Characteristics Of Reptiles

• The integument (skin) of reptiles is covered with epidermal scales.
• Reptiles have a large bony plate called scutes.
• Some reptiles like lizards, crocodiles, etc. have limbs whereas some species, like snakes, don’t.
• Most of the reptilians have movable eye lids. 

• The axial muscles play an important role in both respiration and locomotion.
• Reptiles use lungs for respiration. Though some species, like turtles, have air-permeable skin, they can only supplement lungs.
• Diaphragm is absent in reptiles. However, Tegu lizards possess a proto-diaphragm, a muscular structure which separates the pulmonary cavity from the visceral cavity.
• Most of the reptilians lack secondary plate, an anatomical structure that divides the nasal cavity (cavity of nose) from the oral cavity (mouth). Thus, these reptiles must hold their breath while swallowing food. However, crocodiles have secondary plates. This structure protects their brain from getting damaged while attacking the prey.
• Most of the reptiles have three-chambered heart with two atria and one ventricle. Crocodiles are exceptions; they have four-chambered hearts. Oxygenated blood is carried by two major aortas and then circulated all over the body.
• Reptiles have two small kidneys which excrete nitrogenous wastes.
• They have simple and short digestive tracts.
• Reptilian nervous system, like the amphibians, consists of brain, spinal cord and sensory nerves that run all over the body. However, some parts of brain, like the cerebrum and cerebellum, are larger than the amphibians.
• Reptiles have twelve pairs of cranial nerves. 

• Some species of lizards employ buccal pumping, a characteristic feature found in class amphibia. Buccal pumping is a respiratory method in which the animals move the floor of its mouth (buccal floor) in a rhythmic manner, thus allowing the respiratory gas to enter the lungs.
• Normally, oxygenated blood gets circulated all over the body and deoxygenated blood is carried back to heart. However, under specific conditions, deoxygenated blood can also be shunted to the body and oxygenated blood can be shunted back to lungs.
• Reptiles are not warm-blooded. They often depend on external sources of heat rather than regulating temperature by adjusting their metabolic rates.
• The optimum body temperature varies according to the species. However, it is typically lesser than that of warm-blooded animals, except for American desert iguana, which has a body temperature of 35–40°C, thus reaching mammalian range. The body temperature of lizards, typical reptiles, ranges from 24–35°C.
• Reptiles have low resting metabolism which helps them spend less energy to sustain life activities and thereby enables them to conserve energy.
• Reptiles are unable to produce highly concentrated urine. This is because they lack Henle’s loop, a structure which is present in mammalian kidney.
• Reptiles use colon, part of their intestine, for the reabsorption of water. However, some reptiles can reabsorb water from the bladder also. They have nasal and lingual salt glands to excrete excess salt.
• Digestion is a slow process for reptiles. This is because of their lower resting metabolic rate and their inability to chew food.
• Reptiles are predominantly carnivorous, except for some herbivorous species like turtles.
• Lack of complex teeth lead to the inability to chew food and hence, some herbivorous reptiles swallow rocks and pebbles to aid churning of food.
• Most of the reptilians are adapted to see in daylight. They have a more advanced color vision than amphibians. However, in some species like the blind snake, vision is considerably reduced.
• Some snakes like pit vipers, boas and pythons have specialized visual organs (pits) that are sensitive to infrared radiations. These pits help them identify the presence of their warm-blooded prey like birds and mammals. 

• Reptiles lay eggs which are protected by membranes and calcareous shell. 
• Fertilization is internal i.e., eggs get fertilized inside the female.
• Reptiles generally reproduce sexually. However, some species may reproduce asexually too.
• Most reptiles have well-developed copulatory organs, which are generally retracted into the body. However, Tuataras lack copulatory organs and hence, they just press their cloacas (reproductive organ) against each other. 

The origin of reptiles is traced back to millions of years and they have been undergoing evolutionary changes since then. The characteristics mentioned above are generic and can vary according to the species.