Reptiles first emerged during the Carboniferous period (about 359–299 million years ago), evolving from amphibian ancestors. This transition marked a significant shift from aquatic to terrestrial life, driven by the need to adapt to dry environments. The earliest reptiles were part of the Reptiliomorpha group, which included early amniotes—organisms that laid eggs with protective membranes, a key adaptation for land reproduction.
Diapsid and Synapsid Divergence
During the Permian period (about 299–252 million years ago), reptiles diversified into two main lineages: Diapsids and Synapsids. Diapsids, characterized by two temporal fenestrae in their skulls, led to the evolution of dinosaurs, birds, and modern reptiles. Synapsids, with one temporal fenestra, gave rise to mammals. This period of diversification was marked by the Permian-Triassic extinction event, which wiped out many species but allowed reptiles to dominate terrestrial ecosystems afterward.
Adaptations for Terrestrial Life
Reptiles developed several key adaptations that enabled them to thrive in terrestrial environments. These include scaly skin made of keratin to prevent water loss, amniotic eggs that provide a protective environment for embryos, and advanced lung systems for efficient respiration. The development of ectothermy in most reptiles allowed them to regulate body temperature through external sources, reducing their metabolic energy needs compared to endothermic organisms.
Major Groups of Reptiles
Reptiles are divided into several major groups, each with unique evolutionary paths. These include:
- Lepidosaurs: This group comprises lizards, snakes, and tuataras, all sharing a common ancestor with distinct diapsid skulls.
- Archosaurs: This lineage includes crocodiles, birds, and dinosaurs, characterized by advanced social and parental behaviors.
- Testudinomorphs: Turtles and tortoises, with their unique shell structures, have a more distant common ancestor with diapsid reptiles but are distinct in their evolutionary path.