The class Reptiles, or Reptiles, has about 6 thousand species. These are real land animals, which, unlike Amphibians, do not have a close connection with water.
External structure of reptiles
The body of reptiles is divided into sections – head, trunk, tail and two pairs of limbs. The limbs are located on the sides of the body and are pressed to the ground (as if they are close to the surface), which is why this class received such a name – reptiles.
The skin is dry and contains no glands. The skin is formed by the keratinized epidermis (horny scales, or scutes). Horny scales protect the animal from moisture evaporation and desiccation.
Reptiles grow during periodic molts.
The first reptiles appeared on the planet about 280 million years ago.
Stegocephals, ancient amphibians, are considered their ancestors.
The development and flourishing of reptiles is associated with a change in climatic conditions: in the Mesozoic era, it becomes drier, the number of wetlands decreases.
In the new conditions, those amphibians that did not have a close connection with water gained advantage. The first reptiles came from such ancient amphibians.
New traits introduced in reptiles (compared to amphibians) are listed below.
- Dry skin, without glands, covered with horny scales;
- the emergence of a partial, and in crocodiles a complete septum in the ventricle of the heart, which led to a partial separation of the flows of venous and arterial blood;
- the emergence of cellular lungs with developed airways;
- the emergence of protective shells around the egg;
- internal fertilization;
- direct development.
Changes such as the enlargement of the anterior part of the brain and the appearance of the primary cortex in it were also important for life on land.
Reptiles flourished 225 million years ago. They populated all habitats.
Plesiosaurs – “sea lizards” and ichthyosaurs – “fish lizard” swam in the water.
Pterosaurs – “flying dinosaurs” soared in the air.
Various dinosaurs reigned among land animals – “terrible lizards”.
The most ancient reptiles that have survived to this day are crocodiles and turtles.
One of the groups of lizards – the Tooth-toothed lizards – are considered a transitional form between reptiles and mammals. The most famous animal-toothed lizard is Inostrantsevia.
The value of reptiles
- They destroy insects and rodents, regulating their numbers;
- eaten by humans;
- leather and shells are used to make various products;
- snake venom is used in pharmacology.