Maotianshan and Burgess Shales are two of the few rocks which had a near perfect media for fossil formation. Unfortunately other periods of time are not so blessed. The Maotianshan Shales have recently yielded up a relative of the Trilobite which did not have a hard exoskeleton. This fits in with a pre-Burgess Shale history to creatures that seemed to have sprung fully formed. Rapid evolution of many phyla to take advantage of a favorable environment and “feed on” other plants and creatures still took some 20 to 80 million years. Yes it’s a geological blink of the eye.
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