On Wednesday, Friday, and Saturday, I managed to get to my nearby site for more challenging rock splitting. On Wednesday, I found a second cephalon example of the lichid Acanthopyge contusa (see the update to my post here). Friday was a bust apart from the usual fauna, taking home only a few common proetid partials and a few unknowns that turned out to be nothing interesting when I got them under the microscope. Today (Saturday) seemed to make up for Friday's failure.
These are the tools that come with me in my backpack. I added the small pry bar today. Some of these rocks are veritable boulders that run deep, and since they are already extremely tough material to break, nothing comes easy. Even when the material doesn't shatter uselessly along a diagonal across the bedding planes, smaller chunks like to split vertically rather than horizontally as the beds can be so thinly packed and dense. Finding the right rock usually comes down to certain external features, but even then those can be blank duds or simply sparsely fossiliferous coral zones. Before committing to any larger rock, I test the edges to see inside first. The tool most often used in my arsenal at this location is the hand sledge.
When I say typical fauna, I mean the litany of fenestellate bryozoans, brachs, and trilobite partials. When I "test" the rock, these are the kinds of layers that usually show the most promise.
I am tentatively going to label this Acanthopyge contusa, although I am not fully certain it might not be another Terataspis as they have similar pygidial morphology. In some aspects, it seems to resemble both, but the preservation is not the greatest on this specimen. Going with the more conservative estimate, that would make Acanthopyge example number three.
Every split requires a careful scan so as not to miss something spectacular. I almost left it thinking it was a compromised brachiopod, but the notch on the bottom made me think it might be a hypostome. And, surely enough, it is a hypostome belonging to Terataspis grandis. Pictured on the right is the illustration by R.P. Whitfield (1897). That makes three examples of this rare lichid, although compared to those found by others and housed in museums, mine are all quite small. This example is barely 1 cm, while the one at the ROM is 7.5 cm. Still, a mini-monster is still a monster!
Sunday update: Spent another five hours out back and I would say these two partial examples of Acanthopyge contusa were the star finds:
Wednesday update: Another three hours as I steadily run out of viable rock. This is one specimen split between both halves of the rock. It is my fourth fragment of a Terataspis, specifically the genal spine. My tally now is two pygidia, a hypostome, and a genal. The likelihood of finding a complete one is along the same odds of winning the lottery, but how many trilobite collectors can lay claim to having even just a single fragment?
I'll be off this weekend to my secret Ordovician location up north, so I hope to post my finds when I return.
I've made a number of return visits to my local spot, but sadly have nothing remarkable to show for it. There is only one type of rock that is both fossiliferous and containing trilobites, and that rock type is a very thin minority at this location. I may have encountered nearly every example of it by now, including boulder-sized ones that make granite seem like butter when it comes to getting into without just creating powder and shards.
So my attention turns to other things, such as creating a kind of an updated master list of trilobites in Ontario. By drawing on the key sources, such as Ludvigsen and Isotalo (among others), this forms a basis for creating such a list. Formation names and taxonomic classification changes have been reflected in creating this list. I've added reasonable correlations based on similar strata in the US, both the Michigan and Appalachian basin. Those correlations appear in a separate column, and are not included in the Ontario species count until they can be found and confirmed in Ontario rocks.
I've also excluded Hudson Bay and James Bay trilobites on account of a lack of more sustained formal description. The list therefore only includes paleozoic rocks south of the Canadian Shield, or simply "southern Ontario."
I am told that there is some anticipated and ongoing taxonomic revision that may result in having to update this list, but revisions are to be expected anyway.
It should also be noted that more than half of these specimens could be classed as quite rare, or known only as fragments. Finding accessible outcrops remains the perennial problem for trilobite collectors and researchers in Ontario, and so even attempting to perform a reliable volumetric analysis of certain formations is imperiled by a lack of substantive sample size.
But this revised list is a good start which tells us something about the trilobite record here in Ontario. I expect to be updating this master list as new resources come available.
I've spent many days over the last two weeks scouring my new local site. I've pored over the literature and attempted to do a systematic analysis of the fauna in each of the rock types, taking extensive field notes. In terms of finds, not counting the numerous Crassiproetus pygidia and Pseudodechenella pygidia and cheeks, there are more days I go home empty-handed rather than dancing on air.
On the third consecutive day at this site, I managed to locate the right type of rock that is generally highly fossiliferous. This type of rock is in a minority at this site, and I've already split through any of the visible examples, leading me to dig under other large rocks in the hopes of finding more of the "good stuff."
The trilobites almost exclusively appear in rocks that contain large fenestellate bryozoans. The environment was shallow marine reef (owing to the massive presence of reef-builders).
Here is Terataspis grandis fragment number two:
I collected the positive and the impression. It is in pretty rough shape, but any fragment of this elusive lichid will come home with me. So is the matter settled about the strata being Bois Blanc? Hold on. Also in the same rock was this:
The top image is a capture from Rolf Ludvigsen's Fossils of Ontario Part 1: The Trilobites, and it shows a cephalon of the lichid Acanthopyge contusa. The image below is my find. But this is reported in the Amherstburg / Formosa Reef. This was already a bit confusing!
Terataspis is only reported in the Bois Blanc Fm. If this were Bois Blanc material, I have not seen even a trace of Anchiopsis in the large volume of material I've gone through. Acanthopyge is only reported in the Amherstburg, and although volumetrically the abundance of Crassiproetus is indicative of this formation, it is also a poor index given that it prevailed across several strata.
Riddles upon riddles aside, I am happy to welcome my second Terataspis, and a brand new lichid to my collection!
Stay tuned, for there is still a very large source rock for me to break down that weighs in excess of a metric ton. It is where the Terataspis was found. More to come this week, I hope!
Update, Sept 18, 2019
I found a second cephalon example of Acanthopyge contusa:
I am acutely aware that I'm back to work on Thursday, and so I've got just two more digging days left of summer. Tomorrow should see me back at my lower Devonian spot, and then a trip to Arkona the following day.
For now, cleaning up some odds and ends. First up is a quick prep job:
I'm being reunited with the other half of my Penn Dixie material on Wednesday, so there'll be more stuff to prep.
And now on to two drawings:
And that's it for me for now. Unless I have amazing finds in the next few days, my next update should be in the autumn.