most important difference between mammals (especially early mammals) and reptiles is their teeth.Each tooth of reptiles is the same and does not differ from each other, while the teeth of mammals differentiate into different shapes according to their different positions on the jaw.In addition, the teeth of reptiles are constantly updated, and the teeth of mammals are no longer updated except for baby teeth.In the animal kingdom, only mammals have three bones in their ears.They evolved from two jaws of reptiles.
There is fossil evidence thatthe triassic periodIn the middle period, the skulls of some foraminifera began to produce many new features.In reptiles, the mandible composed of multiple bones evolved into a single tooth bone, and the teeth also evolved from a single shaped tooth to a variety of shapes according to the position in the mouth.Buccal arch becomes more developed to supportMasticatory muscleThe need for reinforcement.Their body bones become light and flexible, and their limbs are upright rather than stretching sideways like reptiles.They have well-developedcoat, so it may beThermostatic animal。It can be considered that they are in the process of transition to real mammals.
mesozoicAll mammals are very small.After the extinction of dinosaurs, mammals occupied many ecological niches.reachthe quaternary periodBy then, mammals had become the dominant animals on land.
In the late Triassic period, about 200 million years ago, early mammals and dinosaurs officially appeared almost at the same time.At that time, dinosaurs of all sizes that landed on the land accounted for most of theNicheThe size of early mammals was insignificant, and they mainly depended on insects and other small prey living in the jungle.By 65 million years agoCretaceousAt the end of the period, dinosaurs may quickly become extinct due to climate change, while mammals have constant temperature characteristics, and their small bodies reduce the loss of heat, helping them survive in low temperatures and dark nights.
Cenozoic era
stayPaleogeneBefore that, all mammals were very small, all of them were small hunters with a body length of about 12cm, similar to that of mice.After entering the Cenozoic era, dinosaurs declined, so mammals were able to occupy moreNicheAnd rapidly evolved into richDiversityOf thousands of different species.The earlybatandwhale；Until 40 million years ago, all orders under Mammalia basically appeared today.
here we arethe quaternary periodMammals have become dominant animals on land.althoughGlaciationLet includeMammothA number of large mammals were wiped out, but most of the species that have survived have not changed much.
The Ice Age led to the extinction of a number of large mammals and the emergence of modern humans.
morphological character
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Most of the body is covered with hair;temperatureconstant；Viviparity(Monotremes excepted) and lactation;heartThe left and right chambers are completely separated,Left ventricleThe blood is pumped to all parts of the body through the left arterial arch;Craniumexpand,Brain volumeIncrease;middle earWith 3Ossicle；The mandible is composed of one tooth bone, which is articulating with the skull in the form of tooth squamous bone;The teeth differentiate intoIncisor、Canine toothandBuccal tooth；7 cervical vertebrae, the first and second cervical vertebrae differentiate into the ring vertebrae andaxis。The advancement of mammals is shown in the following aspects: highly developed brain;Constant temperature and prenatal lactation.Mammalia has a complex body structure, which is different from other groupsBrain structure, thermostatic system andcirculatory system, have the ability to breastfeed for offspring, most of them belong toViviparityIt has the common external characteristics of hair follicle and sweat gland.They have various shapes, as small as 30mm long with wingsConcave faced bat, up to 33 meters long, similar to fishBlue whale。It has a highly developed nervous system and senses, can coordinate complex skill activities and adapt to changing environmental conditions, and is far superior to other groups in intelligence and response to the environment;
Mammals are in the animal kingdomdiversificationThe highest level.Their body structure should meet the needs of the living environmentSpecialization。Largest mammalBlue whaleWeight (150 tons) is almost the smallestConcave faced bat(2g).Their shapes are also strange.for examplegiraffeIt has evolved a neck that is 2 meters long and can protrude 45 centimeters from its mouthtongue；elephantHas a nose as flexible as a human hand;dolphinLooks like a fish;Like birds, bats have wings to fly in the air.
