Spent four hours yesterday at my Bois Blanc location specifically targeting Terataspis. Overall, it was a great day for it -- sunny and warm. In fact, it was the first time this season that I've had to strip down in the field as I was actually sweating, and now bringing water to digs is essential. That weighs one down, but dehydration can impair a good dig.
Let's kick it off with Deb's lovely find. A lot of it is still buried in matrix. The telltale small, rough tubercles are present, which says Terataspis.
A field shot. Likely a portion of the pygidium, thoroughly eroded. The character of these rocks make it a challenge to find nice pieces if one were to rely solely on just surface collecting. The real trick is to investigate breaks in the rock for long lines where their parts are still buried, or to find a small piece showing on the surface that continues under the matrix.
Another in the field eroded piece. It appears to be a a disarticulated series of thoracic segments, but there is some work in the lab to determine if that is the case.
An isolated pygidial spine with the characteristic barbs. There could be more, but doubtful much more. Some time in the lab cleaning it up will say.
What looks like a pitiful, junky rock may actually be covering over a nice piece here. The more obvious component with the tubercles may point to this being a glabella.
More rocks that many people might not even bother noticing. But this is the trick with these rocks: anything that has a chance to be complete will be under a few thin (but tough) layers. Since the whole trilobite is covered in tubercles, any time I see a few tubercles isolated across the surface, that suggest the possibility that it could very well turn out to be impressive.
I suspect this is showing a glabella and a right cheek. With close inspection, one can make out that the tubercles appear at a few places on the surface, again suggesting a much more complete piece underneath the matrix.
These are not small trilobites, so the rocks one brings back will not be small. Be prepared to fill a bucket very fast. In this broken rock, at the top appears to be an outline. Ventral? Eroded?
Here is a lateral view of the break in the rock, the lower piece. Note the jagged line in the middle. That is the continuation of the trilobite. This will likely be a horribly difficult prep where at some point both halves will be glued together after I determine the orientation (ventral or dorsal). The obvious question might be, "why not trim a bit in the field and separate the overlying matrix from that line?" Absolutely not. The nature of this rock does not allow for that kind of easy separation; instead, going that route will just destroy the specimen.
The trick to finding good Terry specimens in this material is to look for traces on the surface and lines on the side, taking home the most promising pieces to be worked on in the lab with a scribe, abrasion, and eons of patience. Given the high percentage of hard chert, splitting these rocks is going to yield virtually nothing but disappointment or heartbreak. Anything good will shatter right through due to the chert that comes apart in jointed blocks and not clean bedding planes.
Do I have a nearly complete specimen in the last big rock? I won't know for a while. Unlike much easier formations and lithologies, one cannot just rely on clean splits or what is obvious. With this material, you have to take chances and bring what may be promising home for further work.
Spent overnight at the Bois Blanc Formation site with a great field comrade. The focus this time was less on the arenaceous hardground, and more on the hummocky material. Although, to be fair, we were fairly systematic in our sweep. Overall, we made out pretty well, and on at least one register, pretty damn amazing. So, on to the report...
This shows the big difference between the two lithologies. On the left is a giant rugose coral in the hummocky material, and on the right is a tabulate on the arenaceous hardground.
I don't get into the habit of picking up corals, but these were small and interesting enough to find their way into my pocket.
Calymene platys occur occasionally in this material, and usually their only announcement is as an outline on the edge of the rock. In most cases, if you can see the outline, it means much of it is already worn away. The specimen at the bottom does continue into the rock, so there is hope it may be complete, even if there is almost no way of preserving that flaky shell in the process. This material can be tough and sticky at the same time.
A small Burtonops cristata that appears to be complete. I've put it under the scribe briefly, and I haven't got as far to see if the pygidium is there, but the remainder of the thorax appears to be.
And now for what was truly exciting, but may not appear so thrilling in photos. We encountered material where there seemed to be a concentration of Terataspis grandis fragments, suggestive of a moulting ground or tidal sorting. Some rocks were so filled with fragments that it was like they were just layered right on top of each other. Nothing complete, but some good parts, including a glabella.
