What animal does a dog belong to?

Introduction of dogs:

Dogs belong to Chordata, Vertebrate, Mammalia, Orthoptera, Carnivora, Schipoda and Canidae. Dog, also called "dog" in Chinese, belongs to Carnivora and is distributed all over the world. Dogs, horses, cows, sheep, pigs and chickens are also called "six animals".

Some scientists believe that dogs were domesticated by early humans from gray wolves. The domestication time was from 40,000 years ago to 1.5 million years ago, and it has developed to this day. Known as "the most loyal friend of mankind", it is the pet with the highest feeding rate at present. Its life span is about ten years.

In China culture, dogs belong to one of the 12 Zodiacs, ranking 1 1 among the 12 Zodiacs.

Expand knowledge about dogs;

The ancestors of dogs:

No one knows exactly when the first interaction between man and wolf took place. Some scientists think it may be 50,000 years ago, because it took wild wolves at least so long to show today's genetic differences. At that time, humans and wolves were distributed in many places on the earth's surface, and the evolution process may have occurred in several different areas. Some scholars believe that wolves were domesticated from wild wolves to domestic animals for playing, hunting and housekeeping, that is, dogs, before 14000 years or even before 16000 years in Southeast Asia.

Dogs originated from wolves and have been recognized, but opinions vary around the specific place of birth and time. The earliest evidence of dog fossils comes from a mandible fossil in Germany 14000 years ago. These archaeological evidences support that dogs originated in southwest Asia or Europe. On the other hand, the characteristics of dog skeleton identification suggest that dogs may have originated from wolves, thus putting forward the origin theory of East Asian dogs. In addition, different breeds of dogs are very diverse in morphology, which seems to be inclined to the hypothesis that dogs originated from wolves of different geographical groups. Archaeology alone can hardly provide reliable clues about the origin of dogs.

Life span of dogs:

(1) The age of a dog is mainly judged by the following points:

① Tooth growth (see "Dogs-Physiology-Teeth" for details);

② the degree of tooth peak and tooth wear;

③ Appearance color.

(2) In general, the life span of dogs is between 10 ~ 15 years, with an average life span of about 12.6 years and the longest life span of about 20 years.

Characteristics of dogs:

(1) dog's sense of smell:

Dogs' olfactory sensitivity ranks first among all animals, and blind dogs can live like normal dogs with their noses. Dogs' acute sense of smell is mainly manifested in two aspects: first, they are sensitive to smells; The second is the ability to distinguish smells. The sensitivity will vary according to the kind of taste, which is about 1200 times that of human sense of smell. The dog's nose can distinguish about 2 million different smells, and it also has high analytical ability, and it can sniff out the smell it is looking for from many mixed smells. Dogs can perceive smells at the molecular level. For example, when 1 cubic centimeter contains 9000 butyric acid molecules, dogs can smell it, while in general, there are about 268× 10.e+ 16 molecules in the air per cubic centimeter. So the concentration of butyric acid felt by dogs is 3.36× 10.e- 17. When someone dilutes sulfuric acid by one millionth, dogs can still smell it, and their olfactory sensitivity to acidic substances is tens of thousands of times higher than that of people.

According to the European Lung Disease Foundation, lung cancer is the second leading cause of death in Europe. It was found that dogs trained in olfaction could sniff out 7 1 case from the breath samples of 100 patients with lung cancer, and the discrimination accuracy of non-lung cancer samples could reach 372/400.

(2) the dog's hearing:

The auditory induction can reach1.2000 Hz, which is 6 times that of human beings. The farthest listening distance is about 400 times that of human beings. Dogs are also twice as able to distinguish the direction of sound as humans, and can distinguish 32 directions. It can be distinguished that the number of times the metronome vibrates per minute is 96 or 100, 133 or 144. For human passwords and simple languages, dogs can establish conditioned reflex according to the changes of tone and syllable.

Dogs can hear 40,000 cycles. The sound collected through the big ears vibrates the eardrum through the external auditory canal, even vibrates the ossicles of the middle ear, reaches the lymph of the inner ear, and then reaches the brain through the auditory nerve. Dogs can distinguish tiny or high-frequency sounds (ultrasonic waves). The ability to judge the sound source is also very strong. When a dog hears a sound, it can see and hear all directions with its eyes because of the sympathetic action of its ears and eyes. At night, even if you sleep, you should be highly alert and can clearly distinguish the sounds within the range of 1 km. In particular, we don't need to yell at the dog. Too much sound or audio is a kind of adversity stimulus for it, which will make it feel pain, fear or panic.

(3) the dog's eyesight:

Dogs' eyesight is only about three-quarters of that of humans, and among all animal species, dogs' eyesight is about medium. The dog can only see 25 degrees with one eye, so it can't see the nearest distance ahead. The lens of a dog's eyeball is relatively large and deformed like a horse's eyeball, so it is impossible to adjust the sense of distance. Twenty or thirty meters is probably its limit. Dogs have a special ability to detect moving objects; They can detect images that move 70 lines per second, while ordinary TV images move 60 lines per second. Dogs have better eyesight than people in dim light. Dogs are natural carnivores and live by hunting, so they also have considerable vision in the dark. Dogs' eyes can see short-wavelength colors. In addition, the dog's cornea is bigger, which allows more light to enter the eyes, so it is easier to see things in dim light. But in the darkness without light, dogs can't see.

The difference between human vision and dog vision lies in the reaction to light. The human eye reacts to the three primary colors (red, green and blue) that cause various colors. Dr DennisBrooks, associate professor of ophthalmology at the College of Veterinary Medicine, University of Florida, said that dog vision is different from human vision. Dogs can't tell colors like people, but they can see some colors. Dogs can distinguish different shades of blue, indigo and purple, but they are not particularly sensitive to high chroma colors such as red and green in the spectrum. Dr. Brooks' research shows that red is dark for dogs and green is white for dogs, so the green lawn is white for dogs.

(4) the dog's teeth:

Dogs have short crowns. The crowns of the first and second maxillary incisors are three-pointed, with canine teeth in the middle and small peaks on both sides. The other front teeth have two small peaks, and the canine teeth are conical and extremely sharp, which is a powerful weapon for attack and self-defense. The front teeth are three-pointed, and the Japanese teeth are multi-pointed.

① Adult canine teeth (permanent teeth) consist of 42 incisors, canine teeth, premolars and molars.

② Teeth types of puppies: 28 incisors, canine teeth and premolars, with premolars and molars missing 1 tooth.

(5) Sweat glands of dogs:

Canine animals, such as dogs and wolves, have underdeveloped sweat glands. Unlike people, they can't regulate their body temperature by sweating. Once their bodies get hot, it is difficult to lower their body temperature, so dogs are very afraid of heat.

Dogs also have exocrine sweat glands and apocrine sweat glands. Exocrine sweat glands used to regulate body temperature are only distributed on the meat pads of four claws, and there are few. It is impossible to lower the body temperature just by sweating on the paws. The apocrine glands that cause their body odor are distributed all over the body and have nothing to do with body temperature regulation.

As long as the dog feels a little hot, it will open its mouth and stick out its tongue to gasp, and it can secrete a lot of saliva instead of sweat. Dogs evaporate saliva to give off heat and lower their body temperature. They drool a lot and absorb heat through saliva evaporation to lower their body temperature. When the weather is hot, it is impossible to cool down smoothly by this method alone. So it is difficult for dogs to lower their body temperature. Especially pug, bulldog, poodle, chihuahua and other small dogs, because of their short respiratory organs, are not good at regulating body temperature, especially afraid of heat, so we should pay more attention.

(6) Dog's intestines and stomach:

The digestive tract of dogs is shorter than that of herbivores, and the hydrochloric acid content in dogs' stomachs ranks first among domestic animals. In addition, the intestinal wall is thick, the absorption capacity is strong, and it is easy to digest meat food.