Unidentified Triassic reptile bone

[pachy-pleuro-whatnot-odon]

Hi everyone,

I recently acquired the below fossil, taking a chance as to what it might be. It came labelled as Mixosaurus sp. from the Keuper (Upper Triassic) of Kirchberg an der Jagst, but I can't place the bone...

 

 

Initially, I thought it could be a broken mixosaur coracoid, though the shape doesn't match at all. In the below image the break is circled in blue, with the red circle marking a projection from the bone that I would not expect to be present if the bone were indeed a (mixosaur) coracoid, as shown in the drawing next to it (from Jiang, Schmitz, Hao and Sun, 2006. A new mixosaurid ichthyosaur from the Middle Triassic of China). Moreover, according to the Handbook of Paleoherpetology on ichthyopterygians, mixosaurs were no longer around in the Upper Triassic. Nor is it the coracoid of a more derived species of ichthyosaur, as these have neither notch nor the aforementioned projection - as is illustrated by the image below (don't mind the incorrect bone ID on the label).

 

 

Thus, in line with a suspicion I already had, it doesn't look like this is a mixosaur coracoid at all. But what could it be then? Well, one option seems to be that this could be a pelvic bone, either of a shastasaurid or other early ichthysaur like Cymbospondylus sp. or Besanosaurus sp., to judge by the notch at the top of the bone. The below drawings, taken again from the Handbook of Paleoherpetology, demonstrate what I mean, as does the supplied image of a shastasaurid pelvic girdle from China (figure 4 from Shang & Chun, 2009. On the occurrence of the ichthyosaur Shastasaurus in the Guanling biota (Late Triassic), Guizhou, China):

 

 

Unfortunately, however, most of the species in which this condition occurs don't seem to have survived beyond the Middle Triassic. What's more, reference material I have of a cast of Besanosaurus sp. taken in the Museo Civico dei Fossili die Besano don't make things much clearer for that particular species, as such a notch cannot be observed (nor am I entirely sure it's visible in the above photograph of the Shastasaurus tangae):

 

 

Similarly, the best preserved Cymbospondylus sp. specimen at the Zoological and Palaeontological Collections of the University of Zürich is of little contribution, because of it lacking the hind part of its body. A second specimen, however, does seem to preserve the pubis (albeit in less direct association):

 

 

This being the case, could it my bone be an early ichthyosaurian pubis? Or should we still rule that out for the above reasons (i.e., the species showing the characteristics notch not being recorded for the Upper Triassic)? What about other options? As can be seen in the below image, the shape of the bone looks kind of reminiscent of a plesiosaur (here , at the Zoological and Palaeontological Collections of the University of Zürich) pubis, though obviously a lot smaller.

 

 

Could it be, then, that rather than stemming from an ichthyopterygian the bone derives from a sauropterygian? If so, placodont is not very likely, since, as far as I know, 1) these were not around during the Upper Triassic, and 2) the shape of the bone does not seem to match elements from either pectoral or pelvic girdles amongst the little reference material I have of Placodus gigas. Something of a pachypleurosaur then? Doesn't look likely either, based on some reference material I took of a Serpianosaurus mirigiolensis specimen at the Museo dei fossili del Monte San Giorgio in Meride:

 

 

Looking at nothosaurid specimens from the Paläontologische Sammlung of the MUT in Tübingen (first) and Zoological and Palaeontological Collections of the University of Zürich (rest: Ceresiosaurus sp.), although not providing a direct match, seem more promising as comparison material:

 

[pachy-pleuro-whatnot-odon]

(continuation)

 

 

 

This provides me with three different hypotheses on the origin of the bone:

1. The pubis of an early ichthyosaurian that either survived into the Upper Triassic - unless the bone itself was wrongly attributed to the Upper Triassic and actually derives from the Middle Triassic.
2. An element of the pectoral or pelvic girdle of a nothosaurid - e.g. coracoid or pubis.
3. The pubis of an early plesiosaurian.

 

What do you guys think? Am I on the right track? Any input would be greatly appreciated.

[Tidgy's Dad]

But very interesting.

[pachy-pleuro-whatnot-odon]

@RuMert, you wouldn't happen to have any experience with Triassic marine reptiles, would you?