To most people, these would just look like a big bunch of rocks with a few blackish bits, but throughout and buried in the matrix are the telltale pustular signs of the giant lichid. It will require a good deal of time and patience in the prep lab to get this up to par. The shell is flaky, but there are intervals where they are quite robust and inflated in the matrix. The evidence of them was so ridiculously abundant that we only took the best pieces home. Not many trilobite collectors can say they even have the tiniest fragment of this species, and so we were definitely spoiled. I'll post an update once I can spend some quality time in the lab with these.
UPDATE: Just a preliminary abrasion on this piece, before and after. I'm thinking this is a ventral cranidium (maybe... I have no idea). Other pieces I sampled... wow... They seem to just go on and on in the rock, which means I could get some very nice pieces once all is said and done.
And a few more works in progress:
A nice time yesterday to head out and make the 1.5 hour drive to the Bois Blanc Fm spot prospected on April 18. Less than a week later, it was essential to give the site more than a 45 minute once-over. The site itself is a good mix of a lot of Bois Blanc Fm material, including natural outcrops and the stuff ripped out of those that are in nice, tidy piles of about 5 metres high by 10 metres wide, and spanning about 60 metres long. There are also more than one outcrop, and more than one rock pile.
There are roughly two main types of strata.
The first is the wavy, bumpy, lumpy calcareous material that weathers blue-grey like Verulam Fm limestone. This material contains abundant rugose corals (some of them human arm-sized!), crinoids, platycerid gastropods (some of them real monsters), bryozoans, and broken bits of Burtonops. The calcareous stuff is only superficial, as it is just mudflows. In the meat of the rock sandwich is abundant, crystalline chert and quartz.
The second type has arenaceous surfaces that weather to expose a lot of massive coral colonies (tabulate, rugose, pipe, etc.), but underneath which are very fine-grained, mostly blank intervals. Bedding planes, where they exist, do not follow around fossils. IN other words, splitting will more than likely shatter through anything viable. This rock is very tough -- perhaps the toughest on par with Dundee Fm -- and Ludvigsen's statement of it being "perversely" so is accurate. There is no sense bashing into the harder material where the bugs are without having some evidence that something is inside -- a trace hairline, for example. Most of the rocks will split blank or with bits, and is a real time commitment.
What was odd about these rocks was the rarity of brachiopods That is not something I am used to in the Devonian. Also, these intervals had virtually no chert nodules.
If the shell had been complete on this one, it would have come home with me. This is an example of one of those giant platycerid gastropods. In this case, a very long lived one.
This one I did keep, despite missing some shell. All of these are more intact and larger than the ones I find in the Hungry Hollow Member at Arkona.
Plenty of examples of the arenaceous, sandy surfaces. And, not by far, the only or best examples either.
Not much comes out small in the lower Devonian! Anyhow, on to talk about the bugs
Anchiopsis are fairly typical inhabitants of Bois Blanc material, but they were not exactly numerous. In most cases, when they did appear in the calcareous material, there were broken and eroded almost to the point of non-recognition; on the arenaceous surfaces, they would take on the pitted, eroded appearance as seen here. I encountered bits of Burtonops and the impression of a Crassiproetus -- neither species examples I took home.
This one floored me. It is new to the collection: Calymene platys. Sadly, the top of the glabella was sheared off by forces long ago. Still, it is a substantially sized and robust specimen. It is very similar to the Moroccan Flexicalymene ouzregui, and just like Moroccan Devonian material, it is nigh impossible to split this rock without shattering through a bug. I will have to glue the head here, and then prep it a bit.
You can see how robust the bug is at the top of this picture. The skin is missing, but I collected the impression where the skin stuck. That will be a tough prep job.
Have a guess what this is. No, not a gastropod. I'll reveal its identity by the end of this blog post.
Some Calymene partials, and stuff I put in my pocket as the day went on. Those Pleurodictyum at the bottom are quite large!
Now what is this? It comes from the same mystery species as above. It is indeed most of the left genal spine of a Terataspis grandis.
The modified illustration above indicates where it would be placed. This fragment would have belonged to an individual of about 400 mm in length. Hardly the biggest (which would top out around 600 mm), but definitely a find to be proud of. This, and the other fragment, makes two examples in a day.
This has already been an incredible season, and it is still just shy of 50 days in. My checklist of Devonian trilobites is steadily filling out -- and I've still not visited Arkona yet this year. My 2020 goal of laser-focusing on Ontario trilobites has been paying off well. Now that much of the Devonian is "done," what remains are repeat visits to obtain more complete and better specimens, and to go a bit farther afield to prospect some Silurian and Ordovician spots.
