Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic, why?
Terrestrial animals are generally ureotelic or uricotelic because ammonia is the most toxic form of nitrogenous waste and requires a large amount of water for its elimination. Since terrestrial animals have limited access to water, excreting ammonia would lead to excessive water loss from the body.
Terrestrial adaptation necessitated the production of lesser toxic nitrogenous wastes like urea and uric acid for conservation of water. Urea and uric acid are less toxic and can be excreted with minimum loss of water. For instance, uric acid is excreted as pellet or paste with minimal water loss, making it suitable for reptiles, birds, and insects.
Explanation
The textbook clearly explains that ammonia requires large amounts of water for elimination due to its high toxicity and solubility. Aquatic animals can afford to be ammonotelic because they have constant access to water for diffusion across body surfaces. However, terrestrial animals evolved to convert ammonia into less toxic forms (urea or uric acid) to conserve water, which is essential for survival on land.