Mammals have hair, highly developed nervous system and sensory organs.The body temperature is high and constant, reducing dependence on the environment.Heteromorphic teeth and developed oral glands.[1][5]
Main Characteristics of Mammals
type
features
annotation
Soft tissue characteristics
warm-blooded animal
Mammals maintain a constant high body temperature by generating heat inside their bodies
Hair follicles and sweat glands
The smooth looking whale family actually has a small amount of hair on some parts of its body
There are ossicles in the ear, which are composed of three bones: malleus, incus and pedal bone
lower jaw
The lower jaw consists of a single piece of dental bone
Habitat environment
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Adapt to multiple environments
Mammal habitats can be water, land, underground and air.It can adapt to extremely harsh environments, such as deserts, mountains, grasslands and arctic alpine regions.
Mammals are the most widely distributed species in the animal kingdom.As a classThermostatic animalThey can maintain their activity ability in a cold environment, and sweat glands and other organs can help them control their body temperature in a hot environment, so they can adapt to living environments with different temperatures and terrains.fromSavannaOnantelopereachpolar regionOfPolar bearAnd then to the mountainsPikaCamels and camels in the desert can be seen everywhere.Although they mainly live on land, some species have adapted to live outside the land environment, such as flyingbatAnd living in the oceanSeals、dolphinEtc.[1][4]
Desert
camel
The main feature of the desert is drought. In addition, it is accompanied by severe day night temperature difference, sandstorms and other bad weather, and food is scarce.Mammals adapted to the desert environment have evolved a series of unique survival skills to manage energy and water, resist the hot climate and carry out regular migration.
Energy and Water Management
Desert mammals have different ways of obtaining, processing and losing water.Predators generally get water from their prey's blood and wet tissues,HerbivoresGenerally, they get water from the plants they eat, and sometimes they lick the water coagulated on the surface of rocks and plantsDew。In addition to the part obtained directly in the form of water, they can effectively use the metabolic water generated in the digestion process.In order to reduce water waste, they have efficient kidneysurineIt is highly concentrated and the feces are very dry.Some desert mammals, such as camels, will eat a lot when the water and grass are abundant, and store energy and water on the backhumpInternal;Fat tailed jerboas store excess energy at the base of their tails.Small mammals that eat seeds also store them in caves,Kangaroo rat 5 kg of seeds can be stored in caves.
Resistance to heat
In order to reduce excessive water loss due to sweating, many desert mammals will find cool places to rest in the daytime, such as the shadow of hills and bushes. Small mammals such asJerboaThey will hide in the cave and feed actively in the cool morning and dusk.At night, because it is difficult to find predators, large herbivores will move at night, moving from one feeding place to another, chewing ruminant food while walking.elandIt can move more than 30 kilometers at night.Some small mammals, such asAuricular foxLarge ears evolved to dissipate heat.The body temperature of many desert mammals can be raised a little higher than normal to reduce sweating.
Regular migration
Mammals living in the desert need to migrate regularly to ensure adequate supply of food and water. They have the ability to travel long distances no matter how big or small.Some large herbivorous mammals have a very sensitive sense of smell to water vapor, and can roughly know the location of rainfall and migrate to it, while carnivores will follow.Allactodipus bobrinskii It can move 10 kilometers in one night.
forest
Great lemur
The natural environment with the richest forest biodiversity.The forest land provides animals with rich food resources and hiding places to protect them from predators on the ground.The mammals living in it have also evolved the characteristics suitable for the species environment.
Arboreal and terrestrial life
Some forest mammals such asVillous monkey、Spider monkeyIt almost never goes down to the ground.And Diao andTigressOthers are semi arboreal.Arboreal mammals move from branch to branch by jumping, leaping, etc.Old WorldGibbonUsing hooked hands to grasp the branches, American monkeys use their powerful tails to wrap the branches.The tail of the spider monkey can support the weight of the whole body.Squirrels have sharp claws to grasp the bark and balance their bodies with their big tails.Flying squirrelsMarsupialThere are pellicles between the limbs, which can glide among trees.Bats have the ability to fly completely.mice、wild boar、Tapir, deer and other mammals walk on the ground of forest land.Small mammals such as squirrels often use tree holes to build nests. Wild boars and deer will use trees, hillsides and other terrain to find suitable resting places to avoid being attacked from all sides.Many arboreal mammals rest directly on the branches.
camouflage
Most of the fur of forest mammals is a mixture of different shades of brown, so it blends into the background of the living environment.The young deer and wild boar have striped fur, which is easy to mix with the color at the bottom of the forest land.The speckled texture on the arboreal cats is easy to mix with the light transmission and mottled shadows among the branches on the trees.