[RuMert]

Nope, still much to explore in the Jurassic

[pachy-pleuro-whatnot-odon]

47 minutes ago, RuMert said:

Nope, still much to explore in the Jurassic

Pity, but too true Thanks for responding anyway

[pachy-pleuro-whatnot-odon]

@Tooth or Dare, @jdp, as you guys are one of the few I've met on here dealing with Triassic material: I know this is a marine specimen, and as far as I know you're dealing with continental material, but would you have any ideas on what I might be dealing with here? At least the Upper Triassic age fits...

 

Also, @Crazyhen, as I've seen multiple posts from your end dealing with Triassic marine reptiles: would you recognize the bone in question from somewhere?

[Crazyhen]

On 12/6/2020 at 8:54 AM, pachy-pleuro-whatnot-odon said:

@Tooth or Dare, @jdp, as you guys are one of the few I've met on here dealing with Triassic material: I know this is a marine specimen, and as far as I know you're dealing with continental material, but would you have any ideas on what I might be dealing with here? At least the Upper Triassic age fits...

 

Also, @Crazyhen, as I've seen multiple posts from your end dealing with Triassic marine reptiles: would you recognize the bone in question from somewhere?

Do you have the size of the bone?  This is a very interesting piece.

[pachy-pleuro-whatnot-odon]

12 minutes ago, Crazyhen said:

Do you have the size of the bone?  This is a very interesting piece.

Hi, thanks for asking! And, sure, I've marked them in the image below. If you need any further dimensions, just let me know...

 

[Crazyhen]

Does it look like part of a placodont's vertebrae?

 

https://www.cambridge.org/core/journals/netherlands-journal-of-geosciences/article/possible-pararcus-diepenbroeki-vertebra-from-the-vossenveld-formation-triassic-anisian-winterswijk-the-netherlands/BB75CE8D0396EC5ABF12DC4C93DE7D21

[jdp]

Coracoid or pubis seems right but couldn't really tell you about the taxonomy as I'm not a marine reptile expert, sorry.

[pachy-pleuro-whatnot-odon]

17 minutes ago, jdp said:

Coracoid or pubis seems right but couldn't really tell you about the taxonomy as I'm not a marine reptile expert, sorry.

No matter. Thanks for weighing in, though!

[pachy-pleuro-whatnot-odon]

16 hours ago, Crazyhen said:

Does it look like part of a placodont's vertebrae?

 

Thank you! I see what you mean! Interesting suggestion! Hadn't thought about that, seeing as the Placodus gigas reference material I have from Naturkundemuseum in Stuttgart and Naturmuseum Senckenberg in Frankfurt don't seem to exhibit such a feature (some bonus material thrown in for good measure:

 

Naturkundemuseum, Stuttgart

 

 

 

 

 

 

 

 

 

Naturmuseum Senckenberg, Frankfurt

 

 

 

 

 

 

 

 

 

Zoological and Palaeontological Collections of the University of Zürich

 

 

 

 

 

 

 

Now I know the article and vertebra in question refer to Pararcus diepenbroeki. But as I understand it, this species has only been found in Winterswijk, in the Netherlands, and hasn't been found elsewhere. In addition, it's currently temporarily restricted to the Middle Triassic. Assuming that the given date for my bone is correct, this makes it a less likely match, I think. More importantly, however, my bone is entirely flat, without any sculpting that could indicate the three-dimensional character of the vertebral processes you're suggesting. Notwithstanding, the closer analysis of my placodont reference material has led to a discovery I had not previously considered. Below are some images of the Senckenberg museum placodus's pelvic girdle. As can be seen, this pubis too has a notch.

 

 

As such, I'm growing more and more convinced that the bone I have is a pubis. The question, though, remains: from what animal ? The more likely option, at this point in time, would have it be a sauropterygian - either a placodont, nothosaurid, or early plesiosaurian - since the notched condition seems more prevalent in this taxon, versus ichthyopterygia, where the condition is more restricted, both temporarily as well as in terms of species it occurs in.

[pachy-pleuro-whatnot-odon]

@va paleo, I just read your introduction, and since you mention you work mostly with Triassic material, I was wondering whether you might be familiar with marine reptiles from this era?

