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Australia: The Land Where Time Began |
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Cambrian Explosion - Chancellorida The Chancelloriids are a clade from the
Cambrian
that is now extinct that are believed to have had a feeding system that
was sponge-like, that were sessile, bag-shaped or vase-shaped forms with
bodies that were hollow and had no organs. Their body wall exteriors
were covered with hollow, aragonitic sclerites from which spine-like
rays radiated and that were attached to stalks on the surface of the
body (Randell et al., 2005).
It is believed these sclerites were probably for protection from
predators. It is common to find Chancelloriid sclerites in small shelly
faunas, and they are often found in archaeocyathan reefs. It has been
interpreted that they branched from organisms of sponge grade
(Butterfield & Nicholas, 1996), possibly being part of a radiation of
sessile benthic forms that used flagella to pump minute plankton for
feeding (Sperling, Peterson & Pisana, 2009). Early bilaterians such as
Halkieria are known to
have had hollow sclerites with basal foramina, however (see
Lophotrochozoa below) and such sclerites have been interpreted as a
synapomorphy of a distinctive clade, Coeloscleritophora (Porter, 2008).
A phylogenetic link between Chancelloriids and bilaterians is suggested
by similarities of the skeletal microstructures of the 2 clades (Porter,
2008). It has been argued that both Chancelloriids and bilaterians share
these characters, and it is possible they may even be eumetazoan
plesiomorphies, therefore the Coeloscleritophorans might represent the
lineage that links the early nonbilaterians to bilaterians, though
alternatively the characters may have been convergent.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |