The skeletons of different animals are different from each other. Their structure largely depends on the habitat and lifestyle of a particular organism. What do animal skeletons have in common? What differences exist? How is the human skeleton different from that of other mammals?
The skeleton is the support of the body
The hard and elastic structure of bones, cartilage and ligaments in the human and animal body is called the skeleton. Together with muscles and tendons, it forms the musculoskeletal system, thanks to which living beings can move in space.
It mainly 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 cartilage tissue, sometimes it is formed by chitin, keratin or even limestone.
An amazing part of the body is the bones. They are very strong and rigid, 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 minerals. If athe body lacks them, then the balance of the necessary elements is replenished from the bones. Bones consist of water, fat, organic substances (polysaccharides, collagen), as well as s alts of calcium, sodium, phosphorus, and magnesium. The exact chemical composition depends on the nutrition of a particular organism.
Meaning of the skeleton
The body of people and animals is a shell, inside of which there are internal organs. This shell is shaped by the skeleton. Muscles and tendons are attached directly to it, contracting, they bend the joints, making movement. So, we can lift a leg, turn our head, 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 under them, covering them from blows (of course, if the blows are not too powerful). The skull prevents damage to the rather fragile brain.
Some bones contain one of the most important organs - the bone marrow. In humans, it is involved in the processes of hematopoiesis, forming red blood cells. It also forms leukocytes, white blood cells that are responsible for the body's immunity.
How and when did the skeleton come about?
The skeleton of animals and the entire musculoskeletal system arose thanks 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, soft-bodied amoebic creatures existed on our planet.
Then in the atmosphere and hydrosphere of the planet there was ten times less oxygen. At some point, the share of gas becameincrease, starting, as scientists suggest, a chain reaction of changes. Thus, the amount of calcites and aragonites increased in the mineral composition of the ocean. They, in turn, accumulated in living organisms, forming solid or elastic structures.
The earliest organisms that had a skeleton were found in limestone strata in Namibia, Siberia, Spain and other regions. They inhabited the world's oceans about 560 million years ago. In their structure, the organisms resembled sponges with a cylindrical body. Long rays (up to 40 cm) of calcium carbonate departed radially from them, which played the role of a skeleton.
Varieties of Skeletons
In the animal world, there are three types of skeleton: external, internal and liquid. The external or exoskeleton is not hidden under the cover of skin or other tissues, but completely or partially covers the body of the animal from the outside. What animals have an external skeleton? It is possessed by arachnids, insects, crustaceans, and some vertebrates.
Like armor, it performs mainly a protective function, and sometimes it can serve as a shelter for a living organism (tortoise or snail shell). Such a skeleton has a significant drawback. It does not grow with the owner, which is why the animal is forced to periodically shed 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 leather. It has a more complex design, performs many functions and growssimultaneously with the whole organism. The endoskeleton is divided into an axial part (spine, skull, chest) and an additional or peripheral part (limbs and bones of the belts).
The liquid or hydrostatic skeleton is the least common. It is possessed by jellyfish, worms, sea anemones, etc. It is a muscular wall filled with liquid. Fluid pressure maintains the body's shape. When muscles contract, pressure changes, which sets the body in motion.
What animals don't have a skeleton?
In the usual sense, the skeleton is precisely the internal frame of the body, a set of 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 which do not even have a specific shape. But does that mean they don't have a skeleton at all?
Jean Baptiste Lamarck once united them into a large group of invertebrates, but apart from the absence of a backbone, nothing else unites these animals. It is now known that even single-celled organisms have a skeleton.
For example, in radiolarians it consists of chitin, silicon or strontium sulfate and is located inside the cell. Corals can have a hydrostatic skeleton, an internal protein, or an external calcareous skeleton. In worms, jellyfish and some molluscs, 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 the protein conchiolin and calcium carbonate. Shells are bivalve (mussels, oysters) and spiralwith curls and sometimes carbonate needles and spikes.
Arthropods
The type of arthropod also belongs to the invertebrates. This is the most numerous group of animals, which includes crustaceans, arachnids, insects, centipedes. Their body is symmetrical, has paired limbs and is divided into segments.
By structure, 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 that protects each segment of the animal. Its dense areas are sclerites, 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 (chaetae), spikes, bristles and various outgrowths. In arachnids, the cuticle is relatively thin and contains a dermal layer and basement membranes underneath. In addition to protection, it prevents animals from losing moisture.
Land crabs and wood lice do not have a dense outer layer that retains moisture in the body. Only the way of life saves them from drying out - animals constantly strive for places with high humidity.
Skeleton of chordates
Chord is an internal axial skeletal formation, a longitudinal strand of the bone frame of the body. It is present in chordates, of which there are more than 40,000 species. These include invertebrates, in which the notochord is present for a certain period in one of the stages of development.
