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Australia: The Land Where Time Began |
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Cambrian Explosion In this section the authors1 review the
morphologies of the major groups that appear as fossils during the
Cambrian Explosion, and concentrate on features that suggest an affinity
with extant groups. Architectural grades do not appear in a regular
sequence of complexity over time, instead body plans ranging across
levels of complexity, from sponges to chordates, appear geologically
abruptly. These organisms must have had a rich history of divergence and
expansion for which there are few if any known records, though their
appearance is the earliest known in the fossil record in most of these
groups. The fauna of the explosion reflects the exploration of many
adaptive pathways in the marine biosphere that was evolving. Marine
ecosystems with characteristics that can be recognised in the oceans of
the present, a legacy that extends back about 500 My, as the burgeoning
fauna interacted with physical and biotic aspects of the environment. Basal
Metazoan Clades
Within the metazoan tree a suite of sponges and
sponge-like organisms have been found to be at the base of the tree, and
are important species in the Cambrian Faunas. There are a variety of
problematic groups, as occurs in many other groups, the phylogenetic
affinities for which are still unclear.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |