Middle Triassic ichthyosaur vertebra

[pachy-pleuro-whatnot-odon]

Early June, two years ago, I found this ichthyopterygian vertebra in a small nodule out of the northern French Middle Triassic, from the Upper Muschelkalk. Almost two years to the day later a friend of mine helped me complete its preparation this month. When done, one of the first things that struck me were the elongate, and slightly tilted rib attachment sites. As far as I know, such rib attachment sites do not occur in any parvipelvian ichthyosaur species, which, instead, have round, button-like, attachment sites, especially on dorsal vertebrae as my find is.

 

Now I realise that ichthyosaur vertebrae typically hold very little diagnostic value, but I was wondering whether the peculiar rib attachments might be indicative of a super-family, family or even genus, so that I can label the vertebra more informatively than "indet. basal ichthyopterygia". Nothing is known of the species at the sites where I found this, though, based on size alone, Cymbospondylus sp. seems like a good candidate. Any other ideas?

 

@Pemphix @sander @paulgdls @Welsh Wizard @Crazyhen

 

Dimensions of the specimen: 41mm (diameter) x 21 (depth)

 

[pachy-pleuro-whatnot-odon]

Hi all,

 

As there hasn't been any followup to my post either here or on the Dutch forum, I was thinking of taking my question to a more dedicated ichthyosaur researcher. Currently up for consideration are Dean Lomax (Jurassic ichthyosaurs, I believe), Valentin Fischer (mostly terminal-period ichthyosaurs from the Late Jurassic and Early Cretaceous, from what I've read) and Darren Naish (who I know as a more general science writer, though with excellent blogposts on ichthyosaurs of all times). Would anybody here be able to recommend me whom best to contact (first)? Or may be have an alternative suggestion? Thanks again!

[JohnJ]

I am not as familiar with ichthyosaurs.  Is it possible this is an anomaly of plastic deformation or a positional characteristic?

[Welsh Wizard]

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

Hi all,

 

As there hasn't been any followup to my post either here or on the Dutch forum, I was thinking of taking my question to a more dedicated ichthyosaur researcher. Currently up for consideration are Dean Lomax (Jurassic ichthyosaurs, I believe), Valentin Fischer (mostly terminal-period ichthyosaurs from the Late Jurassic and Early Cretaceous, from what I've read) and Darren Naish (who I know as a more general science writer, though with excellent blogposts on ichthyosaurs of all times). Would anybody here be able to recommend me whom best to contact (first)? Or may be have an alternative suggestion? Thanks again!

I know Dean.

 

He’s always really helpful and very knowledgable, just drop him a message on Facebook if you’re on it.

 

Nick

[pachy-pleuro-whatnot-odon]

8 hours ago, JohnJ said:

I am not as familiar with ichthyosaurs.  Is it possible this is an anomaly of plastic deformation or a positional characteristic?

 

Although I hadn't considered it yet, I don't think this is an issue of plastic deformation, as the rest of the vertebra is in such perfect shape. I had thought of the positional aspect and, indeed, did find that articulation surfaces can appear a bit more elongate in caudal vertebrae in more derived species of ichthyosaur. However, in these cases the point of attachment has also shifted, from the sides onto the base of the vertebral centrum - from which I suspect that the examples I've seen no longer show the attachment sites of ribs, but rather of chevrons.

 

Other things I've considered are a possible pathology - though it would strike me as odd to see one so consistently present on both sides of the vertebra - and the possibility of the vertebra belonging not to a Middle Triassic ichthyosaur, but instead to Blezingeria ichthyospondyla. The top left vertebra in below image, for example, also seems to have elongate sites for rib attachment. However, 1) this is the only example of a B. ichthyospondyla vertebra I could find exhibiting this character; and 2) Blezingeria vertebrae are thickly bevelled, with only the very middle of the centrum being concave, whereas my vertebra is concave all the way to the edge...

 

(Source: Wikimedia Commons)

 

 

7 hours ago, Welsh Wizard said:

I know Dean.

