Skeleton of animals: general characteristics and photos

Skeletons of different animals differ from each other. Their structure largely depends on the habitat and lifestyle of a particular organism. What is common in the skeleton of animals? What differences exist? What is the difference between the human skeleton and that of other mammals?

Skeleton - the support of the body

A firm and elastic structure of bones, cartilage and ligaments in the body of humans and animals is called the skeleton. Together with muscles and tendons, it forms a locomotor system, thanks to which living things can move in space.

Mostly it includes bones and cartilage. In the most mobile part they are connected by joints and tendons, forming a single whole. The solid "skeleton" of the body does not always consist of bone and cartilaginous tissue, sometimes it forms chitin, keratin or even limestone.

The amazing part of the body is the bones. They are very strong and tough, able to withstand enormous loads, but they remain light. In a young organism, the bones are elastic, and in time become more brittle and brittle.

The skeleton of animals is a kind of "pantry" of minerals. If the body suffers from a deficiency, the balance of the desired elements is replenished from the bones. Bones consist of water, fat, organic substances (polysaccharides, collagen), as well as salts of calcium, sodium, phosphorus, magnesium. The exact chemical composition depends on the nutrition of a particular organism.

Skeleton Value

The body of people and animals is a shell inside which there are internal organs. The shape of this shell is attached to the skeleton. Muscles and tendons are attached directly to it, cutting, they bend the joints, moving. So, we can lift a leg, turn a head, sit down or hold something by hand.

In addition, the skeleton of animals and humans serves as a protection for soft tissues and organs. For example, the ribs hide underneath the lungs and the heart, closing them from blows (of course, if the blows are not too powerful). The skull prevents damage from a fairly fragile brain.

Some bones contain one of the most important organs - the bone marrow. In humans, it participates in the processes of hematopoiesis, forming red blood cells. It also forms leukocytes - white blood cells, which are responsible for the body's immunity.

How and when did the skeleton originate?

The skeleton of animals and the whole musculoskeletal system arose from evolution. According to the generally accepted version, the first organisms that appeared on Earth did not have such complex adaptations. For a long time on our planet there were amoebae soft creatures.

Then in the atmosphere and the hydrosphere of the planet there were tens of times less oxygen. At some point, the share of gas began to increase, triggering, as scientists assume, a chain reaction of change. Thus, in the mineral composition of the ocean, the amount of calcites and aragonites increased. They, in turn, accumulated in living organisms, forming solid or elastic structures.

The earliest organisms that possessed the skeleton were found in the strata of limestone in Namibia, Siberia, Spain and other regions. They inhabited the world's ocean about 560 million years ago. In their structure, organisms resembled sponges with a cylindrical body. Radially from them departed long rays (up to 40 cm) from calcium carbonate, which acted as a skeleton.

Species of skeletons

In the animal world, three types of skeleton are distinguished: external, internal and liquid. The outer or exoskeleton is not hidden under the cover of the skin or other tissues, but completely or partially covers the animal's body from the outside. Which animals have an external skeleton? It has arachnids, insects, crustaceans, and also some vertebrates.

Like armor, it performs mostly protective function, and sometimes it can serve as a shelter for a living organism (shell of turtles or snails). Such a skeleton has a significant drawback. He does not grow with his master, causing the animal to periodically dump it and grow a new cover. At some period the body loses its habitual protection and becomes vulnerable.

The endoskeleton is the inner skeleton of animals. It is covered with meat and skin. It has a more complex construction, performs many functions and grows simultaneously with the whole organism. Endoskeleton is divided into the axial part (spine, skull, thorax) and additional or peripheral (limbs and bone belts).

The liquid, or hydrostatic skeleton is the least common. They have jellyfish, worms, anemones, etc. It is a muscular wall filled with liquid. The pressure of the liquid maintains the shape of the body. When the muscles contract, the pressure changes, which causes the body to move.

Which animals do not have a skeleton?

