|
When we first discovered
this unique site over a decade ago in northern Arizona, our main
concern was the collection of the rare Zacanthoides trilobites
present and the associated hyolithids. Mixed in with the countless
arthropod molts were the scattered remains of another organism,
which appeared to the naked eye as a small net-like sponge. At
that time, we speculated on what they could be, but nothing further
came of their presence for a few years. The last time we visited
this site, we discovered that the "sponges" were located
in a layer about six inches below the trilobite beds and often
did not contain a single other type of fossil. An increased effort
was made at that time to collect new material, and take a closer
look when we returned.
Since then, the
material has been re examined under the microscope and serial
sections were made, and it soon became evident that this was
certainly not a sponge! We found that these fragments were that
of some sort of colonial animal, perhaps an early cnidarian or
hydrozoan of some sort that was reminiscent of the later Paleozoic
Favosites Tabulate Coral. At this point, we had never even heard
of the term "Coralomorph", and after a new program
to re-photograph the fauna from this site was undertaken this
year, I posted some diagnostic images on the "Fossil Forum"
(thefossilforum.com) to see if anyone had collected Cambrian
material similar to these animals shaped like bundles of tiny
hexagonal tubes. One of the members (Piranha), whose key interests
in Cambrian trilobites recognized what we had found was a primitive
coral, and pointed us to a paper by Melissa Hicks, University
of Nevada in 2006. Photographs in the paper revealed an anthozoan
nearly identical to what we have been finding. The coralomorph
Harklessia yuenglingensis which at this point had only been found
in our part of the country in one locality in nearby Nevada.
The paper lists coralomorph localities in world wide locations,
and of the dozen or so listed - this was the only one in the
USA.
Continued review
of additional research papers on the subject revealed that while
the very first primitive tabulate coral like cnidarians existed
in the early Cambrian (Tomotian), The fossil record of corals
is nearly non existent for Middle Cambrian to Early Ordovician.
After that, Tabulate and Rugose corals exploded in diversity
and were major dominant reef builders during the Paleozoic. During
the transition from the earlier corals to first tabulates, a
peculiar coral like animal evolved called the "coralomorphs"
with still uncertain affinities to later Paleozoic true corals.
What we had found at this remarkable lower middle Cambrian site
was one of the enigmatic colonial hydrozoans that were part of
this transition.
Our conclusions
are that while the microscopic details of our coralomorph are
not a perfect match to the not so clear images in the paper,
it more than likely is either Harklessia sp., or a very similar
primitive cnidarian. Also, we have not yet found any reports
of coralomorphs for Arizona's Cambrian rocks and this may be
a significant extension of the range of a Harklessia type coralomorph.
This was surprising, since such extensive work on the fauna of
the Cambrian strata in the Grand Canyon was done last century.
|
