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Hi all!

What do you think of this vertebra? It was found long ago, comes probably from marine Kimmeridgian-Tithonian outcrops in the Volga basin, Russia. Doesn't look exactly like plesiosaur, but what else?

7564745.jpg

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Partly eroded plesiosaur centrum, that'd be my opinion

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With that hole in the center of the centrum I wonder if it could be ichthyosaur?

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ichthyosaur centra are very round.  This is almost triangular. I am leaning towards pleisiosaur also. 

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On 6/8/2020 at 3:36 AM, jpc said:

ichthyosaur centra are very round.  This is almost triangular. I am leaning towards pleisiosaur also. 

 

Although it's generally true that ichthyosaur vertebrae are circular in shape when looked at from the axial perspective, their shape does change along their spine. From head to tail their vertebrae start off pentagonal pointing down, then gradually change into their more familiar circular shape to end up almost pentagonal again, pointing up and with the "top cut off". The below image, taken from the Handbook of Paleoherpetology, Part 8, Ichthyopterygia, illustrates these changes.

 

5ee2bdef969fc_Ichthyosaurvertebralshapes.thumb.jpg.1c2a92ede3242bd7af9d0ed6dbffc283.jpg

 

Why I mention this is because some of these shapes, when worn down, may come to look rather triangular when looked at straight-on, as in the photograph of the original poster - especially the cervical vertebrae.

 

However, I do agree that this current vertebra seems to be a worn plesiosaur one. Ichthyosaur vertebrae are easy to recognize by way of their cross-section, which is hour-glass-shaped due to the strongly amphicoelous nature of their body. This is definitely not the case here, with the current specimen rather being platycoelous, a condition more typical of plesiosaur vertebrae. As such, ichthyosaur can be ruled out. Furthermore, the vertebra has the paired fenestra also typical of plesiosaurian vertebrae, which, in live, would have allowed blood vessels to enter and exit the vertebral body.
 

On 6/8/2020 at 2:43 AM, M Harvey said:

With that hole in the center of the centrum I wonder if it could be ichthyosaur?

The hole in the centrum is too small and deep to be an expression of the amphicoelous condition of ichthyosaur vertebrae. However, I've found that a similar dimple can frequently be found on vertebrae identified as pliosaurian. I've since come to assume this as one of the identifying traits of pliosaur vertebrae, as well as a lack of (prominent?) constriction of the vertebral body. Both conditions can be observed in the specimen here discussed.

 

As such, I think we're dealing with a worn - but still awesome - pliosaur vertebrae (gen. et sp. indet.). Very cool find!

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16 hours ago, pachy-pleuro-whatnot-odon said:

 

Although it's generally true that ichthyosaur vertebrae are circular in shape when looked at from the axial perspective, their shape does change along their spine. From head to tail their vertebrae start off pentagonal pointing down, then gradually change into their more familiar circular shape to end up almost pentagonal again, pointing up and with the "top cut off". The below image, taken from the Handbook of Paleoherpetology, Part 8, Ichthyopterygia, illustrates these changes.

5ee2bdef969fc_Ichthyosaurvertebralshapes.thumb.jpg.1c2a92ede3242bd7af9d0ed6dbffc283.jpg

Thanks for this.  Another piece of info learned right here on TFF.

 

 

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16 hours ago, pachy-pleuro-whatnot-odon said:

 

Although it's generally true that ichthyosaur vertebrae are circular in shape when looked at from the axial perspective, their shape does change along their spine. From head to tail their vertebrae start off pentagonal pointing down, then gradually change into their more familiar circular shape to end up almost pentagonal again, pointing up and with the "top cut off". The below image, taken from the Handbook of Paleoherpetology, Part 8, Ichthyopterygia, illustrates these changes.

 

5ee2bdef969fc_Ichthyosaurvertebralshapes.thumb.jpg.1c2a92ede3242bd7af9d0ed6dbffc283.jpg

 

Why I mention this is because some of these shapes, when worn down, may come to look rather triangular when looked at straight-on, as in the photograph of the original poster - especially the cervical vertebrae.

 

However, I do agree that this current vertebra seems to be a worn plesiosaur one. Ichthyosaur vertebrae are easy to recognize by way of their cross-section, which is hour-glass-shaped due to the strongly amphicoelous nature of their body. This is definitely not the case here, with the current specimen rather being platycoelous, a condition more typical of plesiosaur vertebrae. As such, ichthyosaur can be ruled out. Furthermore, the vertebra has the paired fenestra also typical of plesiosaurian vertebrae, which, in live, would have allowed blood vessels to enter and exit the vertebral body.
 

The hole in the centrum is too small and deep to be an expression of the amphicoelous condition of ichthyosaur vertebrae. However, I've found that a similar dimple can frequently be found on vertebrae identified as pliosaurian. I've since come to assume this as one of the identifying traits of pliosaur vertebrae, as well as a lack of (prominent?) constriction of the vertebral body. Both conditions can be observed in the specimen here discussed.

 

As such, I think we're dealing with a worn - but still awesome - pliosaur vertebrae (gen. et sp. indet.). Very cool find!

Well explained.  I have never physically seen an ichthyosaur vertebra so cannot comment further.  However, I am confused about your posting.  Are you suggesting this is a Plesiosaur or a pliosaur vertebra?   

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