Basic Biology of Reptiles & Amphibians

Reptiles and amphibians are such familiar sights that sometimes we forget how different some aspects of their biology are from more “conventional” pets such as cats, dogs and rabbits.

Although they are vertebrates, like ourselves, and many of their bodily organs and functions are almost indistinguishable from our own, in other ways they are quite unlike us.

Of course, this accounts for some of the attraction for many reptile and amphibian keepers, and helps explain why an understanding of the quirks of their biology can lead to success when it comes to caring for these animals as pets.

Cold-Blooded

Read a few books on the subject and sooner or later you will come across the description of reptiles and amphibians as “cold-blooded.” It is an unfortunate term, not least because it is rather inaccurate. A wall lizard scurrying across the courtyard has a blood temperature very similar to our own; the difference is that while your body heat has been generated by your breakfast, his has been generated by basking.

Unlike mammals and birds, reptiles and amphibians cannot regulate their body temperature independently of their environment, making them what biologists describe as poikilothermic. This simple accident of biology explains why most of the world’s species of reptiles and amphibians are confined to the tropics and sub-tropical regions of the globe as well as why reptiles in captivity need hot-spots and thermal gradients in their tanks.

Breathing

Although amphibians are also poikilothermic, they don’t share the basking trick used by snakes and lizards to heat themselves up – and the reason is to do with the way they breathe. Reptiles have perfectly functional lungs, getting all the oxygen they need from breathing in the same way that we do. By contrast, although all but a few kinds of amphibians have lungs, they are, by comparison small and poorly developed and their arrangement of ribs and breastbone does not allow them to be used as efficiently as they are in reptiles.

Their solution is to breathe partially with lungs and partially through their skins, the oxygen diffusing across the thin, moist skin and entering their bloodstream. This inevitably means that, unlike scaly skinned reptiles, amphibians cannot sit out in strong sunlight or they would dry out and die. As a result, amphibians tend to be secretive and hide themselves away in shady spots during the day.

Reproduction

Nowhere do reptiles and amphibians differ from mammals – and from each other – quite so dramatically than when it comes to reproduction. Although some species have developed quite remarkable reproductive strategies, amphibians as a group have remained heavily tied to the water for breeding purposes, most going through the familiar egg-tadpole-frog sequence so familiar from our own garden ponds.

The details vary in terms of the tadpoles’ development, the method of mating and the duration of tadpole-hood, but the core of the story is unchanged. Even the most extraordinary approaches, such as Darwin’s frogs (Rhinoderma darwinii) which brood their young in their mouths and the Surinam toad (Pipa pipa) which implants eggs in its back until they hatch, are essentially simply variations on the same theme.

By contrast, back in prehistory, reptiles mastered the transition to the land with the combination of their scaly, water-tight skins and the invention of an enclosed egg – not in a shell as hard as a bird’s but in a leathery parchment, which does the job every bit as well.

In most species these eggs are laid and left to hatch in due course; unlike a bird, there is little parental care in most reptiles – the notable exception being alligators and crocodiles, which show remarkable dedication to their young. However, in some kinds of snakes and lizards, the eggs are retained inside the female, being laid simultaneously as they hatch, the young to all intents and purposes arriving into the world in much the same manner as any mammal. Three of Britain’s own reptiles reproduce in this way – the Common Lizard (Lacerta vivipara), the Slow Worm (Anguis fragilis) and the Adder (Vipera berus) – a breeding adaptation known as ovi-viviparity.

The biology of reptiles and amphibians is a fascinating study and contains so many remarkable aspects, including the likes of a snake’s ability to taste the air with its forked tongue, the way salamanders can re-grow lost limbs and how lizards shed their tails to escape predators. For anyone interested in keeping these remarkable creatures, delving into their extraordinary way of life and their unique adaptations to their environment and lifestyle makes a compelling – and thoroughly rewarding – pastime.

One thing is for certain, there’s no better way to succeed with the pets you keep than by finding out as much as you can about them.