Tuesday, May 31, 2011

Callipleura from the Hungry Hollow member

Callipleura is a genus that I was introduced to last year during my first visit to Arkona. I was searching the debris of the Hungry Hollow member of the Widder formation and found a nearly perfect specimen. A couple of the people I was with were really impressed with it so I gave it to one of them since I figured I could find more. When I went back a few weeks ago I did find more albeit not as good as that first one.

This first specimen is in matrix but part of the left side is missing. I like the hint of Aulopora growing near the edge.

This specime has both valves but it's been crushed nearly flat.

This is a smaller specimen and as far as I can tell it's a single valve

Another single valve half imbedded within matrix. The valve looks like it's in good shape that if I were to dig it out of the rest of the rock it's in I could have a decent specimen.

Sunday, May 29, 2011

Paracyclas from the Arkona Formation

A recent trip up to Arkona netted me a wealth of new genera from the site that I didn't have before. One of them was this Paracyclas that was found in the Arkona formation.

It's a steinkern (a mold of the inside of the shell) that has been completely replaced by Pyrite which is now altering to Goethite. This is the largest example I've found at this locality. I have another but it's much smaller, about 1-2mm in diameter.

Friday, May 27, 2011

Scalaripora sp.

While exploring the fossils that are eroded out of the Widder and Arkona formations I came across an odd looking bryozoan. It was not flat or round or fenestrate like most that I find there, instead it was three sided. I'd seen similar fossils before from the Pennsylvanian of Texas/Oklahoma in a genera called Prisimopora so I knew this wasn't an weird growth pattern or random occurrence.

This is the only piece that I have found of this genera so far and I don't know which formation it came from as it was at the bottom of a slope. Based on the "Check List of Fossil Invertebrates Described from the Middle Devonian Rocks of the Thedford-Arkona Region of Southwestern Ontario, STUMM, E.C., and WRIGHT, J.D. 1958. Contrib. Mus. Paleontol., Univ. Mich., Vol. 14, No. 7, pp. 81-132." There are three species found within the Arkona formation (S. approximata, S. canadensis, S. separata) but none in the Widder formation. Without close examination of this one specimen or the discovery of more I can't say for sure which species mine represents.

Wednesday, May 25, 2011

Lingula from the Arkona Formation

Lingula is a common inarticulate brachiopod that is known from the Cambrian all the way until modern times. It's a primitive creature that can survive in marginal environments. Perhaps this explains why is has persisted throughout time.

This is an example of the genera that I found eroded out of the Arkona Formation.

I featured Lingula in another post last year as seen here.

Monday, May 23, 2011

Tropidoleptus carinatus from Arkona

As I was sorting through my Devonochonetes sp. fossils, to find suitable examples to be photographed for this blog, I found one that didn't fit with the rest. It turns out this is my first example of Tropidoleptus carinatus from Arkona. It's a small shell at only 3-4mm wide so I'm not surprised I mistook it for a Devonochonetes at first.

What gives it away are the concentric growth lines near the edge and the wider, thicker radial ribs. Since I didn't recognize this when it was first collected I don't know for sure which formation it comes from. Based on this checklist from 1958 though, Tropidoleptus carinatus is only known from the Hungry Hollow member of the Widder formation.

Saturday, May 21, 2011

Cricoconarids from Arkona

Cricoconarids are fossil tubes that look like tiny squid shells or pencil points. They are mysterious fossils that are hard to categorize and considered problematic. Right now they are considered to be worm tubes or possibly related to jellyfish or corals. I've found two types of these enigmatic fossils at Arkona.

The first is Styliolina fissurella which are usually so tiny that they are often overlooked. They are small (1-2mm) smooth shells that look like miniature Belemnites. The fossil below represents hundreds, possibly thousands of individual shells that were washed together, by currents likely, into a small shoal which then fossilized. It was found washed out from the Arkona formation.

The other is Tentaculites which is well known from the lower Paleozoic. I wrote about some chunks of matrix that I found a few months ago that were packed full of Tentaculite shells here. Tentaculites are larger than Styliolina fissurella and have regularly spaced, raised growth rings along the length of the shells. I found this paper on Tentaculites from Poland, while researching Styliolina, that even breaks them, down into species and shows a cross setion through the shell. This first picture shows two examples of individuals that were found in the Arkona formation (top) and Hungry Hollow member of the Widder formation (bottom).

It's easiest to find and recognize Tentaculites within the Arkona formation. Here they can be found commonly associated with Mucrospirifer arkonensis, Devonochonetes sp. and individual loose columnal sections from crinoids.

Thursday, May 19, 2011

Devonochonetes sp.

One of the more common brachiopods to be found at Arkona is Devonochonetes sp. which is a small Strophomenid. It is very common at certain horizons of the Arkona and Widder formations.

This is a large example of the genera from the Arkona formation. Note the bumps along the hinge line which is a diagnostic feature and I may be able to use them to narrow down the species.

This is a smaller example that I believe comes from the Widder formation. This may also represent a different species from the example above judging from the radial line ornamentation on the surface of the shell and deeper curvature of the valves.

The size difference does not represent any known correlation between the formations, these specimens are a random sampling of the dozens of specimens I've come across. Below is a (literal) handful of specimens from both formations.

Tuesday, May 17, 2011

Ambocoelia umbonata from Arkona

I have found just one specimen of this next brachiopod at Arkona: Ambocoelia umbonata.

Within the Windom Shale of New York there are thin layers with hundreds of these brachiopods and examples of them can be seen in my previous post here.

Sunday, May 15, 2011

Athyris spiriferoides

One of the more common brachiopod fossils from the Devonian is Athyris and they can be found at Arkona as well. Below are some Athyris spiriferoides shells from the Hungry Hollow member of the Widder formation.

Edit 01/17/14: I now think that the above specimen is A. vittata while the below specimen is A. spiriferoides

While not as large as those found in the Wanakah shale (which is roughly equivalent to the Widder) they still show the typical concentric growth lines which mark this species. Those that I have found, within the Hungry Hollow member of the Widder, are often flattened or crushed. Hopefully one day I will find an inflated specimen.

Friday, May 13, 2011

Cyrtina from Arkona

Another common brachiopod from the middle Devonian period is Cyrtina. This is a triangular shaped brachiopod with a pedicle valve that is much larger than the brachial valve. I've found at least two species of Cyrtina at Arkona.

This is Cyrtina hamiltonensis with a very curved pedicle valve.

This is Cyrtina coultisorum which is much smaller than the above species.

There is a third species that can be found in the Arkona shale but I have not been lucky enough to collect one. Pictures of the above species can be found on the Friends of the UMMP website Here and Here.