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Arizona Chris

Tiny Bryozoans from the Permian Fort Apache Limestone

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Arizona Chris

Hello everyone!  We just finished our study of the diminutive bryozoans we found in the Fort  Apache east of Payson along the Highland Trail.  As expected, they are all very small indeed and tell us once again that the environment they lived in was a stressed  and sediment filled sea bottom, with little escape from the huge clouds of silt and sand raining down on them constantly.  Thanks for looking, and it is with great pleasure we share this write up with you!  (Adapted from our Paleo web site)


 For the amount of Limestone we have dissolved - now in excess of 200 pounds or so, it was surprising to only see about a teaspoon of bryozoans show up the acid fines.  But this is an additional clue to the conditions which deposited the Fort Apache Limestone.  As noted from write ups on previous batches of material, the amount of sand and silt mixed in with the limestone was a whopping 10%.  The source of course was the Sahara like dune complex on shore with its blowing winds and large amount of muds and silts washing into the sea.  The dune complex is now lithified into the adjacent Schnebly Hill formation, and forms  the gorgeous Permian red buttes seen in Sedona and surrounding areas.  Great for scenery, but at the time, bad for the marine fauna which had to deal with large amounts of sediment always raining down on the ocean bottom. 

This explains the almost complete lack of certain fossils, such as crinoids, brachiopods and corals.  These invertebrates cannot tolerate large amounts of sediments raining do on on them as it clogs their filter feeding apparatus, and will not be found in such areas.  Bryozoans were also filter feeders, and they are very limited in this formation, as are sponges.

We encounter three types of small bryozoans in the acid fines from the Fort Apache.  First, we have a branch or twig like diminutive bryozoan with extremely small pores over its surface.  These are some of the smallest bryozoans we have ever seen!  Second, a larger zooid type that encrusts shells and urchin spines.  These have excellent detail in each zooecium.  (the body chambers for each animal) And finally, fan shaped fenestrate bryozoans can be found in small broken pieces.  These net like "moss animals" have some very nice fine details in the fan segments.  Only a half a teaspoon of those were found, so are quite rare.

Here are some representative images of the bryozoans we have found in the Fort Apache Limestone, with magnifications that vary from 7x to 45x.


 Fenestrate bryozoans - 7x. These fan shaped colonies were always found in tiny centimeter or less sized fragments, and never larger. But they have excellent surface details on the zooecium side.



Closer view, with pin head at bottom for scale.



45x view showing small tube like pouches which contained individuals. These small tube like chambers are called zooecium in fossils and cystid for still extant living species.



Every small branching bryozoan we found can fit in a half a teaspoon. Some have Y shaped branching, others are straight or tapered. A pinhead for scale is at the bottom.



Some of the smallest members of this type seen here. Millimeter scale at bottom.



45x view of individual with very tiny pores.12.thumb.jpg.5f176001ad19c3a1f8cd4bf7cf28d2a2.jpg


The third type was a more robust larger encrusting bryozoan. This one covers the exterior of a broken urchin spine. Millimeters at bottom.



An urchin spine with a bryozoan partly encrusting its surface.



The largest encrusting specimen was stained red by oxides in the silica.



Encrusting type over a spine, showing detail in the zooecium.



Thanks again for looking, we are now starting work on sponges we found, a very few of them, but they are spectacular in micro details!




Living Bryozoans - Gary McDonald.


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Exquisite, the fenestrates are particularly beautiful and I've never seen an encrusted echinoid spine before.

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Arizona Chris

Yeah, I had never seen such a thing either.  Here are a few more I just shot (15 layers) that are not on the web site:


Bryozoan wrapped around spine, with serpulid on spine too:



Close up at 20x of above showing excellent zooecium detail:



Another bryozoan encrusting close to the tip of another urchin spine. at 10x - Better detail and more focus layers than the upper set:


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Great photos, I really must try stacking!  I believe that pre-Cretaceous "serpulids" like that are now all considered to be microconchids (I only found out recently, it's been mentioned on here a few times).

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Arizona Chris

Thanks, yes, its time to update the web site with the latest info.  But who doesn't like saying "spirorbis" ???  ;)

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