Similarly, @Pterygotus, would you have any experience with the above type of bone material?

[Welsh Wizard]

Hi

 

Interesting bone. I don’t think it’s a partial coracoid. Not sure I can add much but the neurals of pachystropheus from Aust look similar.

 

Ive borrowed this pic of Martin Hicks’s website, I’m sure he won’t mind.

 

 

N

[pachy-pleuro-whatnot-odon]

Hi @Welsh Wizard,

Thanks for having a look and for the suggestion! I can certainly see where you got the idea. However, again, I don't think a neural arch is the solution for my bone though. If you look at the pictures below, for instance, one of the first things you'll probably notice is that what, in the Pachystropheus, is the neural arch's articulation with the vertebra anterior to it on the spine (circled in red) is located on the opposite side of the notch on my bone - that is, not on the side of the spinous process, but rather closer to where the vertebral body would supposedly have attached. I haven't seen such a configuration before, and am not sure whether it would actually exist. Secondly, while the break from the vertebral body on the Pachystropheus vertebra (marked with a  blue line) is rather straight - as it follows the curve of the vertebra it would've once been attached to - this is not the case for the break in my bone, which runs in a curve that seems unlikely to have attached to a vertebral centrum. A third point is that the bottom part of the Pachystropheus neural arch is slightly curved forward, out of the matrix, so as to make space for the neural canal. Again, such a feature is not present in my bone. Moreover, this configuration would mean my neural arch would have a flaring spinous process, which I've also not seen before.

 

 

Your opinion on the bone not being a coracoid is well taken though, and (/as it?) conforms to my own idea of the bone being some kind of sauropterygian pubis.

 

Thanks again for thinking along!

[Welsh Wizard]

42 minutes ago, pachy-pleuro-whatnot-odon said:

Hi @Welsh Wizard,

Thanks for having a look and for the suggestion! I can certainly see where you got the idea. However, again, I don't think a neural arch is the solution for my bone though. If you look at the pictures below, for instance, one of the first things you'll probably notice is that what, in the Pachystropheus, is the neural arch's articulation with the vertebra anterior to it on the spine (circled in red) is located on the opposite side of the notch on my bone - that is, not on the side of the spinous process, but rather closer to where the vertebral body would supposedly have attached. I haven't seen such a configuration before, and am not sure whether it would actually exist. Secondly, while the break from the vertebral body on the Pachystropheus vertebra (marked with a  blue line) is rather straight - as it follows the curve of the vertebra it would've once been attached to - this is not the case for the break in my bone, which runs in a curve that seems unlikely to have attached to a vertebral centrum. A third point is that the bottom part of the Pachystropheus neural arch is slightly curved forward, out of the matrix, so as to make space for the neural canal. Again, such a feature is not present in my bone. Moreover, this configuration would mean my neural arch would have a flaring spinous process, which I've also not seen before.

 

 

Your opinion on the bone not being a coracoid is well taken though, and (/as it?) conforms to my own idea of the bone being some kind of sauropterygian pubis.

 

Thanks again for thinking along!

thanks. It does look like an ilium, Ischium or pubis. Some strange things in the Triassic.

[pachy-pleuro-whatnot-odon]

Hi @Mahnmut,

 

I just bumped into your excellent thread on the Triassic anatomical models you made last year:

 

Might you, from this experience, have any insights as to what the above bone might be?

[Mahnmut]

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

Hi @Mahnmut,

 

Might you, from this experience, have any insights as to what the above bone might be?

Hi and thanks!

I have been asking myself the same thing.

Finding sources on Placodontia was not so easy, what I finally used for Placodus was this:

https://www.researchgate.net/figure/Placodus-gigas-Agassiz-1839-from-the-German-Upper-Muschelkalk-Middle-Triassic-of-the_fig9_272322611

 

For Cyamodus and Henodus I have close to no idea what they look like beneath the shell.

Looking at placodontia, I would have said a pubis is the closest call, but after looking at some images from sauripterygia and ichthyosauria an ischium or coracoid is as plausible.

Can you take a closer look at the rim of your specimen and try do find out where there is a free/smooth border, where there are hints of contact to other bones and where there may be parts broken of? Maybe that can narrow it down.

Sorry to be of no more help.

I will keep an eye on this though.

