VIsit to Little Wern (ID requests?)

[joeedwardmorris]

Hi, been obsessively into natural history generally and evolution / prehistoric life particularly for ever, and this year decided to try and collect some fossils for the first time since childhood. My wife found Little Wern online and we visited last weekend, the owner mentioned Joe Botting as the man who put the are on the map paleontologically and that led me here. What an amazing location it was! I was basically hoping to take home a handful of complete trilobites, which I did (all Ogyginus corndensis from what I can tell?) but it slowly dawned on my amateur sensibilities as I hacked away at this priceless remnant of ancient sea floor that this site had more to it - the productive layer was full of strange looking films and shapes that looked as though they may be of interest to a more educated eye. I felt somewhat uneasy smashing into this fragile record with a hammer and chisel, and can't help but feel this site should be a bit more protected!

I'd love an expert opinion on the ID of some of the stuff I found (and indeed whether some of them are fossils at all).

Here's a few I thought looked interesting, all from a couple of cubic feet of rock... (excuse iPhone photography, would like to get my wife's macro lens out and do some proper ones when time allows!)


Was wondering if this small (approx 8mm) object with visible segments could be a crustacean of some sort (phyllocarid?)


This looks organic (almost like some kind of curled up worm) but wasn't sure if it is just a geological feature

This looked almost like a cross section of sponge or coral, with its spotted pattern of 'holes'

This looks like a tiny bivalve, about 7-8mm across.

Was wondering if this was a stalk or holdfast of some bottom-living organism. It came out of the surrounding mudstone very cleanly leaving a clear mould.

I'm guessing this is the head of a small trinucleid trilobite. Could the body be buried in the shale and revealed carefully somehow?

IS this the internal mould of a brachiopod? There were lots of these.



Lots more stuff too but don't want to bombard the place on my first post!
Anyway, absolutely loved it and would love to get involved in helping out on a proper scientific dig in some way one day!

[Joe Botting]

Hi Joe, and welcome! It's good to see some more stuff from Little Wern - we keep meaning to go back there, but never seem to make it! Glad you enjoyed your visit, though.

As you say, there are lots of interesting things in addition to the trilobites. We know, for example, that there are palaeoscolecid worms, graptolites, various molluscs and sponges. There are also some very uncertain blobs that might not be anything... as you know all too well!

So, I'll go through them in sequence. By the way, it's handy to number images in future posts, to make it easier to refer to.
1. Not sure. Could be a fragment of an Ogyginus (the centre of the 'head'), partly exposed and partly broken.
2. I wish this was a sponge... but it's not, despite an uncanny resemblance to some we were recently colecting in China. It's on a very weathered surface with lots of iron oxides, and I think it's a radial array of limonite crystals around what might have been a pyrite blob in the centre. Would probably have to see the specimen to be sure, unfortunately (let us know if you're ever in Llandrindod!), and if it is a sponge then it would be a very impressive one... but I really don't think so.
3. Again, it's a very weathered surface with an oxide crust; it seems to be just some mineral textures that precipitated inside fracture planes in the rock. However, there might be more visible in person!
4. That does indeed look like a little bivalve, and they are around (and quite diverse) at this time in the Builth Inlier. It's extremley symmetrical, though, which is making me wonder about some sort of brachiopod that I've never seen... but yes, on balance most likely a bivalve. I'm wondering about a nuculoid of some sort, perhaps along the lines of Deceptrix. It would probably be a new species, but can't be described without the details of the 'teeth' along the hinge!
5. That's an orthocone (straight-shelled) nautiloid - an ancestor of the modern Nautilus. Quite common predators, but certainly not abundant at Little Wern.
6. Yes, indeed - Bettonia chamberlaini, to be precise. This will have come from the main part of the quarry, as it seems to be replaced by Trinucleus abruptus in the upper 3 m or so.
7. That's an Ogyginus corndensis cranidium: the main plate in the front part of the animal (not really a head!), with the stomach region under the bulbous central bit. When they moult or die/decay the plates separate and these pieces are by far the most common remains.

Keep 'em coming!

[joeedwardmorris]

Wow, thanks for the quick reply. What an amazing age we live in which it is possible to get specimens checked out by a supremely knowledgeable expert at the drop of a hat. What I would have given for such a possibility when I was young.

Well, a mixed bag then. i thought it likely that some of these would be purely mineral phenomena, but just dont have the knowledge and you never know when it could be something a lot mpre interesting. I'd love to get a lot better at teasing out the many nuances of this kind of thing.

Id like to go back to the area in the not too distant future so maybe Ill get a chance to show you the 'pseudosponge' in person to double-check. It came out of the middle of a harder nodule I split in half. Quite an interesting looking thing, even if it isnt a fossil!