I spent four hours Monday at my nearby spot with the Amherstburg and Lucas Fm material, and likely split the last remaining viable rocks in the former that could potentially have bugs. The rest is pretty much stromatoporoidal Lucas Fm trash.
A really sad split. This would have been a fairly good sized Trypaulites sp. pygidium, but it just wasn't worth taking home. And so ends what was once a very productive location. I hoovered it well, draining it of its bugs. There may be some stragglers in some of the harder, more blank material, so it will remain my site of last resort. It lasted for well over 100 visits, and it has been very kind to me in giving up 7 different species of trilobite, 3 of which were new to my collection, and 2 of those being exceptionally rare lichids, and one dalmanitid that has never been reported in Ontario rocks. I never found anything complete, but I came close twice. The Devonian in Ontario is a big tease.
I'm fairly thorough and persistent, and so can say I've emptied two honey holes in my immediate vicinity. But a new one cropped up today. I've been meaning to have a look-see at this very large location for a while. It is certainly filled with layers upon layers of sand alternating with water-worn rock that spans the lower to middle Devonian, interspersed with lots of igneous and metamorphic gumbo. At a depth of about 300-500 feet, it is steady waves of glacial backwash. You'd likely have to dig a mile to hit bedrock in this town.
Devonian formations present include Bois Blanc, Onondaga, Dundee, and even some paper shale filled with Leiorhynchus that you find in the Hungry Hollow Member in Arkona. I started finding pretty sad Eldredgeops rana bits, but that was a sign of more to come. This was only meant to be a quick recon, but this place is massive and takes a while to traverse.
To the highlights, then...
This is the only E. rana I picked up and will show here. Why, because it's a roan red rana, that's why. This appeared in some Dundee material that is just littered with tiny red brachs all the way through, like the rock is infested with fat mites. The same process of mineralization that turned them red seemed to have worked its magic on this pygidium.
This battered bug bit is not even worth focusing the camera on. If, as my field comrade Kevin says, E. rana is the cockroach of the Devonian, Pseudodechenella may be a close contender for that title. Both of these have a very long stratigraphic range. No, I didn't take this one home.
Now this is where I get excited. Dalmanitids. These are not bad at all in terms of preservation, and possibly a bit better than how they come out in the material at my secret Onondaga spot. These both came out of the same rock. In fact, all the following Anchiopsis anchiops were found in it. This was truly a good rock that seemed to be a moulting ground.
The tails come paired with heads. The one on the left is sadly just an impression. The one on the right is likely complete, and I just need to do some cleaning and light scribing to reveal it in full. I've never found a full cephalon of this species before.
More bits and pieces.
No, it is not a fossilized chihuahua head, but an impendent hypostome belonging to Anchiopsis anchiops. This is the better of the two I found. This was a great rock. If I could find a lot more of it, I would be splitting all day.
And what is that pustular bit in the centre? Likely a Coronura bit, so make that species number four at this location.
So that was a nice three hours of exploring. I do plan on going back, of course, and it's nice to add another hot spot to the prospect list. I am hopeful my new backpack comes soon as I'm not sure if my current one will hold up for another adventure. Although my tactical pack is barely a year old, it is torn in a lot of places, and the straps have had to be tied and knotted to other hoops and loops several times. It doesn't help that I carry around about 30 or so pounds of tools in it, and then add another 20 pounds of rock. The thing was bulging at the seams, threatening to burst. Not what you want to have happen in the field, far away from home.
Site knowledge: it's a Devonian buffet. There is no sense in creating a trilobite list associated with the stratigraphy because the rocks are transport erratics from all over.
In other fossil news, I have created a fantastic prospecting field document for Silurian trilobites of Ontario, and am eager to get on the road to trial its effectiveness. Obviously I won't post that here unless my goal was to ensure others would scoop up everything first. But, a few of my field comrades will hopefully benefit.
Tomorrow looks like a rainy, ice-pellety day. A good one to do a bit of prep. On Friday it is back to my secret Bois Blanc spot to do a whole day's work. Stay tuned!
