Terrestrial adaptations necessitated the production of

Terrestrial animals face the challenge of conserving water due to its limited availability. Therefore, they have evolved adaptations to convert toxic ammonia into less toxic compounds like urea (in mammals and some amphibians) or uric acid (in birds, reptiles and insects), which require less water for excretion. This conversion allows for more efficient waste excretion with reduced water loss, making it suitable for survival in dry terrestrial environments, where water conservation is critical. 

Ammonia is the most toxic waste. Urea is moderately toxic and uric acid is the least toxic among the three. Ammonia is excreted by most aquatic animals (not terrestrial animals).