Since my last post, Covid-19 has become even more serious. I've been keeping busy and getting on top of grading final papers. Of course, I also took the opportunity to get out as much as possible. So this post will be a triple update: finds, a purchase, and a drawing.
The first trip was to locate the source of my Amherstburg Fm material. We may have found it, but there were no natural outcrops. The closest was in enormous pits behind barbed wire fences and no trespassing signs -- in other words, a zero-access quarry. So, I fell back on my usual spot in search of more trilo-bits.
Some stuff I wasn't looking for. A large gastropod steinkern on the left, and a big brach and bivalve on the right.
Yes, large and very cool rostroconchs, but I'm getting a bit sick of them!
Left: looks to be part of a Trypaulites sp., and the most complete I've found. Lucky me that it stops right at the natural edge of the rock.
Right: bookend pygidia of Mystrocephala and Pseudodechenella.
And even more Mystrocephala. Preservation is pretty poor.
Lichid pygidia. The one on the left is too damaged to make out. It could be Acanthopyge or Echinolichas. The one on the right is definitely Echinolichas. I lost the positive due to the nature of this material's tendency to explode.
Hypostomes! On the left is likely an echinolichine, and the one on the right is a beat up Acanthopyge contusa on account of its shape and pustular ornamentation.
Although I was skunked on my attempt to dig through the source of my Devonian material, I at least came home to my first harpetid in the mail. Not the best preservation and prep for this Harpes perradiatus from the Devonian of Morocco, but pretty good given the price I paid.
And, as promised, a new drawing. I have about four more queued up, but they will take eons to complete as they are all ridiculously complicated... and my carpal tunnel is dogging me.
Hopefully I'll be able to get out a bit next week once the rains are done, assuming they don't put us on lockdown and home confinement. I do have some trilobite-related stuff to do around the house if that happens.
How niche a topic can I make it? Yes, today's post is about hypostomes, and more particularly, the hypostomes of lichid trilobites (of the Amherstburg Formation).
Ever since stumbling upon my Amherstburg fill area back in August, I've certainly been fortunate to crack open many a rock to find the occasional fragments of lichids, from isolated pygidia, cranidia, librigena, and even a connected thorax (just the one time, recently). and hypostomes.
The thing about hypostomes is that they are very easy to miss for a lot of collectors in the field. They don't look trilobitic to anyone who isn't already familiar with the ventral morphology of a trilobite. When I first started several years ago, I probably left dozens of them in the field. There has been much discussion and speculation on the purpose of this hard, plate that appears just underneath the cephalon, and just as much variety in morphology (check out the spooky and fierce-looking Hypodicranotus hypostome in Ludvigsen's paper here!). It is generally agreed that they served a primary purpose as part of their feeding apparatus. On that discussion, I highly recommend Hegna, T.A. (2010) The function of forks: Isotelus-type hypostomes and trilobite feeding. Lethaia, Vol. 43, pp. 411–419.
This snip of four line drawing representative lichid hypstomes is from page 188 of the lichid bible, Thomas, A.T., and Holloway D.J. (1988). Classification and Phylogeny of the Trilobite Order Lichida Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, Vol. 321, No. 1205 (Aug. 26, 1988), pp. 179-262. There are similarities among the genera's conterminant hypostomes, but also distinct differences as seen above.
At present, I have been able to reasonably identify three lichid genera from this material: Acanthopyge contusa, Echinolichas eriopis, and Echinolichas sp. cp. hispidus. These are consistent with equivalent strata in New York (see Whiteley, Kloc, and Brett's Trilobites of New York, or "TONY" among us bug enthusiasts).
Here are three hypostomes I have found since autumn of last year, with the one on the far right being a recent (as of today) find. I would guess that the first hypostome belongs to an echinolichine, whereas the middle one is unmistakably Acanthopgye contusa. The third one is still undetermined to me as of yet. It seems to share the echinolichine shape, and yet also appears to possess the granular ornamentation of the Acanthopyge. It is also by far the largest one I've found, with a width of just under 20 mm. That would possibly make the original owner between about 70-100 mm in length. Not excessively large, but not tiny. Of course, the preservation could be much better on the last two, but I take what the rock will give.
Hopefully in future posts about the lichids I can start organizing some of the other body parts, too.
