A short post today before I'm off for three days at three different quarries.
So I spent the latter half of the morning at my usual spot just beyond my backyard, cracking rocks in the rip rap pit. There is a wide variety of formations present, all of them in a big jumble. I do know that they largely span the early to mid Devonian. I was not expecting to find much as I've been there so many times that it has become the victim of my picking it over! However, surprises still happen on occasion.
A new entry to be included in the trilobite gallery. Initially, I thought this was just another Anchiopsis anchiops, as their tail fragments are among those I find on occasion in these rocks. But it is not quite right. These are images from Rolf Ludvigsen's 1979 book, Fossils of Ontario: The Trilobites. The one on the right is the closer match: Coronura aspectans, which is found in the Dundee Fm.
.How I can suspect it is Coronura is based on a few observations: 1. The pygidium of my specimen does not taper in the same way as an Anchiopsis; 2. The number of pleural pairs is very high; 3. The axial lobe is relatively thin; 4. There seems to be small concavity at the pydigium's edge that would either have been a single spike (no) or the two-pronged spike of a Coronura.
And so, as tentatively confirmed by my TFF friend, Don, I'm going with Coronura aspectans. Awesome!
*****But wait, there's more!*****
Actually, the tentative ID is incorrect. It was tentative, just for the record, based on a poorly preserved specimen. Scott, our trilobite expert on TFF, has given the ID as Trypaulites erinus from the Bois Blanc Fm. Not a new genus for me, but definitely a new species. Here is the picture Scott referenced, put next to another image of my specimen. We have a dead ringer!
So, a few things to mention here. T. erinus is described in "STRATIGRAPHY AND PALEONTOLOGY OF THE SYNPHORIIDAE (LOWER AND MIDDLE DEVONIAN DALMANITACEAN TRILOBITES)" by Pierre Lesperance (thanks again to Scott for the reference, and from where the image above comes).
Second point being that this specimen is only known by its pygidium; no other parts have been found. I suppose there is a chance that this is not a common find.
This year has had a lot of these moments where I seem to find uncommon/rare trilobites for which only fragments are known - or, in some cases, no specimens have been recorded where I found them (but they are described in equivalent units elsewhere). Finding fragments may seem like a bummer, and a lot of fossil collectors would pitch them aside in search of a full specimen, but there are specimens out there so rare that finding a fragment is a significant event.
It looks as though the "rip rap hill/pit" behind my home is a veritable trove of uncommon specimens. And to think, several years ago, I just ignored a lot of the rock there or assumed it was just dull Dundee stuff. I've now found five distinct genera at this location, and I can only hope more rock gets exposed for me to split. At the same time, trilobites are not abundant at this location; many have been the trips when I came back skunked without even a trace of trilobite, and I would say it is now about 1 in 5 trips that I find even a single trace. But I need more weathering and exposure. I am pretty much running out of rock to break, and spending my time sifting through tiny shards of my own previous visits is unlikely to make for a lot more winning visits.
So today I decided to spend part of the morning at that site near my house, the infamous "riprap hill" and associated pit. I've long suspected most of the rocks I split there were trucked in, and have confirmation of that due to the three different kinds of trilobite I've pulled from it (two in the last four months - Anchiopsis anchiops and Mannopgye halli).
I had been finding examples of rock from the Hamilton Group, Dundee Formation, Bois Blanc Formation, and the Amherstberg Formation. A good and wide range of Devonian age rocks.
As can be seen above, the usual assortment of brachiopods and a gastropod. My expectations were low as I'm running out of rocks to break after four years of scouring the place.
Ok, but what about this? I get the line by Morpheus in the Matrix in my head saying "what if I told you everything you knew was a lie?" So at first I was in disbelief: this must be a shell impression, not the impression of a trilobite pleura. But I've seen this before. In the Ordovician. Yes, it is a fragment of a Pseudogygites. The nearest Ordovican outcrop is 300 km away.
If I needed further proof, I flipped over this piece of shale and saw a fossil barely bigger than the head of a pin. Putting it under the microscope, it is indeed the cranidium of a Triarthrus.