 

He’s always really helpful and very knowledgable, just drop him a message on Facebook if you’re on it.

 

Nick

 

Thanks, Nick! I suspected as much, so I'll give him a try then

[sander]

Hi Pachy,

I saw your message on Paleontica, but i did not react there at the time.

The reason for that is that I am struggling with the identification of vertebrae like these myself too.

The thing is that for the Jurassic and Cretaceous vertebrae like these are indeed ichthyosaur, but in the Triassic there are more kinds of animals with this hourglass shaped intersection.

For instance Placodus, Omphalosaurus (which is an ichthyosaur, but a weird one) and indeed Blezingeria. I had contact with Feiko Miedema on a few of my fossils, but I think Dean Lomax is indeed more of a specialist on Ichthyosaurs.

[pachy-pleuro-whatnot-odon]

5 hours ago, sander said:

Hi Pachy,

I saw your message on Paleontica, but i did not react there at the time.

The reason for that is that I am struggling with the identification of vertebrae like these myself too.

The thing is that for the Jurassic and Cretaceous vertebrae like these are indeed ichthyosaur, but in the Triassic there are more kinds of animals with this hourglass shaped intersection.

For instance Placodus, Omphalosaurus (which is an ichthyosaur, but a weird one) and indeed Blezingeria. I had contact with Feiko Miedema on a few of my fossils, but I think Dean Lomax is indeed more of a specialist on Ichthyosaurs.

 

Thanks for your suggestions! It is indeed true that during this time period there were more marine reptiles with hourglass-shaped vertebra than just ichthyosaurs. As noted above, I did already consider Blezingeria previously, but don't find the vertebrae too good a match. I hadn't considered Placodus, however, as this intuitively didn't feel like the source of my vertebra (which, having handled quite a few ichthyosaur vertebrae, actually does feel ichthyosaurian to me). But it'd be good to exclude it as an option in an educated fashion. I thus went through my reference material on Placodus, and, if the border around the vertebral centrum isn't a lot thicker than in ichthyosaurs as with Blezingeria, then I think the below photographs will illustrate that Placodus-vertebrae are much thicker/axially longer than are ichthyosaurian vertebrae, even at this stage in their development.

 

Placodus gigas at the Museum am Löwentor, Stuttgart

 

 

 

 

Placodus gigas and close-ups for cervical, pectoral, dorsal, lumbar and caudal vertebrae at the Naturmuseum Senckenberg in Frankfurt

 

 

 

Source: online vendor

 

 

For comparison, here are a couple of Middle Triassic ichthyosaur vertebrae (left: ?Pessanosaurus [source]; right: ?Cymbospondylus [source]):

 

 

In that respect it's a true shame that the palaeobiota of the location where I found the vertebra has not been described - though I had heard of (and, in part, seen) Placodus gigas, Cyamodus sp. and ?Paranothosaurus having been found there, along with what friends of mine are quite certain are ichthyosaur vertebrae. I've even been shown an odd small mandible from this location which was presented as being ichthyosaurian (regrettably no photograph) with the purpose of me evaluating whether it is or not. Unfortunately, I didn't know quite what to make of it, since the small teeth were rather robust and pill-shaped. Which makes your suggestion of Omphalosaurus the more interesting, as - even though, looking at the jaw directly laterally, with most of it still embedded in matrix, I could only see interspersed teeth of what may have been the first tooth row - the teeth were, in my opinion, reminiscent in shape of the ones in the below image of Omphalosaurus (source):

 

 

 

Anyway, I'll see if I can get in touch with Dean somewhere next week, and will report back if and when I have something

[pachy-pleuro-whatnot-odon]

Just got word back from Dean, who was indeed kind enough to share his thoughts on this. He believes it to be a transitional - or as he described it "merge" - dorsal-to-caudal vertebra. Though I have never seen one of those before, in a way it makes sense, as attachment faces on caudal vertebrae are elongated with respect to their ventrally attached chevrons and, apparently, rib facets already become elongated as the ribs move down the side of the vertebrae towards the back of the back. I hadn't considered this myself, as, on the one hand, like I said, I've never seen such a vertebra either in person or illustrated, and,  on the other, the vertebra looked like a perfectly normal dorsal vertebra to me. But you live and learn 

 

In any case, it would appear that the rib facets on this vertebra are non-diagnostic. Also, there was no hesitation from Dean about this ichthyosaurian, so I'm taking that as confirmation for its identification as basal ichthyopterygia.