Been moving tons of rock the last few days -- quite literally, in fact. I call it training for when society collapses and we're thrust into the world of Mad Max. Not quite, but it has been nice to get out and dig more. Here is a sequence of events of removing a single big rock:
Fun times! And what was in all that rock? Nothing much! Them's the breaks sometimes. The thing about this material is that you never know. It could look promising on the outside and along the visible edges, or it may be blank, but what is inside can only be determined by actually breaking into it. This rock was wide and very deep. It was also wedged and jammed in by every other rock, which in turn was wedged and jammed in by other rocks, ad infinitum. Sometimes the rock wiggles like a loose tooth, but just won't give.
So, any finds from my spot for all those many hours? I've bagged a few more lichid fragments (one of which was a real heartbreaker as it was the edge of an exquisitely preserved pygidium with all the pustules, but it started just before the edge of where the rock stopped. Argh! A number of very wee Mystrocephala stummi pygidia, the usual pygidial/genal/thoracic/cranidia assortment of Pseudodechenella sp. and Crassiproetus crassimarginatus that I'm leaving in the field. But here's something pretty:
A rostroconch (Conocardium cuneus). Rare as all git-out everywhere else but here. At this spot, I'm up to my back teeth in these things, spanning in size from a few millimetres up to 10 centimetres. Both the Amherstburg and Lucas Fm rocks at this location are well stocked with them. If nothing else could survive in the environment, or preserve well, these would.
And now for something ugly:
It's a complete Pseudodechenella sp. -- complete if we mean missing a tail and its cheeks. There's a bit more under the matrix, but not that much more. I might be able to expose the other side of the thorax at best. This one was lodged in a massive block buried several feet deep with only the top showing. Oh, and forget about reliable bedding planes. For the added challenge, it will appear on a rounded bump on the edge of the rock. Extraction was a bit nervy on this one, and it still shattered off a bit -- and that's why I carry super glue in the field for this kind of battlefield medicine.
I will likely make a few more trips to this spot even if the gains are minimal. I'm just biding time until Deb is free so we can get out collecting at a few other spots I need to check. We're also getting a new car (well, used, but a newer model with really low mileage), so it should hopefully not cack out when we're en route to somewhere like, say, Bowmanville for a dig that is now much harder to join up with these days. Losing my spot last October was really depressing.
I don't foresee any new updates this week unless I come away with something amazing. Most of the other stuff -- not pictured -- is just the same old stuff. Finding a complete trilobite in this stuff is about as likely as finding an intact strawberry in your daiquiri, such is the nature of the facies. It won't stop me trying to beat the odds of this Devonian casino in trying to find that mystical, complete lichid.
Since my MMA classes are canceled for the next few weeks, I might be able to get caught up on my trilobite drawings... I have a Damesella and a Metapolichas in the queue, but both are pustulose which equals beaucoup time to render.
More notes from the Devonian underground soon...
Well, now that it's the apocalypse, what better thing to do but avoid the drummed-up panic of the masses and go out for some bug hunting? A great thing about fossil collecting is that the chance of contracting the coronavirus from the Devonian is infinitesimally small. As my university has canceled classes in preparation to move everything online, it sees me with some free collecting time. Of course, I'll be revising my materials to be digitally migrated, and undergoing the final big wave of grading, but I may be able to sneak away a bit more often.
Today was another visit to my Amherstburg/Lucas Fm site. A lot of rock was split, almost all of it massive armour stone frustratingly rooted deep under every other rock. For all the rock split, just about none of it was of any interest to me -- just the same old, same old.
In the image above, I've already popped off the cap of this armour stone. Well, actually, it was a lot of digging, and then driving the chisel with the sledge for eons until all my bones rattled. There were a few traces of proetids amidst the usual coral clutter, brach bumpf, and bryozoan bunches. So, nothing really worth keeping. A few neat gastropods were encountered (a platycerid, and a high-spired steinkern in the chert of another rock). But the real find to make this post worthwhile...
Although a bit in rough shape, this is 2.5 cm of lichid. More importantly, is that it is a lichid with both pygidium and thoracic segments. Equally important, perhaps, is this is likely an Echinolichas sp (cf. eriopis). In Ontario. Two-thirds complete. There's a bit more hiding underneath the matrix. I doubt it will have its head, but -- who knows? I almost didn't see it as it blended right into the background matrix. To the best of my knowledge, I don't think a 2/3 complete and intact example of this species has ever been found.
