Reptiles are a diverse group of vertebrates that first appeared over 300 million years ago, adapting to a wide range of environments from deserts to rainforests. They are characterized by their scaly skin, which provides protection and helps prevent water loss, and by their ability to lay amniotic eggs, which can develop on land. The major groups of reptiles include Crocodylia (crocodiles and alligators), Squamata (lizards and snakes), Testudines (turtles and tortoises), and the extinct Sphenodontia (tuataras).
Reptiles are ectothermic, relying on external heat sources to regulate their body temperature.
Their amniotic eggs contain membranes that support development outside water, a key adaptation for terrestrial life.
The four main reptile groups—Crocodylia, Squamata, Testudines, and Sphenodontia—show a wide range of forms and habitats.
Amphibia is not a reptile group; the main reptile groups are Crocodylia, Squamata, Testudines, and Sphenodontia.
Crocodylia includes crocodiles, alligators, caimans, and gavials. These large, aquatic reptiles have powerful jaws, a four-chambered heart, and parental care for their young, traits that show advanced evolution among reptiles. They are mostly found in tropical regions and are excellent swimmers thanks to their streamlined bodies and webbed feet.
Crocodylia are the closest living relatives of birds among reptiles.
They possess a four-chambered heart, improving circulation efficiency.
Strong parental care is uncommon among reptiles but is seen in crocodylians.
Crocodylia have a four-chambered heart, unlike most other reptiles.
Squamata is the largest order of reptiles, encompassing lizards, snakes, and amphisbaenians (worm lizards). They are characterized by their scaly skin, which is regularly shed, and by highly movable jaws that allow them to consume large prey. Snakes, a sub-group within Squamata, have lost their limbs and possess unique sensory adaptations like heat-sensing pits.
Squamata includes both limbed (lizards) and limbless (snakes) forms.
They have kinetic skulls, enabling wide jaw movement.
This group exhibits diverse reproductive strategies, including egg-laying and live birth.
Squamata includes lizards and snakes, but not turtles or crocodiles.
Testudines, the turtles and tortoises, are easily recognized by their bony or cartilaginous shell, which provides exceptional protection. They have a slow metabolism and can live in a variety of habitats, from terrestrial to fully aquatic. Unlike other reptiles, their ribs are fused to the shell, limiting their ability to breathe rapidly.
The shell is a unique evolutionary adaptation for defense.
Testudines lack teeth; instead, they have strong, beak-like jaws.
They show remarkable longevity, with some species living over 100 years.
Testudines have ribs fused to their shell, a unique feature among reptiles.
Sphenodontia is an ancient group represented today by only two species of tuatara found in New Zealand. They resemble lizards but have distinct features like a well-developed parietal eye (third eye) and unique jaw mechanics. Tuataras have remained relatively unchanged for millions of years, making them living fossils.
Tuataras have a third eye on top of their head, used for regulating circadian rhythms.
Their teeth are fused to the jawbone, unlike those of lizards.
They can live over 100 years and have very slow metabolism.
Modern Sphenodontia (tuataras) are found only in New Zealand.
Reptile diversity spans remarkable adaptations across their major groups, from the protective shells of Testudines to the advanced cardiovascular systems of Crocodylia.
Major groups include Crocodylia, Squamata, Testudines, and Sphenodontia.
Key adaptations include scaly skin, amniotic eggs, and specialized jaws.
Reptiles occupy diverse habitats and exhibit a wide range of physiological and reproductive strategies.
All reptiles have amniotic eggs and scaly skin.
Crocodylia are the closest living relatives of birds among reptiles.