Oookay, then. Confirmed: dumped rocks that span over 100 million years. From a field perspective, this is going to make things much tougher in terms of certainty over finds, but I suppose it means a veritable potential bonanza of finds spanning a much broader range of geologic history.
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!
Now that the course I was teaching is done, and the heavy rains are behind us, thoughts turn back to the hunt. The heavy rain system that lashed a lot of Ontario and western Quebec left a great deal of flooding. Fortunately, not as much here, but the rivers and lakes had been dangerously high, making any collecting near them too dangerous.
But as it is the long weekend, Deb and I got out to Arkona for a five hour hunt. Overall, not a hunt that bagged the best specimens, but we weren't skunked either.
This is the north bank. The photo does not show the proper scale for the bench I worked out. It was already started by someone else, but I was able to lever out two enormous slabs weighing maybe 300-400lbs each. The slabs were partially covered by overburden, so I underestimated their size until I started seeing a crack. But with a lot of grunting and levering with the pry bar, I freed them and rolled them down the hill to be worked on.
Anyone who has worked the Widder shale before knows all too well that one has to go almost quite literally through tons of it to find a full Greenops. Instead, hundreds of moulted bits are quite plentiful.
There are layers in the Widder almost entirely dominate by spirifer brachiopods, but they are trilobite-poor.
Patience and a lot of hammer blows / rock busting can be rewarded. I was able to call first blood on a likely near-complete Greenops widderensis after a few hours working the slabs. Sadly, this one is tucked in the matrix (but can be worked out) and is missing a chunk of its right cephalon.
But it seemed a pretty good day for nautiloids. Pictured above are three Michelinoceras sp.
This one may be a bit more of a challenge to make out, but if you look closely you can see the spiral shape, with a bit of the texture showing in the upper left (the brassy, pyritized stuff). This would be a Goniatites, and a fairly large one for this strata.
And last up: Deb found her complete Greenops (also tucked in matrix, but in better shape than the one I found). On the right is another semi-inflated pyritized Michelinoceras that I'll have to chip out of the rock.
Pictured above is a before and after picture of the nautiloid I found, prepped with a Dremel. Came out fairly well, but this is as far as I dare to take it using an engraver. One day, air scribes and compressors will be needed!
So that's about the long and short of the five hour Arkona trip. Below are some other odds and sods:
Paid a visit to my local rock shop run by two very nice folks. I picked up these two Flexicalymene ouzregui (Ordovician) from Morocco's Anti-Atlas mountains.
A busy brach hash plate from the Bois Blanc Fm fill out in my back nine.
Nice big brach + impression from the same area.
And lastly, another example of Anchiopsis anchiops - pygidium missing its pygidial spike. Lower right I suspect is just a worn and partially buried Eldredgeops rana. Below is a close-up of the Anchiops with some diagrammatic details provided by our Fossil Forum's resident trilobite expert, Scott. "Anchee," as I will call it, is a dalmanitid trilobite, and the way to tell it is by such an incomplete specimen would be the incised axial rings, shown by the arrows in the re-cropped photo below:
I actually didn't anticipate posting again until after the upcoming dig at Penn Dixie, but two consecutive days of collecting at my riprap hill nearby has brought some excitement into the collection.
For some many years of collecting from this place, I knew a lot of that material was shipped in. My assumption was that it was more locally sourced (and thus mostly Dundee Formation). Many of the fossils I was pulling from there are reported as part of the Formation. Until I found one that wasn't. But also peculiar were the fossils I was NOT finding that are typical of the Dundee. Not even typical of the Hamilton Group (Arkona, Widder, etc.). I guess I was blinded by what I assumed to be true as opposed to facing the cold, objective truth as evidenced by the biota.
