TOPIC 9: REPTILES
These are terrestrial vertebrates which are poikilothermic and their bodies are covered in dry scales. They have internal fertilization and external development of eggs; so they are oviparous.
Only a few are viviparous i.e. produce young ones live for example the viper snake.
An Indian Crocodile
Their two pairs of pentadactyl limbs do not support the body off the ground. Snakes do not have limbs.
Reptiles have identical teeth and so are homodont.
They breathe using lungs.
The extinct reptiles include the dinosaurs.
Although some reptiles look like amphibians, their lives are different. The most important difference between reptiles and amphibians is that reptiles do not breed in water and they have covering scales.
Crocodiles, turtles and some snakes spend a lot of time in water but they cannot die when not in water as fish do neither do they breed in water as amphibians do.
In living on land reptiles prevent water loss from their bodies by:
- Having a skin with dry scales.
- Excreting dry uric acid crystals;
- Absorbing water in the body using the kidneys and the rectum.
The lizard:
Unlike the toad the lizard has got a neck, a tail and scales on its body.
It has no sweat glands.
Lizards have got five digits on all limbs unlike in the toad where the fore limbs have four digits.
Lizards do not have a diaphragm.
Like fish, amphibians and birds, lizards' blood has got red blood cells which have a nucleus.
Lizards excrete solid and dry uric crystals as its nitrogenous waste products.
The male is usually more attractive especially during mating season.
The male lizard has got two penes (plural for penis) which enter the cloaca up to the entry to the two oviducts to inject sperm into the female i.e. internal fertilization.
Eggs are laid in sand.
A lizard lays 5-8 soft-shelled eggs which hatch after eight weeks.
Full maturity is reached after two years.
Crocodiles
Lesson Summary
- Reptiles are air-breathing, cold-blooded vertebrates characterized by a scaly skin.
- Reptiles have a variety of reproductive systems, with different strategies for providing nutrition to developing young.
- Lizards and snakes are distinguished by a unique type of scaly skin and movable quadrate bones.
- Lizards have some unique adaptations, including regeneration of lost limbs or tails and changing color.
- Snakes are distinguished by lack of eyelids, limbs, external ears and vestiges of forelimbs.
- Snakes have various adaptations for killing and eating their prey.
- Crocodilia have a flexible semi-erect posture, lifelong replacement of teeth, and a secondary bony palate.
- The sex of developing crocodilians is determined by the incubation temperature of the eggs.
- Other crocodilian traits, such as salt glands, nictitating membranes, ear flaps, and sensory pits, are adaptations for aquatic living.
- Turtles are characterized by a special bony or cartilaginous shell. They have specialized adaptations for aquatic living, such as eye placement and salt glands, and adaptations for terrestrial living as well, like placement of eyes and protection of eggs.
- Reptiles play important roles as predators of pest species, food sources, pets, in medical and scientific research, and in folklore, religion and popular culture.
Review Questions
Recall
1. Describe three general traits of reptiles.
2. Describe two different types of reproduction in reptiles.
3. How are snakes different from legless lizards?
Apply Concepts
4. Name two adaptations of a crocodilian stomach which help it in digestion.
5. Name two organs that a turtle or a snake have that closely resemble organs in humans. Why are they similar?
Critical Thinking
6. The shape and structure of a turtle's shell can give its inhabitant advantages for avoiding predators, aid in swimming and diving, and for walking on land. Given what you know about a turtle's shell, explain how the structure and shape could help the turtle in the above situations.