Thus, according to Walcott, ancestral precursors to the trilobites and other distinctive Cambrian forms had existed, but they were not fossilized in sediments that would later be elevated above sea level until early in the Cambrian; instead, before the Cambrian, during a period when sea levels were lower, trilobites and their ancestral forms were being deposited offshore in what are now only deep-sea sediments.24 Walcott named this cryptic period of time in which trilobites and other animals were rapidly evolving offshore as the “Lipalian interval.” (The term “Lipalian” is derived from the
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