In the lower representatives of the group (lancelets, cyclostomesand certain species of fish) the notochord persists throughout life. In lancelets, it is located between the intestines and the neural tube. It consists of transverse muscle plates, which are surrounded by a shell and are interconnected by outgrowths. Contracting and relaxing, it works like a hydrostatic skeleton.
In cyclostomes, the notochord is more solid and has rudiments of vertebrae. They do not have paired limbs, jaws. The skeleton is formed only by connective and cartilaginous tissue. Of these, the skull, rays of the fins and the openwork lattice of the gills of the animal are formed. The tongue of cyclostomes also has a skeleton; at the top of the organ there is a tooth, with which the animal bores its prey.
Vertebrates
In the higher representatives of the chordates, the axial cord turns into a spine - the supporting element of the internal skeleton. It is a flexible column 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 much more complicated than that of other chordates and, moreover, of invertebrates. All representatives of the group are characterized by the presence of an internal frame. With the development of the nervous system and brain, they formed a bone cranium. And the appearance of the spine provided better protection for the spinal cord and nerves.
Paired and unpaired limbs depart from the spine. Unpaired ones are tails and fins, paired ones are divided into belts (upper and lower) and a skeleton of free limbs (fins or five-fingered limbs).
Pisces
TheseIn vertebrates, the skeleton consists of two sections: the trunk and tail. Sharks, rays and chimeras do not have bone tissue. Their skeleton is made up of flexible cartilage that accumulates lime and becomes hard over time.
The rest of the fish have a bone skeleton. Cartilaginous layers are located between the vertebrae. In the anterior part, lateral processes extend from them, passing into the ribs. The skull of fish, unlike land animals, has more than forty moving parts.
The pharynx is surrounded by a semicircle from 3 to 7 gill arches, between which gill slits are located. On the outside, they form gills. All fish have them, only in some they are formed by cartilaginous tissue, while in others - by bone.
The radius bones of the fins, connected by a membrane, depart from the spine. Paired fins - pectoral and ventral, unpaired - anal, dorsal, caudal. Their number and type vary.
Amphibians and reptiles
Amphibians have cervical and sacral sections, which range from 7 to 200 vertebrae. Some amphibians have a tail section, some do not have a tail, but there are paired limbs. They move by jumping, so the hind limbs are elongated.
Tailless species lack ribs. The mobility of the head is provided by the cervical vertebra, which is attached to the back of the head. Shoulders, forearms and hands appear in the thoracic region. The pelvis contains the iliac, pubic, and ischial bones. And the hind limbs have a lower leg, thigh, foot.
Reptile skeleton toohas these parts, becoming more complicated with the fifth section of the spine - the lumbar. They have 50 to 435 vertebrae. The skull is more ossified. The tail section is always present, its vertebrae decrease towards the end.
Turtles have an exoskeleton in the form of a strong shell of keratin and an inner layer of bone. The jaws of turtles are devoid of teeth. Snakes do not have a sternum, shoulder and pelvic girdle, and the ribs are attached along the entire length of the spine, except for the tail section. Their jaws are very flexible 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 branches and vertical surfaces. Birds have five sections of the spine. Parts of the cervical region are connected movably, in other departments the vertebrae are often fused.
Their bones are light and some are partially filled with air. The neck of birds is elongated (10-15 vertebrae). Their skull is complete, without seams, in front of it has a beak. The shape and length of the beak are very different and are related to the way animals feed.
The main device for flight is the keel. This is a bony outgrowth in the lower part of the sternum, to which the pectoral muscles are attached. The 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. The ostriches don't have it, the owl parrot.
The forelimbs of birds are wings. They consistfrom a thick and strong humerus, a curved ulna and a thin radius. Some of the bones in the hand are fused together. In all but ostriches, the pelvic pubic bones do not fuse together. This is how 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, vertebral column, chest, belts of the upper and lower extremities. 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 bony palate and a paired tympanic bone, which is not found in other animals. The upper belt, mainly includes the shoulder blades, collarbones, 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 fingers. The greatest differences within the class are seen precisely in the limb belts.
Dogs and equids lack shoulder blades and clavicles. In seals, the shoulder 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 web of skin, forming a wing.
How is a person different?
The human skeleton has the same sections as other mammals. In structure, it is most similar to a chimpanzee. But, unlike them, human legs are much longer than arms. The whole body is orientedvertically, 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. The person has a chin, the skull is rounded, has no continuous brow ridges.
We don't have a tail. Its underdeveloped variant is represented by a coccyx of 4-5 vertebrae. Unlike mammals, the chest is not flattened on both sides, but expanded. The thumb is opposed to the rest, the hand is movably connected to the wrist.
