terrestrialisation

Terrestrialisation is a geological and evolutionary process where aquatic organisms adapt to life on land. This transition involves significant physiological, anatomical, and behavioral changes to overcome the challenges of a terrestrial environment, such as desiccation, gravity, and respiration.

The process typically begins with organisms that spend part of their lives in water and part on land, often referred to as semi-aquatic. Over evolutionary time, adaptations accumulate that allow for increasingly greater independence from water. Key evolutionary steps include the development of limbs for locomotion, lungs for breathing air, and protective outer coverings like skin or shells to prevent water loss. Reproduction also undergoes changes, with the evolution of internal fertilization and amniotic eggs in many terrestrial vertebrates, which frees them from the need to lay eggs in water.

Terrestrialisation is not a single event but a gradual process that has occurred multiple times throughout Earth's history. It is exemplified by the transition of fish ancestors to tetrapods, which led to the diversification of amphibians, reptiles, birds, and mammals. Similarly, arthropods, such as insects and arachnids, also underwent terrestrialisation from aquatic ancestors, becoming a dominant form of life on land. The study of terrestrialisation provides insights into evolutionary adaptation and the colonization of new environments.