There are more than 10,000 species of reptiles and among these are animals that are known to live mostly on land or in the water. It may make you wonder to what extent reptiles are aquatic animals and how long your pet iguana or terrapin could live underwater for.
Some reptiles are aquatic but most species are terrestrial. Reptile species live in a wide range of habitats from woodlands and bog marshes to grasslands and deserts and only a few species have adapted to life in a marine environment, either partly or fully.
It’s easy to assume that crocodiles, alligators, and sea turtles have always spent their lives underwater, but this is a secondary adaptation they have developed since the majority still return to land to nest. Let’s look at which reptiles are fully aquatic, how long most reptiles can breathe underwater, and more.
What is Aquatic Living?
The term ‘aquatic living’ essentially means living or growing in water, so this refers to any organism – plant or animal – that resides in rivers, lakes, oceans, ponds, or seas. Narrow this definition down further and aquatic life can refer to life spent partly in water, which describes only a small handful of reptiles.
And an aquatic reptilian habitat may be in marine (sea water), freshwater (ponds, marshes, and lakes etc) or brackish water (somewhere between the two, where rivers or streams meet the ocean).
Are Reptiles Terrestrial or Aquatic?
Some reptiles are semi-aquatic but the vast majority are terrestrial. Almost 60% of all reptiles are lizards and 99% of all lizard species are fully terrestrial, giving you some indication of how rare a fully aquatic animal is among the reptile group.
This mix of water and land-dwelling reptiles is due to the fact that around 260 million years ago, reptiles began evolving from fully aquatic amphibians and developed limbs, allowing them to walk on land, which gave rise to the dinosaurs.
By the Jurassic period (roughly 200-145 million years ago), the modern reptiles began to appear with only a small number of reptiles re-entering the ocean such as sea snakes and sea turtles. But once the remaining reptile groups (crocodiles, lizards, snakes) developed the adaptations to living on land, they no longer had a reason or the skills to live out in the open sea waters.
Unlike fish and amphibians, some reptiles inhabit the water at some stage in their life cycle – such as to breed or hunt – but they do not reside in the water permanently. This is why only sea turtles make a brief appearance on land when they come to lay their eggs before returning to the environment they’re best adapted to since the dinosaur age – the ocean.
What Reptiles are Fully Aquatic?
Though there are four main reptiles that live primarily in the sea (which we’ll discuss below), no reptile exists that is fully aquatic. Sea turtles and Sea snakes are almost fully aquatic but even they must return to the surface every few hours to breathe.
It can be argued that sea snakes are the closest creature to a fully aquatic reptile because some true species of sea snake breathe underwater for up to 8 hours and even give live birth underwater.
Truly fully aquatic reptiles have not existed since the marine reptiles of the Mesozoic era (around 250 million years ago) including Ichthyosaurs, Plesiosaurs, and Mosasaurs – all of whom adapted so well to living in water that they became incapable of returning to land.
Do Reptiles Live in Water?
All reptiles have lungs and are technically air-breathing animals so they cannot live indefinitely in water. However, there are marine reptiles that live the majority of their lives in the sea such as the Sea turtle, Saltwater crocodile, Sea snake, and the Marine iguana.
As well as possessing lungs, reptiles are also ectothermic (cold-blooded) and cannot permanently sustain their core body temperature, so living in cold waters would not allow many reptiles to live comfortably as they would not be able to stay warm enough to survive. With their large bodies, Sea turtles are the exception, however, as they carry enough extra insulation to slow down the cooling effect when they enter colder waters.
Saltwater crocodiles, Marine iguanas, and Sea snakes each occupy the water and ‘live’ in it in the sense that they spend their days hunting, catching, and eating their prey, but most reptiles will do their breeding and laying of eggs/producing offspring on land.
Can Reptiles Swim?
Sea turtles and crocodiles are extremely well adapted to swimming due to their respective broad fins and webbed claws which make gliding through the water a breeze.
The only skilled ocean-swimming lizard species on the planet is the Marine iguana, living exclusively on the Galápagos Islands. These iguanas are herbivores and prefer to eat underwater algae, so they routinely swim beneath the surface using their long, flattened crocodile-like tails and cling on to the rocks beneath in heavy currents while they feed on the seaweed below.
Can Reptiles Breathe Underwater?
No, by and large, reptiles cannot breathe underwater as they have lungs, not gills like amphibians and must come up to the surface for air every hour or so. There are quite a few reptiles that can hold their breath for long periods, though. Terrapins can hold it for 30 minutes, while larger turtles can hold their breath for up to an hour or more.
A fascinating scientific discovery in 2021, however, found that the semi-aquatic Anole lizard in the Caribbean and Latin America is actually capable of breathing or ‘re-breathing’ underwater for up to 18 minutes without returning to the surface!
Anoles do this by exhaling underwater, causing a large oxygen-filled water bubble to form on their nostril, which they then continue breathing or re-breathing through for several minutes. Find out more about these amazing creatures here.