cambrian period

English Thesaurus

1. from 544 million to about 500 million years ago; marine invertebrates (noun.time)

instance hypernym	:	geological period, period,
definition	:	a unit of geological time during which a system of rocks formed (noun.time)

part meronym	:	paleozoic, paleozoic era,
definition	:	from 544 million to about 230 million years ago (noun.time)