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Modern sponges such as
this barrel sponge in the back of this image do not build reef structures. However, chaetetids,
sponge-like organisms found in the Pennsylvanian, did build
reef-like structures. At that time, reef-building scleractinian corals that are part of modern reefs
did not yet exist. |
New specimens are
constantly being added to the collection. These are referred
to as 'accessions'.
This page tracks the collection of a chaetetid specimen. |
Taxon: Chaetetes sp.
Age: Pennsylvanian
Horizon: Marble Falls Limestone
Location: Texas |
Here is a similar specimen as it looked in the field.
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At this site, chaetetid mounds
are exposed in the bed of a creek. The location of the specimens are carefully mapped.
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To get an idea of the size of this chaetetid mound, look for
the blue handle of a geologist's hammer near the bottom of the
image. From head to handle, this hammer is about a foot
long.
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The rock surface on the left
shows a mass of chaetetid heads in cross-section. The
upper parts have been eroded away. The partial specimen to the
right is much larger. |
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The living
animal's skeleton was made of calcite, but parts of it were
altered to silica by fluids flowing through the tiny pore
spaces after the animal died and was buried. We
discovered that alteration using a simple hand lens and dilute HCl.
*Note: Chaetetids have been placed in several groups, some regard them as tabulate corals, but we are following the placement within the phylum Porifera, class, Demospongea. |
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