Reptiles are a diverse group of animals that share certain key characteristics, such as scaly skin, ectothermic metabolism, and egg-laying reproductive systems (with some exceptions). They are classified into several orders, each representing a distinct evolutionary lineage with unique adaptations. The main orders of reptiles are Squamata, Crocodylia, Testudines, and Rhynchocephalia.
Squamata
The order Squamata includes lizards, snakes, and amphisbaenians. This is the largest order of reptiles and is characterized by the presence of keratinized scales, flexible jaws, and a unique parthenogenetic reproductive system in some species. Squamates are highly adaptable and can be found in a wide range of habitats, from deserts to aquatic environments.
Crocodylia
Crocodylia includes crocodiles, alligators, caimans, and gharials. Members of this order are known for their semi-aquatic lifestyles and strong parental care. They possess synapomorphic features like a four-chambered heart and are more closely related to birds than to other reptiles, sharing a common ancestor that emphasizes their evolutionary significance.
Testudines
The order Testudines comprises turtles and tortoises, known for their distinctive bony or cartilaginous shells that provide protection. Testudines are ancient reptiles with a history dating back to the time of the dinosaurs. They are characterized by their slow metabolism and long lifespans. Unlike other reptiles, they have no external temporal fenestrae in their skulls, which is a key feature of their unique evolutionary path.
Rhynchocephalia
Rhynchocephalia is a lesser-known order represented by the tuatara, which is native to New Zealand. Rhynchocephalians resemble lizards but are genetically distinct, possessing a unique parietal eye and ancient characteristics that link them to early reptiles. They thrive in cooler climates and have retained many primitive traits, making them vital for understanding reptile evolution.