Definitely a trip-maker. Got to find all the amazing lichids during the end of the world!
UPDATE: As a fellow trilobite expert pointed out to me yesterday, if it lacks the medial axial spine, then it may be a much better match with Echinolichas hispidus as opposed to E. eriopis. Here on the left is the illustration in Hall and Clarke (1888) matched with the photos of my specimen (thanks to S.M. for the stitching!), and on the right is a photo of the holotype (NYSM 4553) in Thomas and Holloway (1988).
In E. hispidus, in place of the large spine is little more than a basal bump. Of course, given the poor condition of this specimen it cannot be stated with great certainty that this belongs to one species or the other. After some light scribing to reveal more of the pygidium, I am leaving it be until I can get it in better hands to reveal more.
As it is so faint and blends with the matrix, I have experimented with different lighting as well as creating a negative in the hopes of sussing out more diagnostic details. This will be a study piece for the time being!
To recap, this is certainly rareness factor 3: firstly, a Devonian lichid in Ontario, even as a fragment, is quite rare as only two species are officially reported and confirmed in the Formosa Reef and the Bois Blanc Fm (with some questions of others having been cited by Stauffer in 1915); secondly, it is exceedingly rare to find a specimen here where it is not just an isolated pygidium or cranidium, but a pygidium with its connected thorax (those tend to disarticulate quickly); thirdly, a species not actually reported in Ontario rocks (but in corresponding NY rocks).
Image credits (and further reading):
Hall, J. and Clarke, J.M. (1888). Palaeontology VII. Containing descriptions and figures of the trilobites and other crustacea of the Oriskany, upper Helderberg, Hamilton, Portage, Chemung and Catskill Groups. Geological Survey of New York, Natural History of New York, Palaeontology: Volume 7:1-236
Thomas, A.T. and Holloway, D.J. (1988) Classification and Phylogeny of the Trilobite Order Lichida. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, Vol. 321, No. 1205 (Aug. 26, 1988), pp. 179-262
So it begins!
I still have a little over three weeks on campus, but the surprise of early spring weather means rolling in the start of the collecting season.
This year is going to be carried out a bit differently.
I'll be conducting systematic prospecting and fieldwork, which means exploring new areas and visiting long neglected sites. My fieldnotes identify several potential spots for site visits. Much of my travels will keep me focused on Ontario, and will be trained on trilobites. I have spots that span the Ordovician, Silurian, and Devonian that should hopefully result in some spectacular finds this year.
My other side goal is to continue adding to my field guide to Devonian trilobites of Ontario. To that end, I will need to explore more spots where Devonian rocks outcrop, which is not all that common in Ontario given that glacial drift is like a blanket that is about 30 - 400 feet thick in most places.
My first stop of the spring was just nearby where Amherstburg and Lucas Fm fill has captured my attention since August of last year.
On Saturday and Sunday, temperatures were hitting close to the mid-teens. Still, it takes a while longer for the snow to burn off. I set out around sunrise through the woods and to the fill area. The bonus of leaving while the temperature is still below freezing is that the mud is still frozen. It is not so great on site, however, as the rocks can be frozen together and in the ground. But that is what tools are for!
Let's dig in. Most of those rocks are rubbish. The focus is on the brownish-grey ones with bituminous streaks and lenticular coral showing. The other types of rock are generally blank or sandy/leached with mostly tiny rostroconch and crappy gastropod steinkerns. The chocolate brown rocks can be busy with bryozoans and brachs (a good sign) or muddy blanks -- you never know until you wrestle them out and try splitting them. Forget about bedding planes in many cases, or cooperative rocks that will split nicely. Some of these are brutally hard and tend to shatter. The other type of gainful rock tends to be whitish-grey and busy with well sorted smaller skeletal material. Both of these kinds of rock are reef rubble or lagoon. I don't bother with the very crumbly peritidal stuff.
A decent sized gastropod. I keep these for other people, and to record associated fauna with the trilobites.
Fairly typical fauna for this formation -- bryozoans and a few brachs. Nothing I'd take home, but anyone I take out to this spot is welcome to them.
Some pretty unremarkable lichid fragments (top two, and the lower left). I keep them for completion's sake, and lichids are generally rare anyway, and that includes fragments. The lower right is likely a Mystrocephala stummi. They are very tiny (0.3-0.7 cm wide) and quite easy to miss.