Best regards,

J

[pachy-pleuro-whatnot-odon]

4 hours ago, Mahnmut said:

Hi and thanks!

I have been asking myself the same thing.

Finding sources on Placodontia was not so easy, what I finally used for Placodus was this:

https://www.researchgate.net/figure/Placodus-gigas-Agassiz-1839-from-the-German-Upper-Muschelkalk-Middle-Triassic-of-the_fig9_272322611

 

For Cyamodus and Henodus I have close to no idea what they look like beneath the shell.

Looking at placodontia, I would have said a pubis is the closest call, but after looking at some images from sauripterygia and ichthyosauria an ischium or coracoid is as plausible.

Can you take a closer look at the rim of your specimen and try do find out where there is a free/smooth border, where there are hints of contact to other bones and where there may be parts broken of? Maybe that can narrow it down.

Sorry to be of no more help.

I will keep an eye on this though.

Best regards,

J

You too, thanks for willing to help out!

 

Actually, I had myself also found the reference to figure 14 of Diedrich, 2013. Review of the Middle Triassic "sea cow" Placodus gigas (Reptilia) in Pangea's shallow marine macroalgae meadows of Europe (reproduced below for sake of convenience), which is what made me reconsider the broader spectrum of sauropterygians for the origin of my bone, rather than just the plesiosaurian clade. I thought I had included it in the thread too, but must've forgotten somewhere...

 

 

Anyway, I'll have a look and draw up an overview of likely articulation surfaces and breaks, though it may be a couple of days due to my schedule at the moment.

 

As to Cyamodus and Henodus, although I've seen some fossils in museums I've visited, I was unfortunately never interested enough to take proper reference material (not that the way these specimens were exhibited would've made that overly easy). But the Triassic generally being a relatively obscure and little studied age, and these species being so regionally restricted, I can totally imagine how difficult it must've been to find sufficient information. So, by way of giving back to the community, let me share what material I have...

 

Henodus chelyops specimen at the Paläontologische Sammlung, MUT Tübingen

 

 

 

 

 

 

 

 

 

Henodus chelyops cast at the Naturmuseum Senckenberg in Frankfurt

 

 

 

 

 

 

 

 

 

Placodus gigas and Placochelys placodonta dental configurations at the Naturmuseum Senckenberg in Frankfurt

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Overview of placodont dental configurations at the Zoological and Palaeontological Collections of the University of Zürich

 

[pachy-pleuro-whatnot-odon]

On 12/13/2020 at 3:14 PM, Mahnmut said:

Can you take a closer look at the rim of your specimen and try do find out where there is a free/smooth border, where there are hints of contact to other bones and where there may be parts broken of? Maybe that can narrow it down.

Okay, so I had a look today, but feel I need to add a disclaimer, as my answer will be very much speculation. Unfortunately, the bone hasn't been freed from matrix too much along the sides, so there's no real telling how thick some of the sides are and whether they might represent articulation surfaces or otherwise. The below is therefore an interpretive image, based either on clearly visible signs, but for the most part on my experience with other bones to deduce how orientation of bone fibres, roughness of bone texture, thickness of bone, etc. work together. I've used red colouring to indicate clear breaks, dark-blue to indicate certain articulation surfaces, light-blue lines to indicate possible ones, dark-green to mark areas where the bone is complete and doesn't articulate, and light green where I'm fairly certain the bone doesn't articulate.

 

 

As you can see, the bone appears coherent apart from the bottom section missing, and has one, possibly two articulation surfaces. The dark-blue area looks thickened and rather rugose, and I'm thus pretty sure it's an articulation surface. The light-blue area also seems some what thicker, which suggests to me that, notwithstanding the radial orientation of bone fibres there, this area may also have articulated with something. This radial patterning is much more noticeable in the light-green area, though, which is also much thinner. I, therefore, do not regard this as an articulation surface.

 

But, the best evidence is to see for yourself. So I've tried to take a number of photographs from different angles in hopes you can reproduce (or, at least, re-evaluate) my findings.

 

 

 

[pachy-pleuro-whatnot-odon]

In the meantime, I've found below images of nothosaurid pectoral and pelvic girdles (as illustrated in chapter 4 of Williston's 1925 The Osteology of Reptiles). Which not only makes it easier to interpret and compare the bone versus the bones of nothosaurids, but also convinces me that my bone doesn't come from a nothosaur.

