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 spent the entire morning on Saturday at the hill & pit just beyond my backyard. My expectations were fairly low given how much I had picked the place clean over the years, so it was my goal instead to take pictures and record some of the fossil fauna there for posterity. How plans can get upended - sometimes in unforeseen yet lovely ways.
This picture is not exciting, nor was it meant to be! I began on the southwest portion of the hill (which is now pretty weedy with burdocks and spiky plants, by the way!). I had not spent a lot of time in that lower quadrant as I always seemed pulled to the upper southwest and southeast areas. Pictured here is a typical brachiopod assemblage - some spirifers, an atrypa-type, a Leptaena, and other assorted kinds. As I said, the purpose was to photo-document the typical stuff of the Bois Blanc Formation.
Another very typical assemblage from another distinct layer of the Bois Blanc. This tiny brachiopods can be quite numerous (I forget their name at the moment). So numerous, in fact, that some of the rocks bearing them actually are more shells than matrix, and just crumble. There are several examples of this type of assemblage in the area where the brachiopods are stained a kind of vermillion.
A similar assemblage to the first picture - some atrypas, a leptaena, and a large ?Strophodonta. Bored yet?
Performed a brief scan of the upper south quadrants and assembled a few of the specimens I had set aside from previous visits. If you zoom in for detail, you'll see, left to right, a rather chunky brach assemblage (name escapes me at the moment!), a lingulid pelecypod, a horn coral, and a typical (for particular layers in the Bois Blanc as a signature feature) cherty rock with a few corals showing cross-section. By this time, I had enough of the hill and was ready to give the adjoining pit another try.
Oh, but wait - I was distracted by a rock I had split and left behind some weeks ago. I decided to break it down to pluck two bryozoan specimens. The first pictured above is a typical fenestellate bryozoan. The next is a bit more peculiar...
Now what the heck is this? I made inquiries on The Fossil Forum, but at best we might describe it as Sulcoretepora. As described by a single specimen in the Amherstburg Formation by J.A. Fagerstrom:
"This specimen is a short bifoliate stem with three rows of apertures on each flattened side and none on the edges. Slightly raised longitudinal ridges separate adjacent rows of apertures. Apparently no mesopores are present between apertures but they may have been destroyed by recrystallization" (17).
Fagerstrom, J.A. (1961). The fauna of the Middle Devonian Formosa Reef Limestone of southwestern Ontario. Journal of Paleontology 35(1):1-48.
There are some interesting branching, radiating patterns in this one, with two zooecial apertures near the upper left and upper right corner (the dimply stuff). Colony form here is likely remnant of bryozoan encrusting substrate (with thanks for our experts on the forum). But why are we even talking about Amherstburg Formation? Let's keep this flagged for the time being.
I was not expecting to find any trilo-butts, but I managed to find about six. So now I am in the pit and can confirm that it contains Bois Blanc formation rocks. I dug this rock out of the wall of the pit, and pictured above is the pygidium of the dalmanitid trilobite Anchiopsis anchiops (which only appears in the Bois Blanc), but missing its full trademark pygidial spike.
Some in situ photos from the pit as I work the same rock. The top picture shows some typical assemblages, while the two lower pictures are closeups of the most frequent brachiopods.
Trilobite impressions (Anchiopsis anchiops). I took the positives home.
After I patrolled the rest of the pit and did not find much more to my liking, it was time to go home and take stock of the finds. Pictured above is a gastropod steinkern (the inner whorl occurs on the reverse side). Beneath that is a nicely inflated clam, and on the right is another spike-deprived Anchiopsis anchiops.
This specimen, found on the hill, is the real "meat" of this post. This is not a trilobite that appears in the Bois Blanc, but solely in the Amherstburg formation. The Amherstberg is a younger formation, contiguous with the Bois Blanc if there is no Sylvania formation intervening. Note the nodules on the fringe of the pygidium.
Consulting Ludvigsen's 1979 text, Fossils of Ontario. Part 1: The Trilobites, there is a specimen reported that looks nearly identical to this one, but it is simply called Dechenella halli. The name was updated by Ludvigsen in 1986 and recognized as a new genus: Mannopyge halli.
Here is a plate from the Ludvigsen 1986 text on the left, compared to my find on the right:
Quite exciting, as this makes the 19th species of trilobite in my expanding collection (I've more than doubled it since March of this year alone). Let's learn more about it:
"A warburgelline with pear-shaped glabella, deep sigmoid 1s furrow, narrow (tr.) and faint 2s and 3s furrows; no preglabellar field, tropidium, or tropidial ridges. Large eyes located anterior of cephalic midlength; genal spines short. Semicircular pygidium iacks a flat border,-axis with 9 - 10 node-bearing rings, eight faint pleural furrows and incised interpleural furrows, each pygidial rib terminates abaxially as a rounded node isolated by moderately deep paradoublural furrow. [...] No other warburgelline has a semicircular pygidium, and none possesses a conspicuous row of fringing nodes such as that of Mannopyge. The pygidial pleural ribs of M. halli, however, are of the flat-topped warburgelline-type (Owens 1973, Fig. 2), and there is no reason to doubt that Mannopyge is a late member of the subfamily Warburgellinae." (Ludvigsen 1986, 683).
Ludvigsen, Rolf (1986). Reef trilobites from the Formosa Limestone (Lower Devonian) of southern Ontario. Canadian Journal of Earth Sciences (24): 676-88.
Two remarks: First, this tells me that there are some Amherstberg formation rocks in the mix at this site. Second, trilobites in the Formosa reef limestone are not particularly common, dominated as it is by coral and stromatoporoids. Of the uncommonly found trilobites in that limestone, it is mostly dominated by Crassiproetus, followed by frequency occurrence Mannopyge halli, followed - in descending order of frequency - by Mystrocephla, Acanthopyge, and Harpidella.
I'll leave off today with a few more pictures, mostly to underscore that my picture-taking ability has seen a little boost in quality on account of having acquired the third-party app, Camera+, so that I can take proper macros. Using an iPad to take closeup images can be a bit unsatisfactory, but the app I purchased allows me to get in much closer and increase the resolution (which is probably why those of you with slower bandwidth are cursing me right now). As a test, pictured above are two sides of the same piece of crinoidal limestone found at Penn Dixie.
And this is a closeup of a coral piece from Arkona. I'm pleased with the detail.
Ok, enough from me until next weekend, when I'll be headed to a quarry east of Lake Simcoe for some serious Ordovician collecting. Until then, thanks for reading!