More lichid frags...
Plenty of Crassiproetus pygidia, and this platycerid.
Not that I want to jinx anything, but it looks like we have a few weeks of mild weather to look forward to, with possibly Sunday my first post-winter return to the field. It will be another engagement with the Amherstburg Fm material, but I have been quietly developing plans for new prospects.
In trilobite news, with the very recent publication of Bignon et al.'s paper, there are now 14 Orders of trilobites:
Agnostida SALTER 1864
Asaphida SALTER 1864
Aulacopleurida ADRAIN 2011
Corynexochida KOBAYASHI 1934
Eodiscida KOBAYASHI 1939
Harpetida WHITTINGTON 1959
Lichida MOORE 1959
Odontopleurida WHITTINGTON 1959
Olenida ADRAIN 2011
Phacopida SALTER 1864
Proetida FORTEY & OWENS 1975
Ptychopariida SWINNERTON 1915
Redlichiida RICHTER 1932
Trinucleida BIGNON et al 2020**
The Trinucleida were once a superfamily in the Asaphida, but have now been elevated to full Order status. And, to be honest, comparing the appearance of Trinucleids and Asaphids, they seemed an odd match insofar as they appear to differ more than they appear similar. All that being said, I'll need to revise my trilobite gallery to reflect this (and about three other Orders I've been too absent-minded to add) -- something for a rainy day. For now, another drawing:
I also experimented with some mid-tone paper, but just a really quick sketch:
So that one is just a draft for now, flagged for redoing it properly.
And this Moroccan phacopid came in the mail. I actually did not have an example of Zlichovaspis rugosa, and the price was too good to pass up. The quick snap of the bug hardly does it justice in terms of its impressive size. This is not a premium prepared bug -- visible scribe marks and a coating to hide a few mistakes is pretty customary for a B-grade bug, but even those can command high prices. In this case, I got it for a very good deal.
I am just more excited at the moment about getting back out into the field. The snows are quickly receding. I've been digging into Stauffer's 1915 text on the section featuring the Amherstburg/Onandaga material, which seems to be the most comprehensive I've seen in terms of a faunal list (albeit a number of those taxonomic designations have been revised significantly!). And, with just four more weeks of classes, serious field time cometh! Hopefully I'll make out okay this Sunday to post some finds. Until then...
Tomorrow is back to work (or, 87 days until the end of the semester). I'm getting an early start on the season, mixed with post-season activities. On January 3rd, I spent about four hours out at my spot reducing bigger blocks into smaller ones. Not much at all was found that I was going to bring home, and certainly no lichid fragments save for one that was simply not worth it. But, at least I was out there before the snows came.
I didn't take more than a photo of this one as an interesting an illustrative example of a bedding plane with a sponge. Looking more closely, there are at least three rostroconch in the mix, a few trilobite pieces, a rugose coral, and maybe a few brachs. This photo was more about the bumpy sponge, however.
I got in the lab a few days ago as well to prep this trio of Eldredgeops rana rollers from the Arkona mudshale. I mostly relied on abrasion. This stuff cracks as it dries, so I needed to stabilize a few spots with cyanoacrylate. The bugs in this stuff are generally smaller than those at Penn Dixie, and those that are approaching that size are usually very poorly preserved. In this case, these are near Penn Dixie proportions, and just a little bit crushed. Their delicate, flaky nature in the Arkona meant that I had to leave some of the matrix in place -- and particularly where they crush leaving a kind of sharp crest rather than a rounded area. In the process, an eye flew off the bottom ventral, but I miraculously retrieved it from the blast box debris and glued it back on.
A good fossil friend of mine recently purchased a large lot of unprepared Moroccan bugs from the Devonian layers of Jbel Mrakib. He was kind to peel me off four of the easier pieces (mostly phacopids and proetids -- nothing with ridiculously complicated spines). This will be practice for me, and my first Moroccan bugs for preparation. The matrix is much harder than anything from my collecting areas, but the CP can get through it. My first go is not going terribly well, but I'll keep at it. These are all common bugs, so I expect to ruin a few as I learn. The question will be if my tools are up to the job.
And yesterday I completed a drawing I had barely started a week before going to Jamaica.
So, that makes three out of five regular fossil-related activities to kick off 2020: collecting, preparation, and illustration. Hopefully it won't be long until a few new articles come my way so that I can fulfill the research portion as something to make the daily work commute on the bus more tolerable. The fifth activity is to continue some remote prospecting work to identify more potential sites for 2020. So far, I have about five locations, two of which span larger areas that may contain multiple outcrops. There are also a few must-revisit locations, too. Just 87 more days until collecting and in-person prospecting can be added again to the mix.
It is still rather remarkable that I'm able to get out for fossil adventures this late in the year, although there is no doubt that winter will have its final say in the days to come, possibly as soon as New Year's Eve.
On December 27, myself and two other collecting comrades made our way to another part of the Devonian of Ontario for an all-day dig event at an undisclosed location. The focus may have been on crinoids, but other stuff came out, too.
Preservation can be a bit iffy on this material, but here is a crinoid terminating at the top with a calyx and its attendant spinplatycerid. It will look a lot nicer once I get it in the prep lab.
A collection of calyxes, still dusty from the field. The one near the bottom still has some of its arms showing. These should all prep out nicely.
A calyx parked between an interesting plant fragment above, and crinoid arms below.
Closeup of the underside of a calyx showing the stem/cup attachment.
A real oddball we found. This is plant material, but note the fascinating barbs.
Trilobites, too, although they tend to show up rather small in this layer (larger ones are quite flaky and do not preserve well). A trio of Eldredgeops rana rollers on the left, and a mini roller on the right (a few millimetres wide!).
In all, a good outing and everyone came away with something. But today (December 28), it is back to my spot for another go at the Amherstburg material in search of more lichids and the dim hope of a complete proetid before the snows be a-blowin'. I'll update this post later with whatever I may find if I don't strike out.
Managed to spend two more days at my site. No major fireworks to close out the collecting season, which I officially put to bed on December 30th, 2019. I'm mostly left with second- and third-best rocks at this point that tend to be harder and more often blank or small bits. Still somewhat productive, though.
An Echinolichas in pretty poor shape. I found another similar one the day before that was in even worse condition. That being said, it pays to split the harder/blanker intervals as this lichid likes to appear alone.
Bit of a blurry shot since I was too lazy to bring out the Olympus, but it is likely another tiny Mystrocephala stummi.
I picked these up because they were interesting. The first is a completely chert-ified rugose coral slice, and the second is a monster Strophodonta brachiopod.
It is always sad to bid farewell to a collecting season, but there are a few things I won't miss... The brutally tough stone, the bullet-like shards that strike my shins and face, the tedious process of having to unlock rock that stubbornly holds on even if it wiggles, the endless parade of corals and rostroconchs.
And I've already dipped into post-season activities in spending a few hours in the prep lab and getting back to drawing and research. This blog will not be left in winter silence!
"Yes, this was the last day... I mean it this time!" -- Given the number of times I called an end to the 2019 fossil season (November 1st, 20th, and 26th), I seem to have embodied the postmodernist novel's unreliable narrator.
But when the temperatures are going above freezing, and there is little to no snow on the ground, why would I wait until spring? As the winter forecast is calling for brutal snowstorms, the polar vortex, and likely a long delay for spring, getting out there whenever the conditions are lined up makes complete sense. This is the unexpected surprise opportunity after returning from Jamaica.
These are the shortest days of the year, so I had to wait until about 8 am for the sun to rise, and then another hour for it to warm things up a bit. When I reached my Amherstburg Fm site, the ground was still frozen (including some of the rocks), with some snow and ice. But after a few hours the temperature soared to about 6 Celsius(!), but not warm enough to melt the snow in the rocks' shadows.
It was not the trip of all trips, but I did okay for this being late December.
This was first blood: a Crassiproetus crassimarginatus pygidium. This, and several other proetid pygidia, I left in the field since it would have taken too much effort to reduce the matrix just for these. And, like most trips, this was the rock that would pay out while subsequent rocks would be largely duds.
More "leave 'em in the field" specimens, mostly of the large brachiopod, Strophodonta. How big? The largest of the bunch has a width of about 3+ inches (~7.5 cm).
The nice articulation of this rostroconch (Conocardium cuneus) persuaded me to bring it home.
