Trilobites lived during the Paleozoic era 570 to 250 million years ago and were most prevalent in the early part of that era. The trilobites were named for the arrangement of their exoskeleton, or outer shell, into three lobes. They usually show a superficial five-part symmetry, and generally are equipped with peculiar tube feet. The phylum name is derived from spinney skin. Conodont, form of limestone, commonly found in marine limestones dating from the Cambrian Period to the Triassic Period, from about 570 million to about 210 million years ago.
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