Partial placoderm plate from the Arkona formation

I have never found much in the way of fish remains at Hungry Hollow, Ontario, but once I did find a small fragment from a bony placoderm plate.  Placoderms were early, shark like fish that had external bony armor around their heads. There are a few species known from the middle Devonian aged rocks found at Hungry Hollow (Arkona formation and Widder formation) but this is just a fragment so I doubt I could narrow the species down.

I found this piece near the base of a slope of eroded Arkona formation and could not find any trace of more uphill. You can tell it is bone due to the pale blue color (evidence of the phosphate mineral Vivianite) and the spongy structure within the piece.

Top surface - this is what would have been the outer facing portion of the bone. Note the bumps, perhaps they helped streamline the fish for swimming purposes?

Two side views of the bone showing the spongy nature.

This was the interior side of the bone

I collected this specimen from the Arkona formation which is Devonian in age, Givetian stage.

Clionolithes sp. borings (?) in M. arkonensis shells from Arkona

A trip to Arkona last fall yielded a fine specimen of Mucrospirifer arkonensis that is perhaps the most complete specimen I've found to date. I found it while attempting to traverse the always slippery Arkona formation (Devonian, Givetian stage) and noticed it sticking out of the hillside. It also shows signs of another kind of trace fossil that I've not seen before. Here is the shell fossil showing that it is about 90% complete missing only the very tips of the wings that project along the hinge line. But notice also the little pepper like flecks that are scattered across the surface.

A closer view of those flecks show that they are, in fact, trace fossils from some kind of burrowing organism. Interestingly, they appear to be concentrated in the brachial valve and seemingly spread from the hinge line towards other parts of the shell.

A closer view

In doing a little research they look similar to borings that a sponge would make and there is a known genus,  Clionolithes, that has been erected to account for these. Most of what I can find on Clionolithes is based on fossils from the upper Devonian and speaks of radiating or branching features. The specimen I have does not appear to show clear lines that radiate from a central point but they do show some evidence of branching occasionally. As I study them they almost appear like stitches in cloth whereby the burrow seems to rise and fall through the shell. Perhaps these are actually worm borings rather than sponge but I can't find any good info to indicate other wise.


I found a second specimen on that same trip that shows similar markings along with some Aulopora elleri on the surface.

Hopefully I will find more specimens with this feature on them during future trips to Arkona. I'd like to see if they are isolated to M. arkonensis or if they also appear on other species.

The only other evidence of boring sponges that I personally have found are of Cliona cretacica on oyster shells from the Cretaceous sediments of Delaware and New Jersey.

A new specimen of Productella spinulicosta from Arkona

Another cool fossil find from last fall at Arkona is this Productella spinulicosta brachiopod with some of the spines still intact. I found it on a weathered slope that exposes both the Widder and Arkona formations (both are Devonian, Givetian stage) so I can't say for sure which set of rocks it came from. Previously I've only found specimens of this species with no intact spines.

Playtceras spinosum gastropod on Arthrocantha crinoid calyx from Arkona

About three years ago I posted some pictures of a Platyceras sp. gastropod that was fossilized on top of an Arthrocantha sp. crinoid calyx that came from the Silica shale in Ohio. This past fall I found a similar fossil at a site near Arkona, Ontario, Canada. The specimen came from a weathering pile of Arkona shale (Devonian, Givetain stage) and was found on the surface.  The gastropod has a few circular openings on it's shell that I interpret as being the bases for spines so I should label it as Platyceras spinosum. Update 01/24/15 - thanks to the comments of a reader I was reminded that spiny specimens of the gatropod Platyceras are now called Spinyplatyceras arkonense.

 

There are a couple of bryozoan epibiont patches on the Platyceras shell as well but I am unsure of the species. Possibly Paleschara incrustans?

Scalaripora canadensis bryozoan from the Arkona formation

A couple of years ago I found a small, isolated specimen of Scalaripora sp. from the Arkona formation. On a visit this past fall I found two more pieces that are larger than that first piece. Both have the same thin, tripartite growth pattern but there is enough present that I think I can narrow the species down to S. canadensis. I base this upon reading an old text: "Contributions to Canadian Palæontology, Volume 1" By Joseph Frederick Whiteaves, Montreal, 1885.  Page 378 has the following description and plate 48 has an illustration. 

"Zoarium consisting of stems that are triangular and almost equilateral in transverse section, the broadest of the three faces having a maximum diameter of about 7.5 mm, and the narrowest of 6.5 mm. Faces shallowly concave or nearly flat: angles acute forming three sharp, prominent, and nearly straight but rather irregular, longitudinal ridges. Transverse ridges distant, nearly as far apart as the faces are broad, not continuous in either of the two fragments examined, developed (or present) on two of the faces in the longer of these fragments, and on only one face in the shorter. Whole surface celluliferous, apertures averaging from about 0.16 mm to 0.25 mm in diameter, usually rather more than their own diameter apart, or about equal to it in distance, subcircular with a slightly elevated annular peristome and arranged obscurely in more or less regular diagonal rows, seven or eight in three mm. Internal structure not observed. "

Specimen #1

Specimen #2

Leptotrypella quadrangularis bryozoan from the Arkona formation

At the site near Arkona, Ont., Canada where I go to collect fossils from the Arkona and Widder formation, there is a large pile of excavated clay-stone from the Arkona formation. The rock is quarried for use in brick making but needs to be weathered some before it is used. On this pile I found a piece of bryozoan that belonged to a larger colony of Leptotrypella quadrangularis. This is a new species for my collection.

It looks very similar to Atactotoechus fruticosus but the monticules (the raised bumps on the surface of the fossil) appear to be slightly taller.

Quasillites concentricus? Ostracod from the Arkona shale

Here are another couple of Ostracod fossils from the Arkona Shale. They are Quasillites and I think they are Q. concentricus. They stand out because of the fingerprint like pattern on the surface.

I found the above specimens from a piece of the Arkona Shale that I soaked overnight in some water and then screened. The Arkona Shale is middle Devonian in age (Givetian stage).

Poloniella cingulata ostracod from Arkona

Here is one of the Ostracods I have been able to identify from my Arkona screenings. I think they are Poloniella cingulata. This is a species that is listed in the "Checklist of Fossil Invertebrates Described from the Middle Devonian Rocks of the Thetford-Arkona Region of Southwestern Ontario" by Stumm and Wright.

I found the above specimens from a piece of the Arkona Shale that I soaked overnight in some water and then screened. The Arkona Shale is middle Devonian in age (Givetian stage).

Screening the Arkona shale for microfossils

I ran a sample of the Arkona shale through my screen set to see what I could find. I didn't look too long or closely as this was meant to be a dry run or proof of concept test.

This is the rock sample that I used. Note the Phacops fossil, you'll see more of it later.

The Arkona formation is mostly clay and readily breaks down when in contact with water. In preparation for this experiment I left the chunk of matrix in some water for 24 hours to let it completely break down.

It took about a hour to get all the screening completed, the biggest obstacle is that the water will become saturated with clay while washing and needs to be replaced. So far it has been much cleaner and easier to do all the screening outside with a bucket of clean water to occasionally rinse the screens through.

Here are the results. From the #35 screen I found at least two species of Ostracod, lots of Tentaculite pieces and bits of the Trilobite that disintegrated while the clay matrix broke down.

The #60 screen had smaller bits and pieces (as is to be expected) along with some possible Ostracods but nothing that I was able to easily pick out and ID...

A Styliolinid...

Part of a Conodont/Scolecodont....

And other stuff.

Now we are getting to the really tiny stuff. The #120 screen material looked like this:

 and the #230 screen material looked like this:

I took all the above photo's with my Zorb digital microscope but that only magnifies to 20X. To see anything meaningful in the #120 and #230 screens I would need a real microscope.

So the experiment was a success and I've learned a bit about how to best screen samples of clay matrix material. My next experiment will be with eroded Silica Shale from the dump piles near Sylvania, Ohio. The step after that will be to figure out the best way to separate the tiny samples for the fossils I want, ID what I find and then store them so they don't get lost.