Pachystropheus rhaeticus?

[JoeM]

I tried posting something up a few days back but got no reply - I think maybe i made the mistake of posting too much up at once. Well I have now done some minor prep on this chunk of Rhaetic bone bed from Aust Cliff, anyway, and on revealing more of the bone and consulting my new purchase of 'Fossils of the Rhaetian Penarth Group', my confidence in my original conclusion has increased - that this most prominent bone fragment is the end of a Pachystropheus rhaeticus femur or tibia. I guess I was hoping that someone here with a lot more knowledge of these rocks would be able to confim my hunch so I can feel happy labelling it as such!  I want to go back there now...(for reference, bone piece is approx 2.5cm long)

Edited June 21, 2021 by JoeM

[JoeM]

My one other question would be re: the other abraded chunk of bone in the matrix that has lost its cortical layer - I tried to prep it out but it turns out that it is part of a larger bone structure extending deep into the conglomerate - but it isn't easily revealed - perhaps because it has a honeycomb texture of bone interior, the surrounding sediment has managed to cement to it very firmly. I was wondering whether anyone thought it to be worth the effort to try and reveal more of this abraded bone, to get a better feel for the overall shape of it at least?

Here you can see it in-situ (with the removed section put back in original position;

 

and here you can see the bone continuing deeper into the matrix:

[pachy-pleuro-whatnot-odon]

On 6/21/2021 at 7:01 PM, JoeM said:

I tried posting something up a few days back but got no reply - I think maybe i made the mistake of posting too much up at once.

 

Could be, or it could simply be that the right people have somehow missed seeing your post. Also, I haven't bumped into to any people on TFF who collect from Aust Cliff - @Welsh Wizard and @Pterygotus are the only ones I know of so far - though material from this location does show up from time to time. As such, material from this location may be a bit of a niche. I myself have some pieces in my collection, for example, but haven't actually collected at Aust myself, and thus have rather limited knowledge on its fossils. As such, my knowledge comes primarily from what others have told me...

 

On 6/21/2021 at 7:01 PM, JoeM said:

[...] consulting my new purchase of 'Fossils of the Rhaetian Penarth Group'

 

That sounds like a really useful book, so have just ordered it myself. Should have but in a couple of weeks. However, if it contains images of Pachystropheus rhaeticus arm and leg bones, may be you could share them here, either on the thread (be sure to cite your source) or in a PM, and I'll gladly take a look at it to see if your conclusion seems reasonable.

 

On 6/21/2021 at 7:01 PM, JoeM said:

that this most prominent bone fragment is the end of a Pachystropheus rhaeticus femur or tibia. I guess I was hoping that someone here with a lot more knowledge of these rocks would be able to confim my hunch so I can feel happy labelling it as such!  I want to go back there now...(for reference, bone piece is approx 2.5cm long)

 

In any case this it's a really nice find! How did you prep it? That is, I've been told that best results at this location are obtained using acid prep, since the matrix can be rather sticky (not much separation between matrix and bone) and bone soft...

 

Anyway, this is definitely reptile bone, and, without knowing too much of Pachystropheus-anatomy (instead basing myself on nothosaurs), I'd say this does look like a humerus or may be a femur. In itself the shape is reminiscent of a plesiosaur propodial, though those would be much larger (I've got some small/juvenile ones from Aust Cliff, but even those are much larger). Since your primary reptile candidates are, as I believe, P. rhaeticus, plesiosaur and ichthyosaur, the size seems to point towards P. rhaeticus. I'd therefore say your diagnosis is correct, though I wouldn't be able to help you beyond that...

 

On 6/21/2021 at 7:08 PM, JoeM said:

My one other question would be re: the other abraded chunk of bone in the matrix that has lost its cortical layer - I tried to prep it out but it turns out that it is part of a larger bone structure extending deep into the conglomerate - but it isn't easily revealed - perhaps because it has a honeycomb texture of bone interior, the surrounding sediment has managed to cement to it very firmly. I was wondering whether anyone thought it to be worth the effort to try and reveal more of this abraded bone, to get a better feel for the overall shape of it at least?

 

You could try acid prep to see if you can get the bone out with the least damage, though not it's a rather time-consuming process. However, if the cortex really isn't there any more, I don't think it'd be worth investing more effort. Not only will it be a difficult prep due to lack of separation between matrix and bone, but it'll also be very hard to tell where the matrix ends and bone begins... As to the results of your efforts, you'd just end up with a chunk of unidentifiable bone. For, lacking cortex, you'd never know in what direction the one might originally have continued - that is, you'd never be able to confidently establish the original shape of the bone. Still, it could offer you a fun experiment or learning opportunity 

[Welsh Wizard]

Hi.

 

Yes it is a partial pachystropheus femur.

 

You get lots of worn bone pieces in the rhaetic and they are pretty much impossible to identify. Sometimes part of the bone surface may be preserved and you can work out what it is.

 

Nick