Marine reptiles require specific habitats such as coral reefs and seagrass beds to survive. Habitat loss and degradation are major concerns for their conservation.
Reptiles are ectothermic tetrapods that lay eggs enclosed in shells, but some species are ovoviviparous and give birth to live young. Their impermeable scaly skin reduces water loss; however, they cannot use their skin for respiration as amphibians can, and they all breathe with lungs.
Reptiles are a group of vertebrates, or animals with a backbone, that include turtles, snakes, lizards and crocodilians. They have dry scaly skin and hard bony skeletons. They were the dominant land animal group for over 250 million years until the extinction of dinosaurs and the rise of mammals.
A key adaptation that allowed reptiles to survive on land was the evolution of amniotic eggs. Unlike the soft, gelatinous eggs of amphibians and fish, amniotic eggs allow embryos to grow inside protective sacs and shells until they are mature enough to live on dry land.
Most reptiles also have thick, waterproof skin. This is not to keep water out, but rather to help conserve moisture inside their bodies. This helps them survive in dry, desert environments. Many reptiles have highly efficient kidneys that help them thrive on little water, too. The kidneys remove most of the water from a meal before excreting waste, which is mostly uric acid.
Like all cold-blooded animals, reptiles are ectotherms, meaning they get their body heat from the environment. This allows them to use their behavior, such as basking in sunny places to warm up or finding shady spots or going underground to cool down, to regulate their temperature. They also consume a lot of insects and other prey that are ectotherms, which allows them to get some of their energy from the food they eat.
Highly Efficient Kidneys
Reptiles evolved from water-dwelling ancestors, and as the first vertebrates to live on land, they developed many adaptations that allow them to thrive in terrestrial habitats. Some are herbivores (eat only plants), some omnivores (eat both plant and animal material) and some are carnivores (eat meat).
Marine reptiles have evolved mechanisms for osmoregulation, maintaining the balance of water and salt in their bodies. They also have large lungs and can store oxygen in specialized tissues, enabling them to dive for extended periods of time. Marine iguanas, for example, can forage along the surface of rocky ocean waters and can dive deep to the ocean floor to search for algae. Their kidneys have been adapted to excrete waste solutes in an extremely efficient manner.
The kidneys of all reptiles are highly vascular, meaning that they have many blood vessels that bring in nutrients and eliminate wastes. But the kidneys of aquatic reptiles are more adapted for the water than those of terrestrial reptiles. They are equipped with glomerules, which are organelles that filter the blood and remove excess water and urea.
The kidneys of aquatic reptiles also have highly efficient membranes that regulate the balance of water and salt in their body fluids. They also have permeable skin to allow the body to absorb freshwater by osmosis. This enables them to forgo drinking water on dry land, as they can obtain all the water needed from their food and through cellular respiration.
As reptiles are ectotherms (animals whose body temperature depends on the environment rather than from metabolism) they have a limited number of ways to thermoregulate. For example, they can bask in sunlit places to warm up and find shady spots to cool down, or they can dig themselves into a cool burrow. Reptiles may also use their tail to generate heat. This behavior can also serve as a deterrent against predators, as snakes often perform defensive displays such as puffing up their bodies and hissing to scare off potential attackers.
Thermoregulation is a crucial factor in the success or failure of a reptile species to survive in its habitat. Reptiles that fail to attain a sufficiently high operative field body temperature run the risk of death. Thermoregulation has also been an important evolutionary driver in a number of adaptations which enable reptiles to survive in particular environments.
In aquatic reptiles (e.g. sea-snakes and marine tortoises) the environmental gradients which affect their body temperatures are much more restricted. This is because they must take short excursions out of the water to obtain food and they need to re-warm up rapidly when returning. Therefore they have developed a series of physiological adaptations which facilitate rapid heating and slow cooling.
Terrestrial reptiles, including burrowing forms and some neotropical rainforest species, have a wider range of environmental gradients to thermally regulate themselves. For example, the soil in these regions is comparatively hot close to the surface. In addition some reptiles, such as burrowing frogs or the tuatara of Brittany, utilise the body’s ability to absorb varying amounts of heat by moving around in their habitats.
Many species of lizards use caudal autotomy, the ability to shed and regenerate a tail portion, as an effective anti-predation tactic. This strategy has several benefits including increasing the odds of escape from a predator, decreasing the energy needed to maintain balance and locomotion, and the ability to stockpile resources (e.g., skin, muscles, blood) while the tail is regenerating. Despite these advantages, there are also disadvantages. First, the regenerated tail lacks the ability to perform most behavioural and ecological functions of the original tail. Additionally, regenerating a tail requires substantial amounts of energy that may leave the lizard vulnerable to predation.
Although other reptiles can shed their tails, only squamate reptiles do so consistently along pre-existing fracture planes. This behaviour may have evolved in captorhinid lizards because the smaller body size of these taxa led to higher predation risk.
To prevent this, the lizard stretches its head and neck in a threat display and releases its tail. The wriggling motion of the detached tail creates a deceptive sense of continued struggle and can distract the predator so it will miss the rest of the animal’s body. After a while, the cartilaginous rod that replaces the lost vertebrae is regenerated and the lizard’s original tail functions return. This is similar to the regenerative processes of the limbs of amphibians.