Phacops Rana from the Silica Shale

While exploring the eroded dumps of Silica Shale at Sylvania I happened upon the largest Phacops trilobite fossils I've ever found.

Here is an enrolled specimen, about the diameter of a silver dollar, with pyrite crystals forming on the eye lenses.


It's not a perfect specimen as some of the glabella (the part of the cephalon of a Trilobite that is between the eyes at the very front of the head) is missing.




I find it interesting that the pygidium of this animal looks like it's missing at first glance. But you can see that it's just separated and rotated inside the rest of the shell.



Here is another specimen that is enrolled. Not in as good a shape as the previous fossil but all the bits are there.







Finally there is this prone specimen that is also not in the best condition as the glabella and the left half of the cephalon is entirely missing. The fossil is about three inches long and is the largest Phacops fossil I've ever found.

Aulocystis from the Silica Shale

A cousin of Aulopora is Aulocystis. This is easily distinguished from the former by the fact that colonies don't encrust shells. Rather they grew as single branching colonies or as dense colonial clusters.

Here are some of those cluster type Aulocystis fossils






From studying the 1975 book by Robert V. Kesling & Ruth B. Chilman: Strata and Megafossils of the Middle Devonian Silica Formation: Museum of Paleontology, Papers on Paleontology, No. 8, pg. 54, pl. 43, 45, I believe that the above fossils can be called Aulocystis auloporidea.

Aulopora from the Silica Shale

Another common Epibont found on shells from the Silica Shale, and Devonian in general, is Aulopora. The 1975 book by Robert V. Kesling & Ruth B. Chilman: Strata and Megafossils of the Middle Devonian Silica Formation: Museum of Paleontology, Papers on Paleontology, No. 8, pg. 56, lists only one species that can be found within the Silica Shale: Aulopora microbuccinata. Aulopora is a species of coral and bears a similar growth pattern and overall look to the Bryozoan Hederella. The easiest way to tell them apart is that Aulopora is much larger.


Here is some growing on a Paraspirifer





Another colony on a Mucrospirifer


Another colony on a shell fragment



The corallites of Aulopora are thin walled and sometimes they are easily broken open by the erosion process.

Hederella from the Silica Shale

Hederella is an epibont which is a non parasitic organism growing upon another animal, most often a shell. It is a genera of Bryozoan within the Cyclostomata order and has at least 12 species within the Silica shale according to the 1975 book by Robert V. Kesling & Ruth B. Chilman: Strata and Megafossils of the Middle Devonian Silica Formation: Museum of Paleontology, Papers on Paleontology, No. 8, pg. 58, 61.

As I've mentioned before, trying to ID down to species level in Bryozoans is difficult so for now I am just going to associate them with their genera name, Hederella.

Some winding colonies on Strophodonta shells




The host shell for this colony is Megastrophia



Hederella is an eye catching epibont forming colonies that look to me like detail stitching in a quilt. When I find a shell with them growing on it I'm more likely to toss it into my collecting bag because of the interesting look.

Here are some closeups I took with my Zorb digital microscope.

Heterophrentis from the Silica Shale

Heterophrentis is a common rugose coral found throughout much of the Devonian. I've found a couple of specimens that I think are Heterophrentis simplex on the Silica Shale dumps in Sylvania.







Another, larger specimen that shows some crushing. I'm not sure when the damage occured, before or after burial.







My ID is based on the 1975 book by Robert V. Kesling & Ruth B. Chilman: Strata and Megafossils of the Middle Devonian Silica Formation: Museum of Paleontology, Papers on Paleontology, No. 8, pg. 47, pl. 3, 4, 6.

Cayugaea from the Silica Shale

Cayugaea is an interesting rugose coral that I've struggled to ID since I first found two specimens on the dumps in Sylvania. It's odd to me because the shape of the body starts narrow and stays that way until suddenly widening out whereas most rugose corals have a smooth, constant growth pattern with the body widening as the animal grows.





When you look at the calyx (the cup shaped area at the top of the coral where the animal lived) is has convex, bubble like tabellae lining the interior. These structures are similar to Cystiphylloides which is also found in the Silica Shale but has a more traditional gradual widening growth pattern.



A view of a cross section through the "neck" area shows the same tabellae lined the interior of the coral.


Thanks to the 1975 book by Robert V. Kesling & Ruth B. Chilman: Strata and Megafossils of the Middle Devonian Silica Formation: Museum of Paleontology, Papers on Paleontology, No. 8, pg. 51, pl. 3, 6. I am confident that the above specimen is Cayugaea intermittens.

Philhedra from the Silica Shale

Another common inarticulate Brachiopod is Philhedra. This brachiopod is identified by the flat cone shaped shell with fine radiating ribs from the central peak.






The presence of these epibont fauna Brachiopods lets you know that the bottom of the sea floor was not always turbulent. Were it so then the host shells on which they lived would be constantly flipped over and possibly smother the parasites. Another inference is that the host shells were exposed for some time, years possibly, before burial during a storm event. Good evidence for the Catastrophism point of view which states that the fossil record records short, dramatic events rather than a gradual constant progression (otherwise known as Uniformitarianism).

Petrocrania from the Silica Shale

Some inarticulate Brachiopods attach one of their valves to a hard surface and lift the other valve like a cap. One of these oddballs is called Petrocrania and is commonly found on various shells within the Silica Formation. The shells are very plain with no real decoration so they sometimes look like a scab on the surface of a shell. Some even grow their shells to match the external ribs of their host shells.









This Petrocrania was in turn colonized by a Bryozoan (possibly Atactotoechus sp.). All you see on the underside is the interior of the top valve.