Grassland
Wildebeest
The grassland is an open environment. Occasionally, there are scattered trees and shrubs. The climate is basically dry throughout the year, but there are also large-scale seasonal storms.These characteristics have led to the evolution of grassland mammals into an integrated community and regular migration by season.In order to avoid natural enemies, they either evolved the ability to move at a high speed or dug holes to live in caves.
Aggregate community
Large herbivorous mammals converge into large communities to reduce the risk of becoming a single target. Some individuals often have other individuals on alert when eating and resting.Sometimes different species will mix together.In AfricaSavannaOn,zebra、antelope、Gazelle、giraffeIt is the largest wildlife community in the world. Giraffes have a large field of vision and visual distance in open areas, while zebras are sensitive to smell and antelopes are sensitive to hearing. They share superior resources and reduce the risk of predation.
Regular migration
Rainfall in the tropical grassland is local and seasonal.Large herbivorous mammals live by water.WildebeestIt is famous for large-scale and regular migration.
High speed movement ability
The open area of the grassland is short of cover, so it is not easy to ambush or escape.Carnivores have evolved the ability of rapid movement in order to capture herbivores and survive herbivores.AfricanCheetahRunning speed can exceed 100 kilometers per hour, and their preyPronghornTheir speed is no inferior. They are the fastest running mammals.In addition to speed, some other mammals such aswild horseThey have evolved the ability to run continuously and quickly, allowing them to travel long distances on the boundless prairie.
Cave dwelling
Some small mammals such asPrairie dog、moleI will dig holes in the grassland to build a hiding place.They will build complex and highly organized tunnel systems underground.Some tunnels will be built with waterproof mounds and drainage facilities.AfricanAardvarkThe hole can even accommodate one person.In addition to avoiding natural enemies, tunnels can also provide shelter when prairie fires strike.
Polar mountain
Yak
The climate in the polar regions and high altitude areas is cold, some are covered with ice and snow all year round, and food is scarce.Under such harsh conditions, mammals have evolved various strategies to deal with them.
keep warm
Mammals living in cold environments all have multiple hairs, and the outer long hairs mainly protect the body, camouflage, and prevent water and snow.YakThe hair can be up to 1 meter long.The base layer of hair is a thick layer of hair, which has a warm effect.Many mammals have a thick layer of hair on their feet, such asPolar bearAnd wolves, in addition to keeping warm, can also slip on the surface of ice and snow.Polar bears andSealsThere are thicksubcutaneous fat Wrap to reduce heat loss.Their protruding organs, such as nose and ears, become shorter to reduce the risk of frostbite caused by rapid cooling of these parts.Arctic foxThe thick and short body evolved from small mammals, such as mammals, reduces the body surface area relative to their body size, and reduces the loss of body temperature as much as possible.
Seasonal molting
In polar and alpine environments, because of the relationship between snowfall and snow melting, the environmental color changes greatly in different seasons.In order to effectively camouflage in different seasons, many polar mammals, such as the arctic fox andArctic rabbitThey change their hair twice a year. In summer, they change to brown and dark brown fur, which is similar to the color of rocks, soil and shrubs. In winter, they change to snow-white thick fur, which blends into the white background.
alpine environment
The air at high altitude is thin. In order to improve the body's ability to transport oxygen, many alpine mammals have higher density of red blood cells in their blood.The hoofed mammals living in the mountains have well-developed limbs, such asBlue sheepSuch species have evolved a sharp and hard outer edge and a soft cushion inside, which can maintain good grip on slippery and steep rock walls.They live on nearly vertical cliffs to avoid predators.
aquatic
dolphin
The body design of mammals living in water is very different from that of mammals on land.
Suitable for swimming
Water is denser than air and has greater resistance.In order to move quickly in the water, aquatic mammals have evolved smooth and streamlined bodies.Completely aquaticdolphin、whale、dugong、ManateeThe tail fin and trunk move in waves to promote the degeneration and disappearance of the hind limbs, while the forelimbs evolve into fin like limbs to control the direction,DolphinidaeMost mammals ofDorsal fin, which can prevent rolling during traveling.Semi aquatic mammals such asOtter、SealsIn order to meet the needs of life on land, they still have thick hair, and their limbs have also evolved into paddle shaped or fin shaped limbs.Sea lionsThe forelimbs are mainly used to push the body, while seals mainly use the hind limbs.Aquatic mammals are more capable of locomotion in water than many fishgo beyond。
heat preservation
Many aquatic mammals live in the polar regions or migrate to the polar regions seasonally.In order to maintain body temperature in cold sea water, they have evolved larger body size and smaller protruding organs on the body surface, so as to reduce the ratio of body surface area to body volume, thereby reducing heat loss.They also have thick subcutaneous fat to keep out the cold.Some species that want to live ashore, such as seals, sea lions and otters, have very thick fur, and the hair surface is also covered with waterproof grease.They reduce the energy consumption of the body to generate heat by basking in the sun on the shore.
breathing
Mammals breathe with their lungs. They must return to the sea regularly to breathe fresh air.The myoglobin in animal muscle can preserve oxygen and slow release, while the myoglobin content of aquatic mammals is high, and the myoglobin content of some kinds of seals can be more than ten times that of terrestrial mammals.[2]
Life habits
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Population characteristics
Highly developed nervous system and senses can coordinate complex functional activities and adapt to changing environmental conditions.
Constant temperature (about 25-37 ℃), perfectThe blood circulatory system, body surface hair coat with excellent heat insulation performance and othersThermoregulationIt provides a stable internal environment and reduces dependence on the external environment, which is different from cold-blooded animals;
Fetal lactation, except the most primitiveMonotremeOogenesisOutside, allViviparity。Advanced species form the tissue (placenta) between the embryo and the uterine wall for the exchange of maternal and fetal nutrients.The mother animal suckles and nurtures her cubs for a long time, so that their offspring have a higher survival rate. The cubs can also acquire adaptive skills through learning;
Presence of oral cavitychewAnd digestion, greatly improving the energyIngestion；
Have the ability to move quickly on land.It includes carnivores, herbivores and omnivores.The living habits of mammals vary from species to species, such as migration and hunting behavior.[4]
Life adaptation
motion
The five toed limbs of primitive mammals that are suitable for walking on the ground derive many specialized types with different lifestyles, such as those for aquatic lifewhaleClass andManateeThe hind limbs of class A degenerated, and the forelimbs evolved into fins;Adapted to flying lifePteropteraOfPhalangeLengthened, developed between fingers and limbsPterygoid membrane；Living undergroundmoleThe forelimbs of the class are shovel shaped and run in the open grasslandUngulatesIn order to reduce the weight of the limbs, huge muscles are located in the buttocks;Arboreal beasts or animals with sharp claws are easy to climb on tree trunks, such assquirrelClass, or with long fingers (toes) for grasping branches, such asprimatesThere are also very special mammals adapted to arboreal movement, such as those in tropical forests of South AmericaslothIts toe end has huge hook like claws for climbing and hanging on trees.
Feeding habits
Primitive beasts are mainly omnivores that feed on insects.Later, it evolved into:omnivore , withAnimals and plantsFor food;Herbivores feed on plants;Carnivores feed on animals.
Each category can be subdivided into many types.Many changes have taken place in the teeth and masseter muscles of herbivores,RodentandLagomorpha It has developed chisel shaped incisors that can grow for a lifetime to adapt to biting rough and hard barknutEtc;BovidaeandDeer FamilyThe upper teeth of animals disappeared, and thick skin pads were used instead to adapt to breaking grass stems.Canine teeth often disappear in herbivores, while buccal teeth expand into an effective grinding structure.Carnivores, on the contrary to herbivores, have well-developed canine teeth, which are easy to pierce the catch.The number of molars tends to decrease, and the split teeth composed of the fourth upper premolar and the first lower molar are suitable for tearing.The most special ones are variousAnteater, such asPangolin、Anteater、Aardvark、Echidna、Bag anteaterAs a result of the convergence of their lifestyles, their teeth are extremely degraded, and they have developed a long and mucus rich tongue suitable for licking ants.
Environmental adaptation
When the environmental conditions tend to be extreme, the adaptation of mammals is very obvious.For example, inDesertEnvironment, camel andJerboaThere are many adaptations to keep water: reducing water in urine, not using water to regulate body temperature (sweating), making full use of water generated by decomposing food, living in caves, walking at night, etc.Polar environmentalArctic foxThey all have very warm fur.
