Reptiles like chameleons and coral snakes are a popular choice as pets. They have many unique adaptations that make them a good fit for indoor or outdoor habitats.
The key difference between reptiles and amphibians is that they have lungs instead of gills. They also have dry scaly skin, highly efficient kidneys and terrestrially adapted eggs that are protected by membranes (amnion and chorion). They are not restricted to water habitats like amphibians.
Scaly Skin
The outer covering of reptiles is made of overlapping, tough scales. They help protect the animals from injury and loss of water. The scales are composed of a substance called keratin. Reptiles with scaly skin also have few glands, compared to amphibians and mammals.
A reptile’s ability to float on water enabled it to survive in environments where other vertebrates can’t. It’s this ability that allows some reptiles, like crocodiles and alligators, to eat fish from the surface of water.
When a reptile displays aggression, it may puff up its lungs and hiss air out in a display that increases its size and warns a predator to back off. This behavior is common in many snakes including pipe snakes (Anilliidae), rat snakes (Uropeltidae) and ring necked snakes (Colubridae). A hissing reptile’s lungs also serve to amplify the sound, making it louder.
Reptiles were the first vertebrates to separate from aquatic environments, and they’ve developed a number of physical adaptations to enable them to live completely on land. For example, most reptiles have lost their limb bones, except for a few types that have evolved into fins or flippers. This has allowed them to conserve energy.
Highly Efficient Kidneys
Reptiles, which are the class Reptilia, have many traits that make them well suited to their habitats. These adaptations — structural features and behavioral strategies — help them thrive in their environments.
A key reptile adaptation is dry scaly skin, which prevents their internal fluids from evaporating. This is a shift from their amphibian ancestors, which had wet skin.
Another important reptile adaptation is lungs that replaced gills when they moved to land. Amphibians need gills to survive in water, but reptiles can use their lungs to breathe on land and have no need for temporary gills like those of frogs.
Each kidney has about a million functioning units called nephrons. They work together to filter blood and remove wastes from the body. They also adjust the amounts of chemicals and water added to the body to keep a balance of fluids.
Kidneys are remarkable organs that can cope with changes in the environment, such as low blood pressure. They can also shut down in serious health emergencies to protect the body’s tissues. They can restart later as conditions improve, although some medicines and some diseases can injure the kidneys, which can have serious consequences.
Reptiles can get the water they need from their food, but some of them live in dry areas where getting enough water is challenging. They can also conserve water by reducing the amount of urine they produce. Sea snakes and file snakes, for example, have a gland that excretes excess salts when they shed.
Laying Eggs That Can Survive on Land
The development of scaly skin was a key adaptation that allowed reptiles to move away from aquatic environments. It reduces water loss and keeps internal fluids intact. This occlusive skin also prevents amphibians, like frogs, from using their skin for respiration and allows reptiles to breathe through their lungs. This ability to live on land is one of the key characteristics that separates reptiles from other tetrapods, including fish and amphibians. The other is laying shelled eggs. Together, these traits allow reptiles to complete their life cycles on land and explore drier habitats.
Reptiles, birds and mammals make up the clade of vertebrates called amniotes, which have evolved to lay eggs with a protective shell. These eggs are a key feature that distinguishes them from amphibians and other non-amniotes, which must return to water to lay their eggs.
Amphibians lay jelly-like eggs, which are not able to survive in the dry environment of the terrestrial world. The evolution of shelled eggs allowed amniotes to occupy drier, arid habitats.
Many reptiles today, such as snakes, lizards and crocodiles, lay eggs enclosed in a hard shell. However, they still reproduce sexually by internal fertilization. Some species, such as sea turtles, are ovoviviparous, meaning that they rely on their mother to lay the eggs and keep them at the correct temperature. Other reptiles, such as birds, give birth to their young alive, rather than laying eggs. Birds have a sharp area near the tip of their beak, called an egg tooth, that hatching babies use to pierce the shell when they’re ready to enter the world.
Ectothermic Adaptations
Unlike endotherms, ectotherms cannot generate internal heat and must instead rely on ambient conditions for their operating body temperatures. This can make achieving and maintaining their optimum body temperatures challenging, especially in habitats with varying weather patterns.
Ectotherms have developed many behavioral adaptations to help regulate their body temperature. They can burrow into the ground, lie in the sun to bask and even change their colors to absorb different wavelengths of sunlight, depending on the situation. During periods of excessive heat, they can release proteins called heat-shock proteins to prevent the denaturing of other vital proteins.
In colder environments, ectotherms can develop freeze tolerance to protect their tissues from freezing. To do this, they manufacture and flood their cells and tissues with cryoprotectants such as sugars, glycerol and sorbitol. They also eliminate any potent ice-nucleating agents, such as inorganic particulates, microorganisms and proteins that can organize water molecules into a crystalline structure.
In addition, some ectotherms can achieve a state of torpor in which their metabolism slows or, as in the case of wood frogs, even stops altogether. Torpor can last overnight, a season or even years. It is a remarkable survival strategy that can only be achieved by a large number of specialized biochemical and physiological responses, such as alterations in membrane and protein structure and the ability to suppress metabolism (Costanzo et al., 2001).