Yesterday I found this:
And a closer view:
So, fairly eroded away, leaving only a cast/mold of a part of the cephalon of this trilobite. But it is a whopper. I don't really find Devonian trilobites approaching this size (Ordovician ones, yes). So I posted it on the fossil forum, and our resident trilobite expert Scott weighed in and said it was either Trypaulites calypso or Coronura aspectans, both of which are recorded in the Dundee Formation. There isn't a lot of diagnostic details to go on, but you can make out the distinctive occipital ring and the deep furrow on the lower left of the cephalon. So, we know it could be one of these two dalmanatid trilobites, right? Hold on...
I spent another four hours today carefully taking on any rock on the hill, splitting it, and seeing if anything interesting might come up. As I've pulled Basidechenella from there in the past, I was hoping for more than just another pygidium. There was this one greyish, round rock about the size of a softball lying there. I wasn't going to bother with it as I thought it would just be another blank, or just one of those dense balls of largely erosion-resistant rocks where you have to bring out the big guns to split it and find only a tiny smattering of brachiopods. But I was already sitting in the gully breaking rocks, not in a hurry to get back up, so I thought, "why not while I'm here?" So glad I did, because this was the rock that became the key for determining the origin of many of the rocks on this hill - and thus explains the biota.
Without double-checking, I thought, "ok, another Trypaulites specimen. That's pretty lucky to find two in less than 24 hours." I assumed from my patchy memory of looking at a Trypaulites in the Ludvigsen volume. I really should have looked more closely to confirm that assumption. I was still tickled pink to find another specimen. But when I posted it, Scott chimed in again by saying it was NOT a Trypaulites. It was instead a Anchiopsis anchiops, and those only occur in the Bois Blanc Formation.
The only significant outcrops of Bois Blanc are hundreds of kilometres away, in the Niagara escarpment. So what the heck was it doing here in London, Ontario? There is no doubt on the ID of this one. I checked the literature and, Scott was bang on as usual. Scott then revised his earlier ID on the big cephalon above and said it was also Anchiopsis, but missing the distinctive occipital spine. Here are the images Scott presented for comparison with what I found:
So I went back and took a longer look at the several finds I've made in this location over the past four years. I compared those to what was listed in the Bois Blanc, and there they all were. What didn't tip me off is that there is a great deal of overlap of species between the Bois Blanc, Dundee, and other formations in the Devonian. For example, the trilobites Eldredgeops rana and Basidechenella sp. appear in both formations. I had reasonably assumed that the materials delivered and dumped to make this hill would be more locally sourced, as that would seem more economical. And thus I stuck with my first assumption that everything I pulled out of the hill was likely Dundee Formation or thereabouts. But the presence of the Anchiopsis throws all of that out, as it ONLY appears in the Bois Blanc. So, in sum, I am collecting from the Niagara escarpment pretty much in my backyard. The stratigraphy is as follows in descending order of age:
The Bois Blanc is the second oldest Devonian strata, underlain by the Oriskany. According to Armstrong and Dodge (2007):
"The Oriskany Formation is disconformably overlain by the grey to brown, very cherty, fossiliferous, argillaceous limestones and dolostones of the Bois Blanc Formation (Uyeno et al. 1982). Thin beds of glauconitic quartz sandstone that occur near the base of the Bois Blanc are assigned to the Springvale Member (this member is not shown on OGS maps). The Bois Blanc Formation outcrops and subcrops in a narrow belt from Fort Erie on the Niagara River to MacGregor Point on Lake Huron. North of Norfolk County outcrops of this unit are sparse."
According to Ludvigsen (1979), there are five major genera of trilobites in the Bois Blanc: Phacops [Eldredgeops] rana, Basidechenella sp, Crassiproetus sp, Anchiopsis anchiops, and Terataspis grandis. I have so far collected three of the five.
I could dare to dream in finding, say, one of the most famous of all trilobites - a monster at over 50 cm or more, for which only fragments have been collected, Terataspis grandis:
I'm not saying I will find one, only that it is now possible. The probability of finding one is entirely different story.
So I've now had to reassess my assumptions that have been engrained for years, and I am delighted to be wrong and to welcome yet another new species into my collection - quite a few with the season just beginning. I'll sign off with a pic of some other finds of the day: