Tetrapods: Out on a limb

Reptiles have thrived on Earth for over 300 million years. As a class of vertebrates (Reptilia), they are characterised by their dry, scaly skin and their ability to inhabit nearly every continent.

What Makes a Reptile a Reptile?

• Ectothermic Nature: Often called "cold-blooded," reptiles rely on external heat sources, like the sun, to regulate their body temperature.

• Scaly Skin: Their bodies are covered in scales or scutes made of keratin, which prevent water loss and provide protection.

• Amniotic Eggs: Most reptiles lay eggs with protective membranes that allow embryos to develop on land without drying out—a major evolutionary milestone.

• Lung Respiration: All reptiles breathe air using lungs.

• Four Limbs: Reptiles are defined as having four limbs or being descended from four-limbed ancestors (such as snakes).

A Journey Through Reptilian Diversity

The modern world of reptiles is comprised of four primary living orders:

Order Common Name Key Traits

Squamata Lizards and Snakes The largest order (10,000+ species); includes varied lizards and limbless snakes.

Testudines Turtles and Tortoises Ancient reptiles distinguished by a protective bony shell.

Crocodylia Crocodiles and Alligators Large semi-aquatic predators with powerful jaws and an ancient lineage.

Rhynchocephalia Tuataras "Living fossils" found only in New Zealand; the last survivors of an ancient group.

Local Spotlight: Reptiles of the Sid Valley

While Britain has six native reptile species, the Sid Valley and its surrounding heathlands provide a critical home for four of them. These species rely on the sandy soils of local heathlands for basking.

Meet the Locals:

• Adder (Vipera berus): Britain's only venomous snake, identifiable by a zig-zag pattern on its back. They often hibernate in groups called hibernacula.

• Grass Snake (Natrix natrix): A non-venomous snake often found near water, where it hunts frogs and newts.

• Common Lizard (Lacerta vivipara): Frequently seen basking on warm, south-facing pathways before scurrying into the undergrowth.

• Slow Worm (Anguis fragilis): Despite appearances, this is a legless lizard, not a snake. They are common in gardens and compost heaps.

Crucial Ecological Roles

Reptiles are far more than just "scary" or "slithering" creatures; they are essential to a balanced environment:

• Predators: They regulate prey populations, ensuring no single species becomes dominant.

• Prey: They serve as a critical food source for other animals in the food web.

• Ecosystem Engineers: Some species, like crocodiles and turtles, modify their habitats in ways that benefit other wildlife.

Threats and Conservation

Despite their resilience, reptiles face unprecedented challenges from human activities.

• Habitat Loss: Urbanisation and agricultural expansion destroy and fragment vital habitats.

• Climate Change: Altered temperatures disrupt reptile behaviour, reproduction, and distribution.

• Other Threats: Pollution, invasive species, and the illegal pet trade further deplete populations.

Why Conservation Matters: Protecting reptiles preserves millions of years of evolutionary history and maintains the biological heritage of our planet.