The tripmaker was also a heartbreaker. Pictured here is an Acanthopyge contusa pygidium, but with very nicely defined pygidial spines. Sadly, it's an impression that I noticed some time after I had been steadily reducing the bloc, and my search for the positive was to no avail -- likely lost to flying hammer blows or as a chip fallen through the cracks. I also found an actual positive of another example, but the preservation is so poor that I can't bring myself to post it here.
But it isn't over yet. Today promises to reach 8 degrees celsius, full sun, so I'll be returning. This post will be updated later.
Another not so productive day; plenty of rock split, but nothing much to show for it. A good chunk of time is spent searching for the right rocks. The fossiliferous ones with trilobites are very hard to find amid the usual blank, sparse, or complete blanks. I thought I would dedicate this portion to the process.
Scouting the right rock requires a bit of eyeballing of the outside to determine what sort of fauna (if any) would be on the inside. I also go by colour and texture, so if it is grey-white, tan, or brown, then I might go to town. Those rocks that have these features but appear blank on the outside or with too many tightly packed black wispy mineralization lines are generally either blank, filled with mineralization trails with the occasional small rostroconch or coral, or just sandy matrix supported colonial coral tubes with nothing else. If the matrix grain is too large (like sand), it is unlikely to support much else but coral and small brachs. If the rock is too fissile, it is usually also too bituminous and contains a few toppled corals and mostly dimpled stromatoporoids -- which is an indication that I'm too high up at the cap of the reef, which may have been subaerial or at least far too high energy for anything but the sturdiest to settle.
Finding a rock that meets the criteria of colour, texture, and promising vertical appearance does not guarantee that the interior will be a "trilobonanza" either. Some of these may contain just shredded bryozoans and a few small brachs, amid some toppled and broken rugose corals. When seeing that, I know the deposition conditions were far too sediment-worked and high energy to support trilobites. They may also be incredibly dense so that there is no chance of hitting a bedding plane. And by dense, I mean even harder to split than they already are. That stuff breaks in fractured, conchoidal chunks wherever the rock is weakest. Not good.
Once I come upon one of those rare rocks that seem to meet my criteria from experience with this material, I spot check the top and bottom where possible to get a sense of what "chapter" I am in the story. I know, for instance, that a top portion containing large horn coral means I have to split down a few inches below it. After that, I may also see if I can cleave a piece vertically or work my way down that way to pinpoint the busy bedding planes.
One indication that shows promise is in finding larger fauna, such as big brachiopods and intact fenestellate bryozoans. Of course, if the plane is busy in general, that can be an indication, but again not always: at times it is busy with just tiny fragments. Or filled with vermiculating tube coral. Or just branching bryozoans.
If the rock has even a single trilobite fragment showing, such as a free cheek, a genal spine, or a pygidium, it is marked for excavation and splitting. Again, there are no guarantees that the rest of the rock will be as generous.
This is an example of the process. I've wrestled even larger, armour stones, from these piles, so this is not the most challenging example:
As this rock showed some promise, I cleared away some of the overlying rock to the upper left so as to have a closer look at its layers. Compounding the difficulty was that this was early morning, and the mud is frozen, as are some of even the smaller rocks that need to be tapped with the hammer before removing. In this image, I've already done some exploratory slicing of the top and was intrigued with what I was seeing enough to continue.
Clearing away more debris around the rock. At this point, I'm unsure just how deep this runs. The small pry bar is not budging this, and I usually stop trying when the bar starts bending. What I would learn later is that this rock was running under the even larger rock to the upper right. Sometimes it is a game of unlocking rocks whereby you need to unlock the rock by removing those around it, but then you find those other rocks are also locked in by other rocks, and so on. I try to limit those instances as sometimes it seems never-ending, and I will encounter a rock that weighs over 600 pounds that I just can't budge.
By this point, it has been nearly an hour. I've done some exploratory chiseling, but the rock is too thick and dense to get clean slices. Instead, it tends to fracture upwards, which is useless as it creates rounded concavities that make splitting impossible. So why not use the sledge and swing it against the exposed upper left? No dice. All that smashing achieves is a mashing and denting. How about a chisel? Can't go too deep down on this as I'll just end up driving the chisel in about an inch and creating tons of powder and no break. What about coming from the lower right? A sensible approach...but this is a game of angles at times and what this picture does not show well is that the rocks on the lower right are on an incline while the main rock is on a slight inverted incline, which means the chisel won't go in straight.