Distribution range
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Mammals are widely distributed in all parts of the world, except Antarctica, the central region of the Arctic and individual islands.[4]
In monotremeEchidnaandplatypus, produced in AustraliaTasmaniaandNew GuineaThere are only 1 order, 2 families, 3 genera and 3 species.
In addition to Protozoa and Euzoa, Mammalia also includes metazoa, including variousMarsupial, produced in the southNorth America、AustraliaAnd its adjacent islands, totaling 7 orders, 19 families, 86 genera and about 250 species;Euzoa, including variousPlacenta, spread all over the world.
Each region has its own unique mammal fauna, including unique orders, families, genera, species and subspecies.The difference of mammal fauna between the world's animal geographical communities is growing from north to south.stayPalaearcticandNew Northern TerritoryThere are many common species, only subspecies differences, in the north of;There began to be different species and genera in the south;Further to the south, there are different families and orders in different regions.China straddles the Palaearctic and Oriental borders, and the north belongs to the Palaearctic.
Specific distribution
Mammals are widely distributed all over the world. They live on land, underground, aquatic and fly in the air;There are three types of nutrition: herbivore, meat and omnivore.
Monopore：The most primitive mammals in existence, includingplatypus、Echidna, long billed echidna, oviparous, only distributed in Oceania and New Guinea.
Metazoa：That is, there are bags with only one eye, but some people also divide them into different eyes.
Eucerata：That is to say, there are placentas, the dominant mammals of the Cenozoic era, and only mammals of this class in China.
Insectivora：The most primitive members of Euzoa, which are very similar to the common ancestors of other Euzoa, are now distributed in Oceania, southern South America and most areas outside Antarctica, with a wide range of species.Now divided intoErinaceomorpha 、African hedgehogandSoricomorpha 。
Dermatoptera：Small order of tropical Asia, including only two speciesLemur。
Chiroptera：I.ebat, flying mammals, the second largest order of mammals, all over the world outside Antarctica.
Primates：They include apes, lemurs, and humans. Except for humans, they are mostly distributed in warm areas outside Oceania.Generally, according to the degree of evolution, it can be divided into primitiveProtomonkeysModerately progressive monkeys and progressive apes and humans.
Anodonta：Primitive taxa now only distributed in America, includingarmadillo、Anteaterandsloth。Now, taxonomy has abolished the order Anadenta and upgraded the original order Anadenta toTenebriata, the suborders Epitrichales and Vermiculoglossia are merged intoPilosa 。
Lagomorpha：Including rabbits andPika, distributed all over the world outside Oceania and Antarctica, and introduced into Oceania.
Rodentia：The largest order of mammals, which covers all parts of the world outside Antarctica, namely all kinds of mice, porcupines, beavers, etc., are generally divided intoSquirrels、MurineandPorcupinesThree categories.
Carnivora：Including terrestrial schizopods and marine onesPinnipedsThey are often divided into different orders and widely distributed all over the world. Schizopods are also divided into dog type and cat typeMustelidaeAnd felineFelidaeIntroduced separately.
Hymenoptera：VegetarianMarine mammalsIt is now distributed in tropical and subtropical coastal areas of all continents, as well as some freshwater waters in Africa and South America.
Finopoda: distinguished from ancient carnivoresCarnivoraAnimals are close relatives.A large water handle carnivore that grows into the water. It is aquatic.It is distributed in the cold and temperate oceans of the southern and northern hemispheres.Now the classification has reduced the pteropoda to the suborder of pteropodaCarnivora。
dolphin
PyrolaA small order now distributed only in Africa and Arabia.
Long Nose：Elephants are now only distributed in tropical Africa and Asia.
Odaria: ungulates in decline, including horsesTapirandrhinocerosThree types are distributed in Africa, Asia and Central and South America.
Whale Artiodactyla：Modern advantagesUngulates, distributed all over the world outside Oceania and Antarctica, including the suborder of swine,CallopodaandRuminantsAmong them, the bovine family of ruminants is the most advanced and prosperous ungulates.includewhaleanddolphin, widely distributed in the world's oceans, some of which are the largest animals on the earth.
Reproductive mode
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Mammals reproduce through viviparity and feed their young by secreting milk from their mammary glands.
Fetal lactation, except the most primitiveMonotremeOogenesisOutside, allViviparity。Advanced species form the tissue (placenta) between the embryo and the uterine wall for the exchange of maternal and fetal nutrients.The mother animal suckles and nurtures her cubs for a long time, so that their offspring have a higher survival rate. The cubs can also acquire adaptive skills through learning;
Late Mesozoiccrustal movementWhen the environment changes significantly, dinosaurs and other reptiles are difficult to adapt and survive, while mammals show strong competitiveness;Mammals have a good ability to adapt to the environment. They have constant body temperature and mammary glands. They can breastfeed their young. Their brains are developed, and they can control their actions. They are born at birth (except for monotremes), which is conducive to the continuation of their offspring.All these have provided their own advantages for their growth and development.After entering the Cenozoic era, placental mammals have become a large familymain streamThe vast majority of fossils and living mammals belong to the placental class.There are about 30 orders of placental mammals, and carnivores (such ascatamount)、Rodentia(such as various rodents), Artiodactyla (such as pigs, cattle, sheep, etc.), Chondrea (such as horses, donkeys, etc.)Primates(e.g. monkey andapeClass), Chiroptera (such asbatEtc.), long nose (such as elephant) and cetacean (such asdolphinEtc.).[1][4-5]
Mammals are divided into monotremes, marsupials and placentas.Monopore: represented by platypus.Baggy category: represented by kangaroos.Placenta: including all mammals except protozoa and metazoans, it is the main body of modern mammals.There are 4237 species belonging to 1042 genera, 123 families, 19 orders.
Mammals (including fossil and living species) can be divided intoProtozoa、MetazoaandEucerata。Protozoa includes extinctMesozoic mammalsAnd nowMonopore。According to the data of Mammal Species of the World in 2005, there are about 5676 mammals (2008 editionIUCN Red Book5488), distributed in 1229 genera, 153 families and 20 orders, accounting for aboutChordate10%, 0.4% of all species on the earth.Rodentia（mouse、porcupine、beaver、capybara) is the order with the most species in mammals,Chiroptera（batEtc.),Insectivora（Shrew、mole, hedgehog, etc.)Artiodactyla(Antelopes, buffaloes, pigs, deer, etc.) and carnivores (lions, tigers, foxes, leopards, cats, etc.).[6]
Research data shows that there are at least 351 mammal species in the past 126000 yearsExtinction80 of them are known from historical data after 1500 AD, and the others are only determined by fossils.This shows that the extinction rate of animals has been increasing over the years, and the observation results of birds, reptiles, amphibians and ray fin fish also prove this.
In order to assess the severity of the threat posed by current trends to biodiversity, experts from the University of Gothenburg, Sweden, collected data on mammal extinction over the past 126000 years.They analyzed the changes in the rate of extinction, determined the specific period when the rate of extinction accelerated, and compared it with the changes in the number of human beings in the same period.The results were published in the journal Progress of Science.
Experts found that the current extinction rate is about 1700 times that of the early Late Pleistocene.Based on the current level, 351 species of animals would only need 810 years to become extinct, but if the rate of 126000 years ago was maintained, 351 species of animals would need about 1.75 million years to become extinct.In addition, research shows that the extinction rate has accelerated significantly in four periods, namely 63800 to 32200 years ago, 16000 to 9500 years ago, 2300-600 years ago, and 180-120 years ago.
The computer model data shows that the first two periods partially coincide with the time of colonizing Australia (65000-44000 years ago) and the Americas (24000-12000 years ago).Experts therefore judge that human activities are the main reason for the extinction of animals.They studied the impact of population size and human activity area on the speed of animal extinction.The results show that the accuracy rate of population density reflecting the extinction rate is about 97%.Experts believe that this data is also related to other human factors, including the development of hunting and agriculture, fire use, deforestation and urbanization.
Experts said that compared with the prediction of animal extinction in the next 80 years, the current research results are insignificant.They believe that by 2100, the threat to biodiversity will increase seriously, with 502 to 610 species of mammals going extinct.Africa, the Americas and Eurasia are likely to have a large number of animal extinctions: the rate of animal extinctions in all continents remains at a low level, but there are many endangered animal species.Strong environmental policies can help reduce the threat of extinction.[3]
