Several groups of reptiles that form important, if not dominant, elements of the fauna of the Eastern Hemisphere are largely or completely absent from the American tropics.
In river systems where the gradients are not steep, currents are slow, and quiet pools alternate with riffles, large numbers of characins, cyprinids, and suckers and other types of catfish are conspicuous elements of the fauna.
Gekkonid lizards of the genus Stenodactylus Fitzinger, 1826 [ 30] are one of the most characteristic and abundant elements of the fauna of the arid and hyper-arid regions of Arabia and North Africa [ 31].
It was a rare constituent of this fauna.
The megaherbivorous dinosaurs primarily represented by ankylosaurs, ceratopsids, and hadrosaurids form the most significant component of this fauna [ 4- 6], in terms of both population (75 82% of total dinosaur fauna; [ 7]) and body size.
Though Darwin was indeed interested in showing that extinction was not catastrophic but rather took different elements of a fauna at different times, the clear implication is that, while taxa such as the genus Megatherium became extinct, the fossil cavy species, now also extinct, has been replaced by a closely related, congeneric species.
Based on fossils of animal embryos, it is thought that elements of the Ediacaran fauna appeared as early as 590 to 600 million years ago.
Further, we investigate the biogeographic origins of this fauna by examining the relative contributions of southern, Beringian, and high-Arctic elements to Churchill species composition.
Thus, the presence of saxicolous habitat can reduce the time required for regrowth to attain a climax community structure and elements of old growth fauna.
