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The Ancient Eye

Trilobytes are among the oldest of the metazoans (multicellular animals with differential tissues and organs.) They were incredible complex, especially for being the earliest with a brain, nervous system, digestive tract , muscular system, and a compound eye. The puzzle of their complexity was emphasized by the lack of evolutionary predecessors. Trilobytes were strictly marine animals that first occurred at the base of the Cambrian. It was thought they were among the first fossils since no undisputed form was known in the Precambrian. There are a wide variety of fossils of simple plants and animals among the late Precambrian rocks, but nothing as complex as the trilobyte. When soft-bodied trilobytes were discovered in the late Vendian (late Precambrian) period, it corroborated the trilobyte tracks that had been discovered and it is probable that the trilobyte’s predecessors were often not fossilized because of their lack of hard parts.

Hard shells were primarily a Cambrian development. The evidence is that non-shelled trilobytes lived in the Precambrian and developed hard shells of elegant and beautifully simple structures in the Cambrian. They are the most abundant ad dominant fossils from the Cambrian, after which growing competition caused them to develop increasingly specialized and bizarre forms with complex spines , antlers and other armor probably meant for defense.

The trilobyte’s inevitable decline was prolonged during the Carboniferous period, their antlers and spines disappearing, the specialization preventing them from adapting. Declining in numbers and in function, plain, small and defensive, the entire class of animals in the largest phylum on earth, the arthropods, became extinct by the end of the Permian. They had wandered the earth for 300 million years, and had developed 1,500 genera and over 10,000 species. They disappeared by the end of the Permian.

(edited from Larry Solomon in Fossil News, via the Petrograph, via the Agatizer 7/06, via Rock Rollers 10/06, viaDelvings 12/06)