Not anymore. There is a usually pre-trilobite basal Cambrian fauna of
"small shelly fossils" and a late Precambrian fauna including some "small
shelly fossils", Ediacaran-type organisms, and the like. I do not know
what exact age the rumored Precambrian trilobites were supposed to be. If
they do prove to be really from the Precambrian, it would push the origin
of trilobites back again, but right now there are a lot of earlier
metazoans than trilobites.
> Thus you are assuming "descendants" and "transitional", and then
>using this assumption to justify your assumption that the evolutionary
>history of the trilobites (or "arthropods") involves the lobopods, which
>appear after the first arthropods. Does this strike you as a bit
>tautological?
A bit, but not entirely. Intermediate forms clearly do exist.
Intermediate forms may reflect transition, convergence, or creation of
intermediate forms. Many intermediate forms fit exactly how they would be
expected to if they are transitional forms. Thus, it is not unreasonable
to suppose that intermediate forms for which additional data are lacking
may also be transitional.
David C.