Yesterday was a good day to get out and prospect, what with the nice weather and the fact that the flora hasn't grown in yet (just some budding on the underbrush). So off we went to check on a lead I got back in November, to a spot atop the Niagara escarpment. My maps indicated that the material would be Silurian in age. To my great and utter shame (or from lack of opportunity), I have yet to find any Silurian trilobites in Ontario. That being said, Silurian outcrops represent a narrow band in southwestern Ontario, with much of it being blank evaporites, anhydrites indicative of salt which is mined (yes, we have salt mines -- a perfect place to send one's children!).
The site was an abandoned quarry where the main pit was flooded some many decades ago. The exposures were apparent, and mostly around the fake lake, running the circumference (probably a good 500-750 metres) and a depth from top to waterline of about 3-5 metres. The first thing was to check each interval along the strata. Here is just a small section of the exposed stepped wall:
A lot going on. Some layers were more blocky and massive, others were thin and seemingly calcareous. But whether they were thick or thin, they were almost entirely blank with some tough, dense tiny mineralization when split. It looks a lot more promising than it actually is. Lumpy, muddy, and blank with only a few tiny brachiopods on very rare occasion, and some burrows, and pretty tough to break cleanly. But that is the Silurian for you: plenty of largely blank layers from less than ideal deposition and preservation. There are some layers in the Silurian here that are exceptional; this was not one of them!
From the sensational Silurian! This was my major haul from probing those layers. Muddy little brachs. Well, live and learn! So off we went to do a site-seeing stop.
The Devil's Punchbowl's stratigraphic range, oldest to youngest, would be Queenston Fm (upper Ordovician) to the Lockport Fm (middle Silurian). It's a conservation area, so any excavation would be quite illegal. So, it's a take photos, leave footprints visit.
Here's a nice view of the Lockport Fm that caps much of the escarpment. Both the Ancaster and Gasport Members are shown here. Buried beneath my feet would be the coveted Rochester Fm shale, home of the great Silurian trilobites. Sigh.
There are fossils in it, of course. In the ceiling of a small cavern, a nautiloid impression. Lots of nature to see, and likely a place we'll visit later in the year by hitting the paths. So off we went to hit up one more location before heading home. This time, it was an engagement in younger rocks: the lower Devonian, Bois Blanc Fm.
The photograph washes the colour out a bit, but there is the tell-tale blue chert of the Bois Blanc Fm. We arrived at the area, at which point I got out of the car and did a very quick field scan. It was not the ideal spot to start digging, so we opted to go on a bit farther to find a better outcrop with a different faunal constituency and composition ratio. Prospecting is serious work, well beyond the weekend warrior's penchant for, say, just going to fossil parks and breaking a few small rocks with a mallet!
There are layers in the Bois Blanc that are just choked with corals, forming considerable reef systems and bioherms. The rocks here are not terribly ideal for faunal diversity, and so I'm moving on...
Now here we go. Yes, there will still be corals blocking the view, but these layers are a thinner, blue-grey, highly calcareous shale that splits nice and easy. It has the same colour and consistency as the Verulam Formation, and the similar issue of not always being able to make out the fossils from the matrix when freshly split as opposed to weathered. In the shot above, what appears to be a crinoid head is rolling along with a toppled rugose coral.
Aha! Bingo. There's not much left to the trilobite pygidium here, but I have an eye for trilobitic shell material. Only the margin is preserved here with the underlying coral poking through. This was all the evidence I needed to get cracking into this layer. I knew there would be bugs, but the question remains as to what will result in the best return on investment in each layer?
A much more definitively diagnostic trilobite tail. Just as a refresher, the (work in progress) list of trilobites in the Bois Blanc include the following:
?Dalmanites comis (Hall & Clarke)
? Dalmanites phacoptyx
?[Kettneraspis] callicera [The Acidaspis of Hall & Clarke]
Pseudodechenella sp. aff. clara
Pseudodechenella sp. aff. nodosa
Note that the only phacopidae in the group is Burtonops cristata. There is a species with less microsculpture (Viaphacops pipa) that I need to add to the list here. So, let's settle the difference and call it Burtonops sp. -- At least for now. As a small sidenote, these two species were once Phacops cristata and Phacops pipa (and before that, Phacops cristatus var. pipa). Well, once all the Phacops of eastern North America were taonomically reclassified so that Phacops does not apply here as they do in Morocco, names were changed (for example, Phacops rana = Eldredgeops rana). And so these very, very similar species got split into two genera: Burtonops and Viaphacops. Confused yet?