When all else fails, and no measure of even the most awkward angles of hammer and chisel will work, or pry bar will budge for clean extraction, it is time for brute force. In this case, I exploit any visible weakness in the rock and go for a vertical split. It's not ideal as it might cleave through fossils, but sometimes you need to break eggs to make an omelette. Having exposed a chert area with a hairline fracture, in goes the chisel and down comes the sledge hammer. It isn't a big chunk, but it may help going forward. This is the beginning of the momentum in removing this one. Sometimes those cracks are superficial, and sometimes I have to repeat this chunk-split approach a few times if the rock is even larger than this one.
Hundreds of hammer blows later and some artful chisel-action, I'm able to split the top off this one. The pry bar was needed to remove it as it was partially stuck under the bigger rock, and that meant gradual push/pull in a game of inches to slide and wrestle it off. That leaves just the lower half, which is still deeply lodged in the dirt and debris.
Inspection time. Let's have a look at the upper portion. Apart from a big brach and a few big bryozoan pieces from about an hour earlier when slicing the uppermost part, this seems to have a bit of promise. I set it aside for splitting later.
Both pieces are out! The one on the left is actually quite thick (about a foot on its widest edge). A Crassiproetus pygidium is showing at the top of this one, and you can make out its impression on the rock right next to it. I'll still need the sledge to split these into more manageable pieces for the rock hammer. From observation, I note that this entire rock has just two active bedding planes. Sometimes even the bigger rocks may only have one thin plane, and these are very tightly packed. The rest of the layers tend to be sparse, broken bits or entirely blank.
So, the result of about 90 minutes of hard work and frustration? A 3 mm wide pygidium of what I suspect to be Mystrocephala. Yes, all that work and splitting for a 3 mm fragment. If I specialized in collecting non-trilobite fossils, this rock would have been more gainful. As disappointing as the ROI is on this bloc, at least it was something! Other instances have led to zip, or sometimes the rock that just keeps on giving. There's never really much certainty until you excavate and split them.
Six hours of scouting and pounding through mostly blanks and bits didn't net me much more today other than this fragment of an Acanthopyge pygidium, with some kind bryozoanal growth on its left side. I've had better days! But, the viable rocks are getting much harder to come by, and I'm having to default to the B- and C-piles.
I'm not going to say the season is done yet. There looks to be a few more good days in the forecast for one more go. I've marked two so-so potential blocs for splitting that I'll get to first so as to save time on scouting.
Xmas Eve: Totally skunked. It seemed what few potentially viable rocks I could find were just loaded with corals and uninteresting fragments, so I came home with nothing despite putting in a good six hours. I had queued up a few larger rocks two days earlier for splitting, but those were a bust. However, no sense in complaining, and this might have been only the second or third time I've ever come back with absolutely nothing to show for the effort.
Boxing Day: A much better outing than the last one. Although I can't say I came back swimming in riches, I did have much more luck.
On the left is the impression of another Echinolichas eriopis. The positive side is only one half of the pygidium, and seems resistant to good photography which would otherwise show its nice pygidial rib annulations. On the right is a lichid genal spine / free cheek that is still attached to the glabella (which itself is under a bit of matrix for me to remove). This would be a first in finding an attached cheek to this lichid (possibly Acanthopyge, but I'll have to uncover the glabella to be certain).
The new trick is not to turn my nose up at a certain B-pile type of rock that is largely blank, but of the right strata (not grey, but the light tan colour). What is blank can quite surprisingly display a sudden busy layer, but it is not obvious when reading the rock's vertical record. It means persistent trial and error splitting. I've now queued up over ten metric tons of this type material for my next return, which likely won't be until tomorrow (Saturday, December 28) as I'm due to hang out with some of my fossil buddies on a trip to Arkona today.
So just when I come to desperation (yet again) that I've exhausted my site's possibilities, a bit of itinerant, exploratory splitting has opened up new possibilities. Granted, the rock is perversely dense, frustrating in many places, and some of the rocks marked for breaking down are the size of a trunk, but I'm nothing if not determined.
I'll likely have tomorrow and Monday to get at them in search of more lichids. After that, it is likely that winter will bury and freeze all hunting trips until spring. Still, this welcome and unexpected extension of the season means I have to make the most of it!