 

 

Similarly, I don't think it's an ichthyosaur coracoid or pubis, as 1) the shape of those bones is more rounded; 2) their notches are smaller, and almost enclosed; and 3) only early genera have these notches to start with, genera that - if dating for my bone is correct - were no longer around at the time this bone was deposited.

 

After having reviewed the images above on Placodus gigas' pubis, I'm now also coming back on this being a placodont pubis, for much the same reasons as I don't think this is an ichthyosaur pubis: 1) the pubis of Placodus gigas is a lot more rounded, 2) with the notch almost enclosed in the bone.

 

That is, the right side of this bone has a distinct wavy pattern that doesn't seem to have been caused by breakage, and mus therefore be significant (it appears almost bifurcated). I find this general shape, as well as the big, open notch, to correspond most to the pubis bone seen in plesiosaurs, traits that remain visible even in the most derived types (in the images below, areas of same colour indicate what I consider to be corresponding parts of the bone):

 

 

Rhomaleosaurus victor cast at the Zoological and Palaeontological Collections of the University of Zürich

 

 

 

 

 

 

 

 

 

 

 

Brancasaurus brancai pelvic girdle. Figure 22 from Sachs, Hornung and Kear, 2016. Reappraisal of Europe’s most complete Early Cretaceous plesiosaurian: Brancasaurus brancai Wegner, 1914 from the "Wealden facies" of Germany

 

 

 

 

 

 

 

 

 

 

 

 

 

Elasmosaurus ischiadicus, plate I & Pubes of Elasmosaurus snowii, figure 3, both from Williston, 1906. North American Plesiosaurs: Elasmosaurus, Cimoliasaurus, and Polycotylus

[Pemphix]

The piece is coming from the Anthrakonitbank in Kirchberg which is Middle Triassic, Ladin, Longobard, lower Keuper (Lettenkeuper), Erfurt-Formation, ku2.

The only known placodont from the Anthrakonitbank is Psephosaurus suevicus, which is very rare and known only by some armor-plates and teeth. I don't think, that your piece belonging to this placodont.

Concerning Ichthyosaurs: the only known and valid species in Germany from the middle triassic are (according to MAISCH&MATZKE 2000: The Ichthyosauria): Contectopalatus, Phalarodon, Phantomosaurus and Cymbospondylus. None of them are known in the Lower Keuper - they are pretty rare in the Lower and upper Muschelkalk below, too. 

Since the Anthrakonitbank is a immature Bonebed with a strong (shallow) marine fauna, high-marine fauna is not to be expected.

No plesiosaurs known from this horizon, the first (and only one till now) is from much more younger rhaetian of age (upper keuper, boundary to lowermost jurassic; Westphaliasaurus simonsei).

Pretty often are Sauropterygian remains, namely those from Nothosaurs, most often specis is N. edingerae. So my best guess would be a sauropterygian remain (most likely nothosaurid).

 

 

[Mahnmut]

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

 

 

Rhomaleosaurus victor cast at the Zoological and Palaeontological Collections of the University of Zürich

 

 

 

 

 

 

 

 

 

 

In other depictions of plesiosaur pelves Ischium, pubis and even coracoids seemed strangely similar, but looking at the Rhomaleosaurus, the ischium seems to be a  better fit than the pubis in my eyes.  So Ischium , maybe pubis, of a smallish animal not to far from plesiosauria?

[pachy-pleuro-whatnot-odon]

On 12/7/2020 at 8:59 AM, Crazyhen said:

Does it look like part of a placodont's vertebrae?

 

https://www.cambridge.org/core/journals/netherlands-journal-of-geosciences/article/possible-pararcus-diepenbroeki-vertebra-from-the-vossenveld-formation-triassic-anisian-winterswijk-the-netherlands/BB75CE8D0396EC5ABF12DC4C93DE7D21

For those interested in more information on this rare placodont, Pararcus diepenbroeki, I just bumped into another paper on it, which not only provides its systematic description, but includes quite a bit of material of the holotype specimen as well: https://doi.org/10.4202/app.2012.0147