Post by Joe Botting on Oct 6, 2014 18:38:02 GMT -5
Speaking of ophiocistioids (following Tarquin's Carboniferous goniodont), here's a fossil that is --allegedly-- another one. We went with the fossil club to a Silurian (Ludlow) graptolite quarry called The Pales, in the vain hope of finding some of the extremely rare pseudoplanktic crinoids that are rumoured to lurk therein. We found lots of other things, but only a few ossicles of crinoid - not enough to do anything with.
As usual, though, something else turned up instead. Here it is.
It doesn't look like much, and is only about 3 mm long, but the ring of plates making an undulating margin, combined with the large, irregular plating and no stem or arms, suggests a thing called Volchovia. To check that, we'd really want more specimens, and some of them showing the periproct, or anal pyramid. And as it happens...
In the lower left of this one, you should be able to see a little star-shaped structure; that's the periproct. We have several other partial specimens as well, but these are the two best ones so far.
So, it genuinely does look like a Volchovia or a close relative. So what's the surprise? Well, this beastie is an extremely rare, obscure fossil known from Russia, Norway, a site in the US (apparently; I've not yet tracked down the report) and some undescribed specimens from China. All of those are from the Early and Middle Ordovician, so a new palaeo-continent from a new time period is interesting enough to start with.
The other problem is that nobody knows for sure what they are. Only poor specimens have so far been described, and not many of them; but the only group it looks vaguely similar to are the ophiocistioids, which themselves are a very strange, obscure group somewhere between sea urchins and sea cucumbers. However... the critical features of ophiocistioids (such as the mouth array with its goniodonts) have never been found in the (very small) family Volchoviidae. It's always been assumed that they were there... just too poorly preserved to see them.
The new specimens are good enough that we can rule out a large, ferocious mouth, and there is no sign of the plated tube feet that should also be there. In other words, it's almost certainly a volchoviid, but volchoviids almost certainly aren't ophiocistioids. There's a paper in there, I can assure you.
Caveat: we've only just found the things, so everything might change... this is just our preliminary interpretations.
G'night,
Joe
As usual, though, something else turned up instead. Here it is.
It doesn't look like much, and is only about 3 mm long, but the ring of plates making an undulating margin, combined with the large, irregular plating and no stem or arms, suggests a thing called Volchovia. To check that, we'd really want more specimens, and some of them showing the periproct, or anal pyramid. And as it happens...
In the lower left of this one, you should be able to see a little star-shaped structure; that's the periproct. We have several other partial specimens as well, but these are the two best ones so far.
So, it genuinely does look like a Volchovia or a close relative. So what's the surprise? Well, this beastie is an extremely rare, obscure fossil known from Russia, Norway, a site in the US (apparently; I've not yet tracked down the report) and some undescribed specimens from China. All of those are from the Early and Middle Ordovician, so a new palaeo-continent from a new time period is interesting enough to start with.
The other problem is that nobody knows for sure what they are. Only poor specimens have so far been described, and not many of them; but the only group it looks vaguely similar to are the ophiocistioids, which themselves are a very strange, obscure group somewhere between sea urchins and sea cucumbers. However... the critical features of ophiocistioids (such as the mouth array with its goniodonts) have never been found in the (very small) family Volchoviidae. It's always been assumed that they were there... just too poorly preserved to see them.
The new specimens are good enough that we can rule out a large, ferocious mouth, and there is no sign of the plated tube feet that should also be there. In other words, it's almost certainly a volchoviid, but volchoviids almost certainly aren't ophiocistioids. There's a paper in there, I can assure you.
Caveat: we've only just found the things, so everything might change... this is just our preliminary interpretations.
G'night,
Joe