In the usual sense, the skeleton is the inner skeleton of the body, the totality of bones and cartilages that form the skull, limbs, and the spine. However, there are a number of organisms that do not have these parts, some of them do not even have a definite shape. But does this mean that they do not have a skeleton at all?

Jean Baptiste Lamarque once united them into a large group of invertebrates, but apart from the absence of a spine, these animals no longer unite them. It is now known that even single-celled organisms have a skeleton.

For example, in radiolarians, it consists of chitin, silicon, or sulphate of strontium and is located inside the cell. In corals, the skeleton can be hydrostatic, internal proteinaceous or external limestone. Worms, jellyfish and some mollusks are hydrostatic.

In a number of mollusks, the skeleton is external and has the shape of a shell. Different types of its structure is different. Typically, it includes three layers consisting of the protein conchiolin and calcium carbonate. Shells are bivalves (mussels, oysters) and spiral with curls, and sometimes carbonate needles and thorns.

Arthropods

The type of arthropods also refers to invertebrates. This is the most numerous group of animals that unites crustaceans, arachnids, insects, millipedes. Their body is symmetrical, has paired limbs and is divided into segments.

The structure of the skeleton of animals is external. It covers the entire body in the form of a cuticle containing chitin. Cuticle is a hard shell protecting every segment of the animal. Its dense patches are sclerite, connected by more flexible and flexible membranes.

The insects of the cuticle are firm and thick, and consist of three layers. On the surface it forms hairs (heta), thorns, setae and various outgrowths. The arachnid cuticle is relatively thin and contains under itself a skin layer and basal membranes. In addition to protection, it protects animals from loss of moisture.

Land crabs and woodworms do not have an outer dense layer, which retains moisture in the body. From drying out, they save only the way of life - animals constantly seek places with high humidity.

Skeleton of chordates

Chorda is an internal axial skeletal formation, a longitudinal bony framework of the body. It is present in chordates, which number more than 40 000 species. These include invertebrates, in which the chord is present a certain period in one of the stages of development.

In the lower representatives of the group (lancelets, cyclostomes and individual fish species), the chord is preserved throughout life. In lancelets, it is located between the intestine and the neural tube. It consists of transverse muscle plates, which are surrounded by a membrane and are joined together by outgrowths. Cutting and relaxing, it works like a hydrostatic skeleton.

In the Cyclostrida, the chord is harder and has rudiments of the vertebrae. They do not have paired limbs, jaws. The skeleton is formed only by connective and cartilaginous tissue. Of these, the skull is formed, the rays of the fins and the openwork lattice of the gills of the animal. The tongue of the crescent also has a skeleton; on the top of the organ is a tooth, with which the animal digests prey.

Vertebrates

In the higher representatives of the chordates, the axial cord is transformed into a spine, a supporting element of the inner skeleton. It is a flexible pillar consisting of bones (vertebrae), which are connected by discs and cartilages. As a rule, it is divided into departments.

The structure of skeletons of vertebrate animals is considerably complicated, in comparison with other chordates and, moreover, with invertebrates. For all members of the group is characterized by the presence of an internal framework. With the development of the nervous system and the brain, they formed a bone cranium. And the appearance of the spine provided better protection of the spinal cord and nerves.

The paired and unpaired limbs depart from the spine. Unpaired tails and fins, paired divide into the belts (upper and lower) and the skeleton of free limbs (fins or five-fingered limbs).

Fish

In these vertebrate animals, the skeleton consists of two sections: the trunk and the caudal. Sharks, rays and chimeras do not have bone tissue. Their skeleton is made up of flexible cartilages, which eventually accumulate lime and become firmer.

The rest of the fish have a bone skeleton. Cartilage layers are located between the vertebrae. In the anterior part, lateral processes extend from them to the ribs. The skull of fish, in contrast to terrestrial animals, has more than forty moving elements.

The pharynx is surrounded by a semicircle from 3 to 7 gill arches, between which are located gill slits. On the outside they form gills. They are in all fish, only in some they are formed by cartilaginous tissue, and in others - by bone.

