Reptiles are a diverse group of vertebrates distinguished by their ectothermic metabolism, meaning their body temperature is regulated by external sources. They typically possess dry, scaly skin and often reproduce by laying eggs, though some species give birth to live young. This broad classification includes around 12,000 living species, encompassing four main orders: Testudines (turtles), Crocodilia (crocodiles and alligators), Rhynchocephalia (tuataras), and Squamata (lizards and snakes). These creatures inhabit a vast array of environments across the globe, excluding only Antarctica, showcasing a wide range of forms and behaviors.
Measuring Reptile Dominance
Determining the “most common” reptile is complex, as commonality can be measured through various metrics. These metrics include total population size, which refers to the sheer number of individuals of a species, and geographic distribution, indicating how widely spread a species or group is across different regions. Another measure is biomass, which represents the total weight of all individuals within a group. While some animal groups, like plants and bacteria, have immense biomass, that of reptiles and amphibians is negligible. Therefore, identifying the most common reptile often prioritizes population numbers and widespread distribution over total mass.
The Reigning Reptiles
When considering population size and widespread distribution, the Order Squamata, which includes lizards and snakes, stands out as the most dominant reptile group. Lizards alone account for over 7,000 species, representing approximately 63% of all known squamates. These adaptable creatures are found on every continent except Antarctica, thriving in a broad spectrum of habitats. The viviparous lizard exemplifies this widespread success, living farther north than any other non-marine reptile and possessing the largest range of any terrestrial lizard, extending into subarctic regions.
Keys to Their Success
Several biological and ecological factors contribute to the widespread abundance of lizards. Their ectothermic nature allows for a highly efficient metabolism, enabling them to endure long periods without food. Furthermore, their waterproof skin, fortified by keratin and waxy lipids, significantly reduces water loss, an adaptation that supports their survival in arid environments.
Reproductive strategies, such as the evolution of the amniotic egg with its hard shell, provided independence from water bodies for reproduction, reducing predation pressure on their offspring. Some species, like the viviparous lizard, also give birth to live young, a trait beneficial for thriving in colder climates.
Lizards also demonstrate remarkable dietary flexibility, with varied jaw shapes allowing them to consume diverse prey, from insects to larger mammals. Their ability to utilize a wide range of habitats, from deserts to forests and even urban areas, further underscores their adaptive capacity.
Other Highly Abundant Reptiles
While lizards represent a significant portion of the most common reptiles, other groups also demonstrate considerable abundance. Snakes, also members of the Order Squamata, are globally widespread and numerous. Various species, such as garter snakes, contribute substantially to reptile populations across their extensive ranges. Beyond the Squamata, other prominent reptile groups include turtles and crocodilians. Though generally less numerous than lizards and snakes, these groups maintain significant populations in their respective ecological niches.