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Australia: The Land Where Time Began |
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Cambrian Explosion - Mollusca Nearly all small shelled molluscs from the Early
Cambrian are fragile, but they are well represented in small shelly
faunas appearing first in Stage 1. Similar to Gastropoda, these SSFs
have coiled shells, though the authors suggest they are not likely to be
crown forms, and small shells that have been assigned to Bivalvia that
may also represent stem groups. There are also groups that appear likely
to be molluscs or mollusc-related, that are entirely extinct:
Rostroconchia, a form resembling bivalves, though with a single shell;
various clades that are univalved among what was previously called
Monoplacophora; and possibly Probivalvia, that has 2 articulaed shells,
though doesn’t much resemble Bivalvia in gross shape. Hyolihida, which
is generally regarded as a separate extinct phylum that is close to
Mollusca, which have coiled shells the apertures of which are closed by
an operculum, a second flattish shell. The hyolithids, tending to be
measured in millimetres, are especially common among
SSFs, and are also
found in assemblages of other types, that lasted about 280 My, some
later forms reaching 40 cm in length.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |