Hyperoblastus filosa

Blastoids are a cool fossil to find and previously I thought they only could be found in Carboniferous aged rocks. It wasn't until I visited Arkona and spoke with local expert Joe K. (Crinus on the Fossil Forum) that I found out otherwise. During my visit to Arkona last fall I got lucky and found the below specimen of Hyperoblastus reimanni filosa.








The Blastoids from Arkona are very small and must be found while crawling on the ground or by getting lucky and screening the fossil gravels formed from the weathered rock of the formations. I found this at the base of a slope along the Ausable river in an area of washout gravel that had eroded from the Arkona formation.

Mucrospirifer arkonensis

I'm heading back to Arkona, Canada soon so I plan to feature a series of fossils that I've collected before at this prolific site. I've only had a chance to visit it twice but have brought back a wealth of fossils, many of which I can't find in my local rocks.

As a refresher, Arkona is a small town in Ontario, Canada that is close to an exposure of Middle Devonian aged rocks along the Ausable river. The best exposures are along an area called the "Hungry Hollow" but what meaning that was once associated with that name has long since been forgotten. Both Arkona and Hungry Hollow lend their names to the formations that are found in the exposures along the Ausable river and so the fossils generally come from the Arkona formation or the Hungry Hollow member of the Widder formation. The fact that the Hungry Hollow was once considered a formation but has since been reduced to a member of a different formation is a point of contention among local collectors.

So to summarize, Middle Devonian (Givetian) aged rocks exposed along the Ausable river near Arkona in Ontario, Canada.

Today's specimen is Mucrospirifer arkonensis which comes from a bed within the Arkona formation. It has a very this body that is very wide and almost looks like a straight razor.






Typically I find these covering the top of a layer of fossil hash and the above specimen is the first (mostly) complete, loose shell I've collected. Below is a typical presentation which, if you are willing to haul the chunks back to your car, makes for a nice garden rock.



Due to the large number of remains one gets a better idea of how large some of these shells got. A couple of just single valves and you can see the interior architecture of the muscle attachment points.




The layer looks like a storm deposit due to the jumbled remains. A side view of the layer shows that I mean.



Some of the other fossils that are found in this layer are:

Devonochonetes sp.


Sulcoretipora


Tentaculites

Rastellum gregareum from France

Rastellum gregareum from the Upper Jurassic (Oxfordian) cliffs along the English Channel called the Vaches Noires (Black Cows). These specimens were sent to me by my friend Gery and were collected by him near Villers sur Mer in the providence of Normandy, France. I love the random, crenelated look of the shells of these oysters. They kind of look like a topographic map of a drainage basin in some cases. Some species get long and curved and are nicknamed "Denture Clams".







This specimen has the ridges coming from a more central line as opposed to along the edge as in the last specimen.




This one must have anchored to another clam shell as it seems to have grown upwards from the base and reminds me of a flower pot.

Giant Straparollus

I guess it's true when they say that "Everything's bigger in Texas"! Here is a giant gastropod from the Pennsylvanian; Straparollus (euomphalus) plummeri. This specimen was found in Brookesmith, TX back in the 1970's and comes from an old collection. I've seen specimens of Straparollus before but mostly they were small, 1-2 cm sized specimens while this is more like 6-8cm in diameter. I'm not exactly sure what formation this came from as there were not much details on the label except the location.







I detailed some other Straparollus in This Post about gastropods from the Finis Shale in Texas.

Lima wacoensis from Texas

Lima wacoensis is a pelecypod found in the Lower Cretaceous aged (Albian stage, 105-108 mya) Goodland Fm. of Tarrant county, Texas. It is ornamented with ribs that radiate from the umbo (beak like portion at the back of a pelecypod shell) and has very fine, concentric growth lines.









I purchased this fossil from Dan Woehr who seems to know every fossil exposure in Texas! Check out his collecting reports at The Meanderings of a Texas Fossil Hunter site which is a part of the Brazosport Museum of Natural History's Web site. While he won't give out the locations he hunts, he does a decent write up of what he finds and has loads of pictures.

Fossil crab Xanthosia from Texas

Another fossil crab from Texas is Xanthosia pawpawensis. These specimens were found in the Lower Cretaceous (Cenomarian stage, 97-98 mya) aged Pawpaw Formation. in Tarrant County, Texas. I received them in a trade with Herb M. who collected them himself. Thanks Herb!


Specimen #1



Specimen #2




I got the age info for the formation from Lance Hall's website North Texas Fossils. He has pictures of fossils he has found in the formation and some good information about the geology of the Paw Paw formation and the region in general.

Fossil crab Notopocorystes from Texas

Here is a fossil that is identified as a Notopocorystes fossil crab. It comes from the Eagle Ford Group which is part of the Cenomarian stage (about 94 mya) of the Lower Cretaceous and was found near Dallas, TX. As is typical of most fossil crabs found in the field, only the carapace is well preserved. However, you can see a small cross section of a leg in the lower right portion of the piece in the third picture. Looking at the piece it seems to have been a nodule at one point as the bottom is well rounded.





I found the age info for the formation from Lance Hall's website North Texas Fossils. He has pictures of fossils he has found in the formation and some good information about the geology of the Eagle Ford group and the region in general.

Blastoid with brachioles

Blastoids are a common fossil from Carboniferous aged rocks but rarely do they have their brachioles (feeding organs) preserved. This specimen, which I purchased on E-bay, has some brachioles preserved in near life positions.







Unlike Crinoids, Blastoids had very short cillia like arms (brachioles) that lined the edges of ambulacrul grooves (the five petal shaped areas) on the theca (body of the animal, similar to the crinoid calyx). This specimen has parts of those presevred with it which indicates a very rapid burial with little disturbance afterwards. Most blastoids are found without the brachioles because after the animal dies they fall apart at the joints and scatter in the currents.

Hybocrinus nitidus

From the Ordovician aged Bromide formation of Oklahoma come these Hybocrinus nitidus. These hail from an odd group of primitive Echinoderms that may be precursors to Blastoids. I can't find too much basic information on them on the internet and anything more specialized are in professional journals.

You can clearly see the five fold symmetry when looking at the top of the calyx. The wider, triangular area near the top might be where the anus was located(?).





Another specimen



The narrow openings on the top of the calyx are where I presume the brachioles (feathery feeding fingers) would have been as there is no clear anatomy to suggest arms as in traditional Crinoids. If anyone knows more about these interesting creatures, please fill me in.