Earth Sciences 1083F/G Lecture Notes - Lecture 20: Squamosal Bone, Skull, Keratin
12 Sep 2016
School
Department
Course
Professor
Document Summary
Gelatinous eggs of amphibians cannot survive out of water, so amphibians are limited in terms of the environments in which they can lay their eggs. Water is needed for the external fertilization that is characteristic of amphibians so, again, amphibians must return to some sort of water body to reproduce. Amphibians have gas-permeable skin to aid their inefficient lungs in breathing. This skin must be kept moist, so restricted to moist environments. Change in post-cranial skeletal structure (sprawling to upright) The appearance of the amniote egg was a great leap forward for tetrapods (four-legged, land-dwelling vertebrates) The amniote egg is certainly not immune to various dangers posed by terrestrial conditions: however, the amniote egg provided a greater range of lifestyles that did the eggs of fishes and amphibians. We can view the internal amniote egg as being analogous to a spacecraft: taking an environment will all things necessary for survival and making it self- contained.
