I have no academic background in paleontology so I found this simple fact fascinating:
Trilobite populations were once thought to have composed the majority of aquatic life during the Cambrian, due to the fact that their calcium carbonate-rich shells were more easily preserved than those of other species which had purely chitinous shells.
---- Ward, Peter (2006). Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere
Considering the fact that chitin is a polysaccharide, a long-chain polymer derived from glucose, I can certainly understand why it would break-down more easily than a calcium carbonate shell.
I realize that this is no doubt a yawn-inducing post for many PS participants—but for this has-been linguist, it sure helps explain the “Cambrian explosion.” If someone produced “fast fact flashcards” for paleontology basics, this kind of concise explanation would be a big help for amateurs like me.