The 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 are the differences? What is the difference between the human skeleton and the structure of other mammals?
The skeleton is the support of the body
The solid and elastic structure of bones, cartilage and ligaments in the body of humans and animals is called the skeleton. Together with the muscles and tendons, it forms the musculoskeletal 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 "frame" of the body does not always consist of bone and cartilage, sometimes it is formed by chitin, keratin or even limestone.
The amazing component of the body is the bones. They are very durable and tough, able to withstand huge loads, but at the same time remain light. In a young body, bones are elastic, and over time become more fragile and brittle.
The skeleton of animals is a kind of "pantry" of mineral substances. If the body lacks them, then the balance of the necessary elements is replenished from the bones. Bones are made up of water, fat, organic matter (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 humans and animals is the shell inside which the internal organs are located. The skeleton gives shape to this shell. Muscles and tendons are attached directly to it, contracting, they bend the joints, carrying out movement. So, we can raise our legs, turn our heads, sit down or hold something with our hand.
In addition, the skeleton of animals and humans serves as protection for soft tissues and organs. For example, the ribs hide the lungs and heart underneath, blocking them from the blows (of course, if the blows are not too powerful). The skull prevents a rather fragile brain from damage.
Some bones contain one of the most important organs - the bone marrow. In humans, he participates in the processes of hematopoiesis, forming red blood cells. It also forms white blood cells - white blood cells that are responsible for the body's immunity.
How and when did the skeleton originate?
The skeleton of animals and the entire musculoskeletal system arose due to 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 amoebic soft-bodied creatures.
Then in the atmosphere and hydrosphere of the planet was ten times less oxygen. At some point, the proportion of gas began to increase, triggering, as scientists suggest, a chain reaction of changes. So, in the mineral composition of the ocean, the number of calcites and aragonites increased. They, in turn, accumulated in living organisms, forming solid or elastic structures.
The earliest organisms that possessed a skeleton were found in the strata of limestone rocks in Namibia, Siberia, Spain and other regions. They inhabited the oceans around 560 million years ago. In their structure, organisms resembled sponges with a cylindrical body. Long rays radiated from them (up to 40 cm) from calcium carbonate, which served as the skeleton.
Types of skeletons
In the animal world , three types of skeleton are distinguished: external, internal and liquid. The external or exoskeleton is not hidden under the skin or other tissues, but completely or partially covers the body of the animal from the outside. Which animals have an external skeleton? They are possessed by arachnids, insects, crustaceans, as well as some vertebrates.
Like armor, it performs mainly a protective function, and sometimes can serve as a refuge for a living organism (shell of turtles or snails). Such a skeleton has a significant drawback. It does not grow with the owner, which is why the animal is forced to periodically dump it and grow a new cover. For some period, the body loses its usual protection and becomes vulnerable.
The endoskeleton is the internal skeleton of animals. It is covered in meat and skin. It has a more complex structure, performs many functions and grows simultaneously with the whole organism. The endoskeleton is divided into the axial part (spine, skull, chest) and additional or peripheral (limbs and bones of the belts).
A fluid or hydrostatic skeleton is the least common. It is possessed by jellyfish, worms, sea anemones, etc. It is a muscle wall filled with fluid. Fluid pressure maintains the shape of the body. With muscle contraction, pressure changes, which sets the body in motion.
Which animals do not have a skeleton?
In the usual sense, the skeleton is precisely the inner frame of the body, the totality of the bones and cartilage that form the skull, limbs, and spine. However, there are a number of organisms that do not possess these parts; some of them do not even have a specific shape. But does this mean that they have no skeleton at all?
Jean Baptiste Lamarck once united them into a large group of invertebrates, but apart from the absence of the spine, these animals no longer have anything in common. It is now known that even single-celled organisms have a skeleton.
For example, in radiolaria, it consists of chitin, silicon or strontium sulfate and is located inside the cell. In corals, the skeleton can be hydrostatic, internal protein or external limestone. In worms, jellyfish and some mollusks, it is hydrostatic.
In a number of mollusks, the skeleton is external and has the shape of a shell. In different species, its structure is different. As a rule, it includes three layers consisting of conchiolin protein and calcium carbonate. Shells are bivalve (mussels, oysters) and spiral with curls, and sometimes carbonate needles and spikes.
Arthropods
The type of arthropod also belongs to invertebrates. This is the most numerous group of animals, which combines 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. The cuticle is a hard shell protecting each segment of the animal. Its dense areas of sclerites are interconnected by more mobile and flexible membranes.
In insects, the cuticle is strong and thick, consists of three layers. On the surface, it forms hairs (hats), spikes, bristles and various outgrowths. In arachnids, the cuticle is relatively thin and contains a skin layer and basement membranes. In addition to protection, it protects animals from moisture loss.
Land crabs and wood lice do not have a dense outer layer that retains moisture in the body. Only a way of life saves them from drying out - animals constantly strive for places with high humidity.
The skeleton of chordates
Chorda is an internal axial skeletal formation, a longitudinal strand of the bone skeleton of the body. Present in chordates, of which there are more than 40,000 species. Among them are invertebrates, in which the chord is present for some period in one of the stages of development.
In the lower representatives of the group (lancelet, cyclostomes and individual species of fish), the chord is maintained throughout life. In lancelettes, it is located between the intestine and neural tube. It consists of transverse muscle plates, which are surrounded by a sheath and are interconnected by outgrowths. By contracting and relaxing, it works like a hydrostatic skeleton.
The cyclostome chord is harder and has primordia of the vertebrae. They have no paired limbs, jaws. The skeleton is formed only by connective and cartilage tissue. From them the skull, rays of the fins and the openwork lattice of the gills of the animal are formed. The tongue of the cyclostomes also has a skeleton, on the top of the organ is a tooth with which the animal drills the prey.
Vertebrates
In higher representatives of the chordate axial cord turns into the spine - the bearing element of the internal skeleton. It is a flexible pillar consisting of bones (vertebrae) that are connected by discs and cartilage. As a rule, it is divided into departments.
The structure of the skeletons of vertebrates is significantly complicated, compared with other chordates and, especially, with invertebrates. All representatives of the group are characterized by the presence of an internal framework. With the development of the nervous system and the brain, they formed a bone cranial box. And the appearance of the spine provided better protection for the spinal cord and nerves.
Paired and unpaired limbs extend from the spine. Unpaired are tails and fins, paired are divided into belts (upper and lower) and the skeleton of the free limbs (fins or five-fingered limbs).
Fish
In these vertebrates, the skeleton consists of two sections: trunk and tail. Sharks, stingrays and chimeras do not have bone tissue. Their skeleton is made of flexible cartilage, which eventually accumulate lime and become harder.
In other fish, the skeleton is bone. Cartilaginous layers are located between the vertebrae. In the front of them lateral processes extending into the ribs depart. The fish skull, unlike terrestrial animals, has more than forty moving elements.
The throat is surrounded by a half-ring from 3 to 7 branchial arches, between which branchial gaps are located. From the outside, they form gills. All fish have them, only some form cartilaginous tissue, while others - bone.
The radial bones of the fins connected by the membrane extend from the spine. Paired fins - pectoral and ventral, unpaired fins - anal, dorsal, caudal. Their number and type vary.
Amphibians and reptiles
Amphibians appear cervical and sacral divisions, which make up from 7 to 200 vertebrae. Some amphibians have a tail section, some do not have a tail, but there are paired limbs. They move in leaps, so the hind limbs are elongated.
Tailless species lack ribs. The mobility of the head provides the cervical vertebra, which is attached to the back of the head. The scapula, collarbone, shoulders, forearms and hands appear in the thoracic region. In the pelvic section there are iliac, pubic and ischial bones. And the hind limbs have a lower leg, thigh, and foot.
The skeleton of reptiles also has these parts, complicated by the fifth lumbar spine. They have from 50 to 435 vertebrae. The skull is more ossified. The tail section is necessarily present, its vertebrae decrease towards the end.
Turtles have an exoskeleton in the form of a durable shell of keratin and the inner bony layer. The jaws of turtles are devoid of teeth. Snakes have no sternum, shoulder and pelvic girdle, and ribs are attached along the entire length of the spine, except for the tail section. Their jaws are connected very fluidly to swallow large prey.
Birds
The 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 sections of the spine. Parts of the cervical spine are connected movably; in the remaining sections, the vertebrae are 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, has a beak in front. The shape and length of the beak are very different and are associated with the way animals are fed.
The main device for flying is the keel. This is a bone outgrowth in the lower part of the sternum, to which the pectoral muscles are attached. Keel 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. Ostriches, an owl parrot do not have it.
The forelimbs of birds are wings. They consist of a thick and strong humerus, a curved ulna and a thin radius. In the brush, some bones fused together. In all but ostriches, the 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 humans. In all members of the class, the internal skeleton is divided into five sections and includes the skull, spinal column, chest, and upper and lower extremity belts. Armadillos have an exoskeleton in the form of a shell of several shields.
The skull of mammals is larger, there is a zygomatic bone, a secondary bone palate and a paired tympanic bone, which other animals do not have. The upper belt, mainly includes the shoulder blades, collarbone, shoulder, forearm and hand (from the wrist, metacarpus, fingers with phalanges). The lower belt consists of the thigh, lower leg, foot with tarsus, metatarsus and toes. The greatest differences within the class are visible precisely in the limb zones.
Dogs and artiodactyls have no shoulder blades and collarbones. In seals, the humerus and femur are hidden inside the body, and the five-fingered limbs are connected by a membrane and look like flippers. Bats fly like birds. Their fingers (except one) are very elongated and connected by a membrane of skin, forming a wing.
How is a person different?
The human skeleton has the same departments as other mammals. In structure, it is most similar to chimpanzees. But, unlike them, a person’s legs are much longer than arms. The whole body is oriented vertically, the head does not protrude forward, as in animals.
The share of the skull in the structure is much larger than that of 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, the skull is rounded, does not have continuous superciliary arches.
We have no tail. Its underdeveloped version is represented by a coccyx of 4-5 vertebrae. Unlike mammals, the chest is not flattened on two sides, but expanded. The thumb is opposed to the rest, the hand is movably connected to the wrist.