Trilobites are not the oldest metazoans in most places around the world.
Precambrian metazoans are known from Siberia, China, England, Canada, the
U. S., Australia, southern Africa, northern Africa, and probably several
other places. Nobody knows what many of them are, but some of the small
shelly fossils may be derived from armored lobopods. However, our
knowledge of the Precambrian and basal Cambrian faunas is still very
preliminary, and any claims about the time of first appearance of any
phylum are probably premature. For metazoans, the data are not really
adequate to suport or refute any claims about the relative time of
appearance.
David C.