Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic, why?
Terrestrial adaptation requires the production of less toxic nitrogenous wastes like urea and uric acid for the conservation of water. Aquatic animals excrete ammonia which requires large amount of water to dissolve. The huge quantity of water is easily available to such animals from surroundings.
However, for terrestrial animals, such a huge quantity of water is not available, hence, they modify $NH_3$ to comparatively less toxic products like urea and uric acid which require less amount of water for their excretion.