Another Burt the Bug, this one enrolled and crushed to show the anterior/ventral side. This shale is fragile in spots, which is good to know when it comes to likely preservation (and the need to keep the field kit well-stocked in super glue). That horn-like feature to the left? Not quite sure what it is. I have some ideas that range from the banal to the wishful.
So not a bad outing at all. It began as a failed prospect and turned into something very promising. I only spent 45 minutes at this new spot, and there is a good amount of material to get through. There is some urgency, though: the spot is slated for development and will be buried under houses as soon as construction projects are given the green light to resume. It means I need to hope for the grand trifecta of time, weather, and opportunity to make the most of the spot before it is gone forever.
And this also makes the 40th day of the 2020 season. Out of three slated prospect areas, only one was viable, but batting .333 is not bad at all given that prospecting new sites usually has a success rate of about 1 out of 10. I've also encountered one other site by accident (the Onondaga stuff). So far, I've visited 6 spots total, 4 of which are viable. I haven't even been to Arkona yet this year! This is pretty good given that the borders are shut tight, and it is doubtful that our one last quarry in the Ordovician will be letting us in this spring.
Of course, this is just the first few steps into an adventure that may see me in much longer, sustained periods of prospecting, farther from home. As always, I'll keep this place updated when I can.
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 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 fenestrate bryozoans. The environment was shallow marine reef (owing to the massive presence of reef-builders).
Here is Echinolichas sp. fragment number two:
I collected the positive and the impression. It is in pretty rough shape, but any fragment of this 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:
It's not often that one can find a trove of fossils within one's vicinity-- in my case, within walking distance of my house. So time to spin a yarn and show some pictures.
There's a spot I've been returning to for going on six years now, and it has been pretty good to me in giving up its treasures. Nearly all of its material was trucked in, including rocks from the Bois Blanc, Amherstberg, and Dundee Formations. Of course, it stopped being productive by end of last year, and although it is provided me with fantastic pieces of trilobites such as Anchiopsis anchiops, Mannopgye halli, and Odontocephalus sp., among others, it's pretty much tapped out, with some areas being too overgrown now. Nothing left but splinters, mud, weeds, and dirt.
Still, I tried to give it a few more chances in the case of weathering or new material being trucked in. Nope. I've found nothing of interest there all year, so pretty much stopped going.
Nearby, however, is a different story. My new honey hole is also trucked in material -- too poor to make cement, so it is used as riprap / fill -- and there is a lot of it. Perhaps so much it may take me a very long while to tap it out.
Initially I thought it might be local Dundee Fm, and/or Lucas Fm (Anderdon Member) due to the sandy facies. Now, I think it may actually be Bois Blanc material.
So I've done about two half-days of recon and prospecting to get a handle on the site and material rather than do a systematic all-day dig. This stuff, pending rock type, can be dense, dirty, fragile, brutally hard, blank, or ridiculously fossiliferous. There are massive dome-like corals amidst smaller corals of all kinds, but in some layers bryozoans dominate.
And these are some of the medium sized ones! When I started poking around, I thought to myself that it was just a resigned end-of-visit tapping of a few boring rocks.
And then I started encountering some familiar matrix, but loaded with these rostroconch.
And then a few nautiloid/ammonoids started appearing, too. But the really exciting trip-maker that turned around my whole day, and has rekindled my interest in taking some walks outside my house is this:
Yes, a basically complete (I'll know for sure with prep) Pseudodechenella sp. Not sure of the species just as yet. Finding these, or their byrozoan/coral thicket-mate Crassiproetus, complete is far from common. After finding this proetid, I gawped at it for a good few minutes, shocked by my dumb luck! After, I started finding plenty of pygidia and other fragments. That brings me to the end of day one.
On to day two. I needed to recalibrate my expectations so as not to think full trilobites would be popping out of every rock. I was right: I did not find a full trilobite, but something no less sensational. But here's a tour of some of the other finds first.
A whole lot of sea bed goodness.
Long and branching.
This amounts to a hill of b...ryozoans.
More Crassiproetus pygidia. Not pictured yet is a fairly large one (about the size of a silver dollar for those who remember what those look like).
But enough delay. The find of the day, and perhaps the week, month, or year, would be this unattractive fragment:
UPDATE: Despite the very similar morphology, I came to the realization that this is not a Terataspis, but more likely a match with Echinolichas.
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.