From the spine depart radial bones of fins connected by the membrane. Pairt fins - thoracic and ventral, unpaired - anal, dorsal, caudal. Their number and type vary.

Amphibians and reptiles

Amphibians have cervical and sacral parts, which range from 7 to 200 vertebrae. Some amphibians have a tail section, some have no tail, but there are paired extremities. They move with jumps, so the hind legs are lengthened.

In tailless species, there are no ribs. The mobility of the head is ensured by the cervical vertebra, which is attached to the occiput. In the thoracic region there are scapula, collarbone, shoulders, forearms, and brushes. In the pelvic department there are iliac, pubic and sciatic bones. And the hind limbs have a shin, hip, foot.

The skeleton of reptiles also has these parts, becoming more complicated with the fifth department of the spine - lumbar. They have from 50 to 435 vertebrae. The skull is more ossified. The tail section is necessarily present, its vertebrae diminish towards the end.

Turtles have an exoskeleton in the form of a durable shell of keratin and an inner bone layer. The jaws of turtles are deprived of teeth. Snakes do not have sternum, shoulder and pelvic girdle, and ribs are attached along the entire length of the spine, except for the caudal region. Their jaws are connected very tightly to swallow large prey.

Birds

Features of the skeleton of birds are largely related to their ability to fly, some species have adaptations for running, diving, climbing along branches and vertical surfaces. Birds have five departments of the spine. Parts of the cervical region are connected movably, in the remaining parts of the vertebra often fused.

Their bones are light, and some are partially filled with air. The neck of the birds is elongated (10-15 vertebrae). Their skull is holistic, without seams, in the front part has a beak. The shape and length of the beak are very different and are related to the way animals are fed.

The main device for flying is the keel. This is the bone growth in the lower part of the sternum, to which the pectoral muscles are attached. Kiel is developed in flying birds and penguins. In the structure of the skeleton of vertebrates associated with flight or digging (moles and bats), it is also present. He does not have ostriches, an owl parrot.

The forelimbs of the birds are wings. They consist of a thick and strong humerus, a curved ulnar and a thin radial. In the brush, some bones are fused together. In all, except ostriches, pelvic pubic bones do not fuse with each other. So birds can lay large eggs.

Mammals

Now there are about 5 500 species of mammals, including man. In all members of the class, the inner skeleton is divided into five divisions and includes the skull, the vertebral column, the thorax, the belts of the upper and lower extremities. Battleships have an exoskeleton in the form of a shell of several shields.

The cranium of the mammals is larger, there is a zygomatic bone, a secondary skeleton of the palate and a paired drum bone, which is not found in other animals. The upper belt, mainly includes the shoulder blades, collarbone, shoulder, forearm and hand (from the wrist, pastern, fingers with phalanges). The lower belt consists of the thigh, shin, foot with the tarsus, plus and fingers. The greatest differences within the class are visible in the belts of the limbs.

Dogs and solipeds have no scapula and clavicles. Seals of the humeral and femoral parts are hidden inside the body, and the five-fingered limbs are connected by a membrane and look like fins. Bats fly like birds. Their fingers (except one) are strongly elongated and connected by a webbed of skin, forming a wing.

What is the difference between a person?

The human skeleton has the same parts as other mammals. In structure, it is most similar to chimpanzees. But, unlike them, a man's legs are much longer than his hands. The entire body is oriented vertically, the head does not protrude forward, as in animals.

The proportion of the skull in the structure is much larger than that of the monkeys. The jaw apparatus, on the contrary, is smaller and shorter, the fangs are reduced, the teeth are covered with protective enamel. A person has a chin, a skull rounded, has no continuous superciliary arches.

We do not have a tail. Its underdeveloped version is represented by a coccyx from 4-5 vertebrae. Unlike mammals, the thorax is not flattened from both sides, but is enlarged. The thumb is opposed to the rest, the wrist moves together with the wrist.