The skeleton provides structural support to the body of animals, helps in locomotion and protects internal organs. Animals possess varied types of skeletons according to their body organisation, complexity and habitats. The endoskeletons of humans and other animals, such as bats, whales, etc. show marked similarities due to evolution from common ancestors. Invertebrates, such as arthropods possess a chitinous exoskeleton, the body of sponges is supported by spongin fibres or spicules and corals have a calcium carbonate skeleton.
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Similarities and Differences between Human and Animal Skeletons
Let us learn about the similarities and differences between the human skeleton and the skeleton of other animals.
Similarities Between Human and Animal Skeletons:
- The skeleton of humans, as well as other animals, provides structural support and helps in locomotion. It also helps in protecting delicate internal organs and soft tissues.
- Like other vertebrates, humans have an endoskeleton made up of bones and cartilage.
- The basic structure of the vertebrate endoskeletons is quite similar, irrespective of the action they perform, e.g. the forelimbs of a horse, cats, patagium of bats, flippers of whales, wings of birds and hands of humans, etc. all have similar endoskeleton structures. These are called homologous structures and they show common descent.
- The skeleton of vertebrates is divided into axial and appendicular skeletons. The axial skeleton comprises the skull and vertebral column, which forms the main axis and protects the internal organs. The appendicular skeleton comprises limbs and girdles that help in movement and locomotion.
Difference Between Human and Animal Skeletons:
- Humans have endoskeletons, whereas animals have various types of skeletons such as endoskeleton, exoskeleton and hydrostatic skeleton.
- An adult human has 206 bones. The number of bones and muscles varies in different animals.
- The human skeletal system is made up of bones and a few cartilages, whereas some animals possess an endoskeleton made up of cartilages only, e.g. marine cartilaginous fishes (Chondrichthyes), Scoliodon and Pristis.
- The long bones of birds are pneumatic, i.e. hollow with air cavities that aid in flying. Humans do not have pneumatic bones.
- Some organisms with exoskeletons undergo periodic moulting and shed off their exoskeleton many times during their growth. In humans, the growth of the skeleton stops at maturity and maintains a steady state.
Let us now explore a bit more about various types of skeletons present in humans and other animals.
Human Skeleton
The skeletal system of humans is made up of bones and a few cartilages. Bones and cartilage are types of connective tissues. Bones are made up of a hard matrix of calcium salts and the matrix of cartilage is made up of chondroitin salts that make cartilage flexible. An adult human contains 206 bones. The skeleton of humans can be divided into two sections, viz., axial skeleton and appendicular skeleton.
- Axial skeleton – It comprises 80 bones and includes skull, sternum, vertebral column and ribs.
- Appendicular skeleton – It includes limbs, pectoral and pelvic girdles.
The two bones articulate with each other through various types of joints, namely, fibrous, cartilaginous and synovial. Fibrous joints are immovable and present in the skull. Cartilaginous joints allow limited movement and are present in the vertebral column. Synovial joints permit considerable movement and are present in limbs. Ligaments hold two bones together and tendons join a muscle to the bone. Skeletal muscles are associated with bones and cartilages. They are striated and voluntary muscles. They help in movement and locomotion.
Different Types of Skeleton Present in Animals
There are three main types of skeletons found in animals. They are exoskeleton, endoskeleton and hydrostatic skeleton.
Exoskeleton
As the name suggests, the exoskeleton is present externally. It is present in many invertebrates such as arthropods, molluscs, etc. The exoskeleton of arthropods is chitinous and it undergoes moulting. The shell of molluscs is calcareous.
Endoskeleton
Endoskeleton is present in echinoderms and chordates. It provides support internally. It is composed of mineralised tissue. It consists of bones and cartilage. Some of the bones have bone marrow that is the site of synthesis of blood cells, i.e. haematopoiesis.
Hydrostatic Skeleton
A hydrostatic skeleton or hydroskeleton is a type of flexible skeleton. Here the hydrostatic pressure present inside the body fluid provides the structural support. It comprises fluid-filled coelom supported by longitudinal and circular muscles, which aid in the movement of organisms and provide a definite shape. A hydrostatic skeleton is present in many invertebrates, such as starfish (echinoderms), jellyfish (coelenterates), sea anemones, etc.
Characteristics of Skeleton in Animals
Below is a list of some of the animals and types of skeletons present in them:
- Sponges – The skeleton is made up of spongin fibres called spicules.
- Cnidarians – Corals have a calcareous exoskeleton. Hydra and sea anemone have a hydrostatic skeleton.
- Earthworms – The body of earthworms is supported by a hydrostatic skeleton.
- Arthropods – They have chitinous exoskeleton
- Echinoderms – They have a calcareous endoskeleton. They possess calcareous ossicles.
- Birds – The bones of birds are adapted for flight.
- Fish – Fish have endoskeletons made up of bones or cartilage.
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