>Go back to the latest Precambrian. How many of the phyla found in the
>Cambrian are also found in the Percambrian?
As body fossils the following are accepted by nearly all workers: Sponges,
Coelenterates (probalby including all or most living classes), and
Mollusks. There is less agreement on fossils strongly resembling annelid
worms, echiurid worms, and echinoderms. This is in addition to the trace
fossil record which shows an increase in both the number and diversity of
burrows through time during the latest Precambrian. All workers that I
know accept these burrows as being made by organisms of at least annelid
grade. Given that nearly half of all living phyla are "worms," and that
worms have a miserable body fossil record, it is not unreasonable to assume
that several phyla are represented by these burrows.
Many of the fossils from the earliest Cmbrian have morphologies that are
intermediate between living phyla. A result consistent with expectation of
common descent. Some of these issues are addressed in an upcoming article
of mine in the Decemember issue of Perspectives.
Keith B. Miller
Department of Geology
Kansas State University
Manhattan, KS 66506