Geology Reference
In-Depth Information
The question that paleontologists are still debating
is how many phyla arose during the Cambrian, and at the
center of that debate are the Burgess Shale fossils. For years,
most paleontologists placed the bulk of the Burgess Shale or-
ganisms into existing phyla, with only a few assigned to phyla
that are now extinct. Thus, the phyla of the Cambrian world
were viewed as being essentially the same in number as the
phyla of the present-day world, but with fewer species in each
phylum. According to this view, the history of life has been
simply a gradual increase in the diversity of species within
each phylum through time. The number of basic body plans
has therefore remained more or less constant since the initial
radiation of multicelled organisms.
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Figure 21.5
Archaeocyathids Restoration of a Cambrian
reef-like structure built by archaeocyathids.
Images not available due to copyright restrictions
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