Plesiosaurus Vert...Maybe

[Planko]

Hi All. I found this recently at NSR. I do believe it is a Plesiosaurus vertebrae. Looking around to make sure before I label and I have confused myself. Looked at  too many websites. So, is it a Plesiosaurus Vert? 

 

Thanks in advance for your help?

 

[Tidgy's Dad]

I couldn't say if it's the genus Plesiosaurus, but it does look like a plesiosaur to me. 

[RuMert]

Definitely plesiosaur, probably caudal (looks like it has chevrons on the bottom side)

[Planko]

Thanks for the help...

[jpc]

definitely a plesiosaur caudal.  I also see chevron attachment points (rather than actual chevrons). Plesiosaurus is but one genus of these things.  I have no idea which plesiosuars are known from the NSR, but I doubt it can be IDed to the genus.  

[pachy-pleuro-whatnot-odon]

Yup, plesiosaur, though you'd be hard-pressed to identify it by genus and species. You can tell it's plesiosaur by the platycoelous condition of the vertebral centrum, the slight compression in the middle of the centrum when looking at it from the axial perspective, as well as from the two foramina that would've allowed blood-vessels to enter the vertebral centrum. I'm not too sure whether this is a caudal vertebra, as suggested by @RuMert and @jpc, however, as 1) I always thought the paired foramina were a trait absent in caudal vertebrae; and 2) chevrons seem to be connected between vertebrae and therefore have facets both anterior and posterior to the vertebral axis. Both points seem to be corroborated by the images below (albeit that the first illustration figures specimens from an early pliosauroid that wouldn't have been around at the time the Ozan Formation would've been laid down):

 

Figure 5 from Zverkov and Arkhangelsky, 2015. Youngest Occurrences of Rhomaleosaurid Plesiosaurs Indicate Survival of an Archaic Marine Reptile Clade at High Palaeolatitudes

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figures 5 & 6, respectively, taken from Otero, Soto-Acuña, Vargas and Rubilar-Rogers, 2014. A new postcranial skeleton of an elasmosaurid plesiosaur from the Upper Cretaceous of central Chile and reassessment ofCimoliasaurus andium Deecke

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I, moreover, went back through my collection of photographs taken in museums to have a look a plesiosaur skeletons - and especially their tail-chevrons there - and found the same: the chevrons seem to be consistently attached on articulation-surfaces between vertebra.

 

Posterior section, including tail and chevrons, of Peloneustes philarcus from the Paläontologische Sammlung, MUT Tübingen.

 

 

 

 

 

 

 

 

 

 

 

Liopleurodon ferox and indet. plesiosaur tail sections from Paleospace in Villers-sur-Mer. Although reproductions and lacking their chevrons, informative for their lack of facets to which the chevrons could be attached.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Peloneustes philarcus and Cryptoclidus eurymerus tail sections at the Senckenberg Museum. Note in the one case chevrons are consistently placed in between the vertebra, and in the other that, although the chevrons themselves are missing, the articulation surfaces are positioned between the vertebrae.

 

 

 

 

Tail section of Plesiosaurus dolichodeirus at the Naturalis Biodiversity Center. Note the clear articulation surfaces for chevron attachment between the vertebrae.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Considering the visible facets on the NSR-vertebra rib attachment sites, I think we're dealing with a cervical. Moreover, one of the more anterior ones, close to the head, since that's where rib attachment starts ventrally to the vertebral centrum, gradually moving up towards the neural arch when reaching the back of the animal. The below image illustrates this nicely:

 

Figure 6 from Noë, Taylor and Gómez-Pérez, 2017. An integrated approach to understanding the role of the long neck in plesiosaurs.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I think the vertebra discussed probably comes from somewhere between B and C.

 

As to genus and species: as said, this will be tricky. And though plesiosaur remains from the Ozan/NSR seem rather infrequent and oft remain unidentified, the Cretaceous date for these finds is rather telling in itself - not too many plesiosaurs were still around by that time. I'd say your specimen is not a pliosaur, though, seeing as only one species has ever been discovered in the US - Brachauchenius lucasi - the lack of notochordal pit and their vertebrae typically being more rounded and robust. Thus either an elasmosaur or polycotylid. I'd go for Leptocleidia, however, a group derived from the Jurassic Cryptoclididae, which I've found to have their vertebral foramina not on the ventral, but rather the dorsal side. That means that the plesiosaur whose vertebra this is could either fall within Leptocleididae or, depending on which phologeny you follow for Polycotylidae, in Polycotylidae. See below image for further reference (which is what I like to use as a personal reference):

 

Figure 5 from Benson, Ketchum, Naish and Turner, 2012. A new leptocleidid (Sauropterygia, Plesiosauria) from the Vectis Formation (Early Barremian–early Aptian; Early Cretaceous) of the Isle of Wight and the evolution of Leptocleididae, a controversial clade.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Plesiosaurus, by the way, as has already been pointed out, is only one genus within the broad clade of sauropterygia called plesiosaurs, and a rather early one at that. Plesiosaurs, in a general sense, encompasses the various sub-clades, known as pliosaurs, elasmosaurs, and polycotylids. Here elasmosaurs can broadly be defined as that group of derived plesiosaurs that have an extremely elongated neck and small head (much like early plesiosaurs - and the genus Plesiosaurus - though with the mentioned characteristics taken to the extreme), while pliosaurs are typically described as more robust, short-necked apex-predators with giant heads. Polycotylids fall somewhere in between the early plesiosaur and pliosaur body plans, and have shorter necks and long narrow snouts. However, don't be fooled into believing that plesiosaurs are defined by morphotypes, as there are pliosauroid plesiosaurs out there (i.e. plesiosaurs that look like pliosaurs) as there are plesiosauroid pliosaurs. Another example is that it's far from clear where polycotylids fall in the plesiosaur family tree. They share certain characters with pliosaurs, but do so with plesiosaurs as welll. In fact, all of this gets so confusing, that you'll often see people just refering to plesiosaurs in the broadest definition possible, which is "plesiosaur". Whence, I suspect, your own confusion.

 

Hope this is of some help.

[RuMert]

Looks like a paper

[Planko]

WOW! Thank you for the information. I will have to read it many times to get it all. Your time is greatly appreciated. 

[jpc]

pachy-p makes a good point.

 

here is photo of the base of two plesio verts, one dorsal and one caudal.  The dorsal (bigger of the two) has two obvious foramina. They are more random in the caudal, but yes, the chevron attachments are on the very edge.  So I think the original bone in question is indeed NOT a caudal, based on the chevron attachment points.  The third photo (in original post) shows two very obvious facets at the base of the vert.  The placement of these should be a good clue as to where exactly on the body this bone comes from.  I am not sure the answer without looking up a few plesiosaur papers.   

  

[RuMert]

Well, if not caudal, then cervical, simple as that:)

[pachy-pleuro-whatnot-odon]

On 7/6/2020 at 4:49 PM, RuMert said:

Looks like a paper

 

Thanks! Certainly took me long enough to research and write this up For at the start all I had was a feeling that this was not a caudal but a cervical. Yet, as I have no caudal vertebrae with chevron attachments in my personal collection, I had to resort to checking reference images and photographs I took in the various museums I've visited. All in all, though, it was fun and educational (for myself, as hopefully for others) to do

[pachy-pleuro-whatnot-odon]

On 7/6/2020 at 5:42 PM, jpc said:

The third photo (in original post) shows two very obvious facets at the base of the vert.  The placement of these should be a good clue as to where exactly on the body this bone comes from.  I am not sure the answer without looking up a few plesiosaur papers.

 

My identification as a cervical is based on the image above (from Noë, Taylor and Gómez-Pérez, 2017. An integrated approach to understanding the role of the long neck in plesiosaurs):

 

For if you study those images, you'll notice that, in the progression of vertebrae from C through F - i.e. from cervical through dorsal, according to their placement on the skeleton - the rib facets-move from an almost ventral position to a lateral placement on the neural spine. Now, obviously, the exact placement and shifts of the facets will differ per species, but the picture does illustrate the general tendency. This makes sense, since the neck, near the head, would be rather narrow and shallow, but obtains more musculature, and therefore girth, towards the torso. Part of how this girth is obtained is by moving the costae/ribs into a more lateral position. Therefore, the more ventrally located the facets, the closer to the head the vertebra would have been positioned - though, again, more exact placement would require more precise knowledge of the species involved.

 

A "life" illustration of this point can nicely be seen in the below photograph, taken in the Senckenberg Museum in Frankfurt, of a Cryptoclidid (incorrectly reported above as Cryptoclidus eurymerus, since the museum itself has classified it as Cryptoclidus oxoniensis, though FossilWorks calls it Plesiosaurus oxoniensis). Though plenty of ribs are missing and the photograph might have been taken a bit far away to make out all of the details, where ribs are available, you can see them move from a more ventral position to attachment on the neural spine. And where the ribs themselves are no longer present, the facets still are, showing a similar transgression.

 

Nice set of verts, though, @jpc! I especially like the caudal, with the chevron facets. Wish I had me one of those!

[jpc]

I can't see any verts where the ribs attch at a straight down (ventral) position, but maybe the species found in TX does this.  On the other hand, I imagine that this condition is most likely in the neck, fairly close to the skull.  So I agree, cervical vert of a plesiosaur of some kind.  Good find.

 

[facehugger]

Great find!