Very pleased to have picked up a chunk of nautiloid on my first trip out though! Ive been fascinated by those ever since seeing the paleozoic sea floor reconstructions in my old books as a kid.

Also happy to have unwittingly picked up a trinucleid which I didnt recognise until I got it home. Id been looking for one at upper gilwern to no avail (though got some nice Ogyginus).

Interesting about the bivalves. So is the preservation just not complete enough at this site to fully describe them?

Good to know that last one is a cranidia - that makes a lot of sense now i look at it again, I think I got the brachiopod idea from misreading something elsewhere. I wondered why we found a lot of tails but no 'heads' - were the outer bits of the cephalon more prone to decomposition or disintegration then? Or just less noticeable?

Will stick up a few more pics soon when I get a chance.

[Joe Botting]

I'm always amazed at being able to exchange images and files with people on other continents... it is an extraordinary world we live in right now. I'm really not sure about the 'supremely knowledgeable' bit, though... we're all human, you know!

Yes, it's a pretty good haul, for the first batch. Aside from the oddities like worms and sponges, Litle Wern isn't all that diverse - just the three trilobites, a couple of graptolites, a few brachies and molluscs... it's quite an interestingly depauperate fauna, in some ways. And then you get the palaeoscolecids, which are the most diverse assemblage known from the UK, and from most of the rest of the world too, for that matter.

I don't honestly understand the ecology of the place just yet, but there are a few similarities to some other localities we're working on. In particular, we have a small quarry from higher in the sequence (just after the main volcanic interval) that has similarly low diversity of most things, and then an extra thirty or forty sponge species! Neither site seems to have any echinoderms, which is a real novelty in this area - no mitrates, and no crinoids. Probably this means they're in the same water depth interval, between the crinoid-dominated shallows and carpoid-dominated deeps. There are similarities in the sponge faunas that suggest environmental similarity as well...

When you start to really try to get to grips with what was going on in an ecosystem, it can be incredibly satisfying... and frustrating.

Yes, the bivalve (assuming it's not a brach - I'm not 100% sure) would need fine preservation of the hinge area. No reason for it not to be found here, though; it just doesn't seem like that specimen has got the right detail. Ideally you'd want a suite of several specimens, showing the hinge, muscle scars, and so on, before a specialist would take it on for description... so keep an eye open for more!

For the trilobites, the anterior lateral bits are called the free cheeks (librigenae), and are separated from the cranidium by a suture. This is designed to separate so that they can moult, and the free cheeks are the first bits to be dropped. Most 'complete' trilobites lack the librigenae, and are actually complete moults; if you have a complete one with the cheeks in place, then it's a carcass that was probably buried very rapidly (before scavengers had a chance to attack it). In fact, there's a high chance it was killed by the burial event.

Anyhow, looking forward to the next installment.

[joeedwardmorris]

All very interesting stuff Joe, thanks.
Spent a couple of hours at Upper Gilwern too, all just Ogyginus I think but got a few nice specimens from one little outcrop.
No scientific interest I'm sure but nice to have! Here's a quick selection just for anyone's interest!



I wasn't sure what 5 and 6 were but from what you said I'm guessing they are just Ogyginus bits!
For fossils like number 3 is it possible to expose the rest of the specimen? I love the colours from this site.

[Joe Botting]

Nice! Gilwern is really famous mainly for the Ogyginus, of course, but a lot more has come out over the years... various other trilobites, crinoids, starfish, sponges, monoplacophorans, bryozoans, bits of large unmineralised arthropods (possibly eurypterids?)... it's a fascinating place, but the scarce species really are very scarce indeed.

These are all Ogyginus, as you suspected (although there are two species at Gilwern: the common O. corndensis with 6-8 pygidial lateral ribs, and O. intermedius with 9-10). Number 6 is an isolated free cheek (compare with the one still attached in no. 3), whereas 5 is more complicated... it seems to be the underside view of possibly a complete one that is still in the rock. You've got the doublure (the folded-over margin over the front of the 'head'), and the hypostome in the middle - a plate which covered the mouth area. You can see the impression of the hypostome in 3 as well, compressed into the glabella (the bulbous bit in the middle of the cranidium... I know, so many anatomical terms!).

I'm sure that 3 can be prepped, but it's quite a skilled job, especially in this rock. Ideally you want a little pneumatic engravers' pen (hammer action rather than rotary), and a little microscope to work under; it's too hard to use needles very easily... although you might get somewhere with a pencil sharpener blade, it's very easy to make a horrible mistake!

[joeedwardmorris]

OK last couple of sets before I bore you to tears with common bits and minerals
Here are most of the remaining odds and ends, and from our discussions I suspect most are either bits of Ogyginus or nothing at all, but you never know I guess!



1 - Thought this could have been a trace fossil, it came out in two halves like a tunnel through the mud and has some hints of annulation perhaps (could be nothing of course).

