Earth Sciences 2266F/G Lecture Notes - Lecture 9: Branchial Arch, Fish Scale, Mangiafuoco
26 Jul 2016
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Document Summary
Within this type of fish: sharks, rays, dogfish. No body fossils found; people only find scales or teeth in ordovician-silurian. Earliest body fossil was found in the early devonian. Sharks are used to study the origin of jaws. Without swim bladders, it"s impossible for sharks to evolve lungs, thus sharks cannot have been the ones to evolve into land animals. Also lacks strong bony limbs needed to get onto land. They were suppressed hard to explain by darwinian theory. Only after the f-f mass extinction, sharks start to radiate. In modern sharks, their teeth is single bladed. But in the beginning of sharks, they had multicusped teeth. Today, not all sharks have this kind of single bladed teeth. E. g. if you go deeper, some sharks still have the multi-cusped teeth. These teeth are not very good for slicing flesh or meat simply good for grabbing since there are so many cusps; they can hold their prey.
