The evolution of the terrestrial vertebrates: environmental and physiological considerations.

摘要: Physiological evidence has long been used to suggest that the gnathostomous vertebrates (those possessing jaws) were primitively fresh water. The same was also case for Osteichthyes (bony fish) and Tetrapoda (Amphibia, Reptilia, Aves, Mammalia). However, geological favours a marine origin as whole, and, gnathostomes osteichthyans in particular. Some of earliest amphibian remains may be associated with tidally influenced sediments. Furthermore, during early part Devonian, water chemistry well have different from today, lessening divide between non-marine environments. Urea formation via ornithine cycle, urea retention body fluids, are useful adaptations terrestrial life. They prevent excessive loss elimination nitrogenous waste. These abilities primitive gnathostomes, developed environment reduce osmotic dehydration. In aqueous medium, gaseous exchange is effected by gills. organs are, on useless air. For vertebrates, air-breathing an inflatable sac, moist linings, internal location. form sac osteichthyans, gnathostomes. Again, this adaptation life response conditions experienced marine, aquatic environment. A new model tetrapod evolution proposed light basic character ancestors tetrapods.