2 & 3 - Graptolites? Am I right in thinking these would have been present in the surface water far above as plankton and drifted down when they died?

4 - looks like a ring of small bumps with another in the centre. Probably nothing!

5 - This looked organic to me. Could it be a brachiopod? Or just another trilo-bit...

6 - I found a few elliptical nodules like this, Im presuming they are just a mineral deposit but because there were a few so similar that there might be more to it.

7 - Thought these linear traces could be something, but again most likely a trilo-bit or nothing.

8 - Just another close-up of the fake sponge because I like it!

9, 10 & 11 - Trilobite segments?

12A/B - These are just to show the different sizes of a kind of strange semicircular nodule structure that I found a couple of in very similar sizes and shapes, both with a cranidium in the centre (only retained one unfortunately). Is this just an artifact of how sediment has accumulated around the fossil? Also I noticed the thin orange lines that can be seen outlining the nodule in 12A running through the rock in different outline shapes in many places. What causes this?

Thanks again for your patience and fascinating info here!

[joeedwardmorris]

And finally a selection of Ogyginus from the same couple of cubic feet of rock, just for posterity...
I'm presuming the predominance of these is partly due to preservation bias, but I imagine they must have nonetheless been very abundant. Is there much inferred about their life histories? Why were they so successful in this habitat? Were they scavengers / filter feeders? For such a common species I can't find a great deal about them

[Joe Botting]

Sorry, been really busy for the past few days! Thanks for the neatly-organised array, so let's see what we've got...

1. Looks more likely nautiloid, but hard to be sure without a closer look.
2, 3. Yep, Didymograptus artus, the most common graptolite in these beds. As you say, these were planktonic colonies, and would have sunk after the animals died.
4. Probably just a cluster of little concretions that have weathered.
5. Could be a little brachie, but there don't seem to be any radiating ribs, which would be unusual. Bivalve is another option, but I can't see enough detail... a close-up might help.
6. Not seen these... it seems to be a very weathered fracture plane, so my guess from the image would be spheroidal weathering surfaces that intersect the bedding planes to produce an elliptical outline.
7. Definitely trilo-bit... looks like one librigena at left, and some other indistinct gubbins. Ogyginus, as usual.
8.Cute... but still can't really be a sponge!
9. Ogyginus partial thoracic rib: axis to right, lateral part to left, opposite side missing.
10, 11. Faint, but trilobite fragments, as you say. Probably a librigena (10) and a pygidium (11), but hard to be sure!
12. Not so much a concretion/nodule, but rather a weathering effect. The water seeps in from fracture surfaces and the exterior of the outcrop, and this often results in concentric weathering horizons eating into the rock, usually along smoothly curved surfaces. It's very common in shales close to the soil, but if you were to get a few metres further down, they'd disappear. There are concretions there, but those are really hard, and very obviously distinct from the surrounding rock. Yours appear to be just odd shapes resulting from these weathering effects.
You'll often see fossil pieces in the centre of these planes, because there was some pyritisation. When pyrite oxidises it increasing in volume, splitting the rock apart. The yellow lines are part of this process: water percolates down the crack, and deposits iron oxides like a tide line within the fractures. Similar colour rings penetrating the whole rock are also quite common, especially in porous sandstones.

As for the Ogyginus, that's a very nice selection! There is a bias that multiplies the number of trilobites, but this should have acted almost equally on the other species too... and yet this is the most common trilobite in the area at this age, by a mile (except for a few isolated occurrences where trinucleids dominate). Ogyginus corndensis appears to have been a true generalist, in a way that we rarely see... it was everywhere! We've found it in shallow-marine, near-intertidal environments, and in the deepest mudstones in the area (just before it finally went extinct). In almost every case, it's the most abundant trilobite there. Whatever it was doing, it wasn't half good at it..!
Interpreting their ecology is quite tricky because we have little to go on; it doesn't have any really distinctive features, and was probably a scavenger and detritivore, rather than anything very specialised. We've found a couple inside a nautiloid shell, which is an occasional feature of trilobites; probably, this was nesting behaviour. We also get clusters of juveniles, probably sheltering beneath some unpreserved organic matter in order to moult in safety. So, they seem to have been quite gregarious. Best guess is that they were jack-of-all-trades, and could make use of virtually any food source they could find.
When we get exceptional preservation, or start counting fossils rigorously (taking account of multiple moults, etc.), they're not quite as abundant as they first appear, and usually it's another group that was actually dominating - sponges, for example, or little brachiopods. In the case of Little Wern, the preservation isn't quite good enough to be sure, but it's quite possible that trilobites were outnumbered there by palaeoscolecid worms!

Ta-ra the noo,
joe

[joeedwardmorris]

Thanks for all the fascinating info, Joe.
Looking forward to my next trip to the area already!