Today was a gorgeous day, and it is somewhat fitting that the last day of the collecting season be sunny and warm. Yes, this was the last day... I mean it this time! As there are only 11 days left until vacation, a mountain of essays to read and grade, and the fact that winter weather is going to return and stay in earnest, today was it.
The rocks were heavy and hard as always. I didn't come away with as much material as some of them were absolute duds. Like last time, most of the gains were made from a single rock. Let's lead off with the usual suspects:
Left: I think I found this one on a previous trip, but it was in my bag when I was emptying it. Likely a Mystrocephala stummi with mineralized goop on the posterior border of the shell. Right: the ever-present and readily available Crassiproetus crassimarginatus. I am impressed with just how large these ones can get in this material.
There were plenty of Pseudodechenella pygidia (and free cheeks galore), but all of them were on the small side and situated in the middle of larger rocks, so not really worth the effort to reduce and bring home.
When tubercles are showing, that means lichids are in the house. I'll need to clean this one up.
I also found (not pictured) the thorax of a Pseudodechenella that needs to be glued, and a very well defined cranidial fragment (median lobe) with exquisitely detailed tubercles.
This one is pretty tricky to photograph as it seems that my devices try to overly blend the specimen and its matrix. The left is the positive, which still has some parts concealed under matrix. On the right is the negative. Yes, another candidate for Echinolichas eriopis.
A few more attempts to photograph the positive from different lighting angles. What are the chances of finding a new lichid twice in as many days? This one is as large as the one I found Sunday. Whereas the former one has a bit better detail on the pygidial ribs, this one has evident pygidial spines (with tubercles!). There is still an opportunity to reveal more on the right side.
It was nice to end the season on a high note. Although I never quite seemed to find an absolute complete trilobite in this material, these last three months have been filled with surprises. Trilobites in the Amherstburg are very much a faunal minority compared to the thickets of coral and bryozoans, but I made out okay for the effort. The site will now be waiting for me in spring.
Down tools. For real this time!
At this point, I'm just about ready to summarize some key findings, pulled from my field notes, about this imported material. As stated in previous posts, it is reasonable to assume judging by the lithology and presented fauna that this is material from the Amherstburg/Lucas Fms. The nearest and cheapest source of this material for the purposes of a drainage area riprap would likely trace this material to a quarry or quarries in Ingersoll. As it is unsuitable material for cement, this material is generally stripped off.
The fauna is suggestive of a minor reef community. Apart from the thickets of toppled rugose coral (likely due to wave action) and some colonial rugose as well as tabulate (Favosites) communities that have considerable in-fill suggestive of rapid sedimentation burial, the common presence of bryozoans as binders does point to reef development. Bafflers such as crinoids are more scarce in these sediments, possibly suggesting a lack of cohesion and maturity of these minor reef complexes. In some of the materials, thin black layers may suggest a shallowing sequence and possible subaerial exposure in shallow, possibly peritidal conditions. Deeper waters are reflected by the appearance of some packstone pulses with larger grain-size limestones. The upper portion of the material with black stained shale partings or a higher appearance of chert nodules (indicative of siliceous sponges) may contain stromatoporoids, branching bryozoans, and rostroconchs (?Conocardium cuneus). Likely presence of algal mats.
What is known is that this environment would have been situated in the Appalachian basin, southeast of the Findlay arch (by current orientation). It is not unreasonable to expect shared faunal elements with equivalent strata found in New York, such as the Onandaga Fm, and more particularly with the Edgecliff, Nedrow, and possibly Moorehouse Members.
Trilobite fauna are generally represented as a minority fauna in these relatively small coral bioherms. When present, disarticulated moults are suggestive of higher energy conditions, likely swept into gaps and pockets in the biohermal mass. Of note is the complete absence of phacopids, suggesting the environment was not well suited for their spread into this particular biohermal region. Instead, burrowing proetids are relatively abundant, including the illaenimorph Crassiproetus crassimarginatus that appears most commonly in these sediments, followed by Pseudodechenella sp..
Here is a comparative table of trilobites of equivalent geologic age appearing in three locations. A-SITE = the area under study; A-ON-FR = Formosa Reef, Ontario (Michigan basin); O-NY = Onandaga of New York.
As is evident from the table above, only two species of trilobite are shared between the three locations. My location shares three trilobite species from the Formosa Reef, and five with equivalent strata of New York. Two species (in bold) are shared across all three strata.