Edited July 7, 2021 by pachy-pleuro-whatnot-odon

[sander]

Wouldn't it be called a sacral vertebra then? I mean that is the area between dorsal and caudal vertebrae in other animals?
And it is good to know that Dean is so friendly, I might show him a few of my possible ichthyosaur vertebrae too then sometime soon. Maybe he can help me with them.
 

[pachy-pleuro-whatnot-odon]

3 hours ago, sander said:

Wouldn't it be called a sacral vertebra then? I mean that is the area between dorsal and caudal vertebrae in other animals?

 

I haven't seen the term "sacral" applied to any derived marine reptile anatomy - i.e., ichthyosaurs, pl(es)iosaurs and mosasaurs - most likely because the term "sacral" would imply the vertebra being part of the sacrum, which these animals don't have. Rather, you'd refer to this area as "pelvic", thus "pelvic vertebra". However, Dean didn't mention anything about where along the gradient from dorsal to caudal vertebrae on the spine my vertebra could've come from, and my guess is this might be very species specific. In terrestrial animals you could use the term "lumbar" for this, to indicate a region along the spine slightly bigger than just the sacrum, but I don't think this term is applied to derived marine reptiles either. The most reasonable suggestion, therefore, I think, would be to describe the vertebra as a pelvic to initial caudal one.

 

4 hours ago, sander said:

And it is good to know that Dean is so friendly, I might show him a few of my possible ichthyosaur vertebrae too then sometime soon. Maybe he can help me with them.

 

Yeah, he's definitely a cool and helpful guy. He did, however, point out to me that he's not particularly versed in Triassic material. So if you're looking for identification of Triassic vertebrae vis-à-vis other Triassic animal species, I'm not sure whether he'd be able to help you much. But best to ask him yourself, of course. Or post them here. I'd be very interested in having a look at them, and there's definitely people on TFF much more familiar with the European Triassic than I am.

[sander]

At the moment I am still busy on my squalicorax collection, but when that is done i will probably focus on either Ichthyosaur, sauropterygians or Triassic cephalopods. Not sure yet what the next project will be haha. I might ask around here for some information too for that, but i think that i really need specialists to figure the stuff out that I can't sort out myself.

[Pemphix]

Shape, size, structure is typical for ichthyosaurs in the Muschelkalk. Unfortunately making a call for Genus or species is mostly difficult, as vertebras helding not much info for the determination.

Possible candidates: Shastasaurus, Opthalmosaurus, Cymbospondylus and probably Blezingeria (not an ichthyosaur).

I would ask Michael Maisch, as he has a lot of knowledge about ichthyosaurs:

https://www.researchgate.net/publication/260272778_Phylogeny_systematics_and_origin_of_the_Ichthyosauria-the_state_of_the_art

https://www.researchgate.net/publication/260287169_The_Ichthyosauria

https://www.researchgate.net/publication/230128086_The_mixosaurid_ichthyosaur_Contectopalatus_from_the_Middle_Triassic_of_the_German_Basin

https://www.tandfonline.com/doi/abs/10.1671/0272-4634(2006)26[598%3ATBOPNS]2.0.CO%3B2

 

[pachy-pleuro-whatnot-odon]

1 hour ago, Pemphix said:

Shape, size, structure is typical for ichthyosaurs in the Muschelkalk. Unfortunately making a call for Genus or species is mostly difficult, as vertebras helding not much info for the determination.

Possible candidates: Shastasaurus, Opthalmosaurus, Cymbospondylus and probably Blezingeria (not an ichthyosaur).

 

Yeah, I'm aware that it's unfortunately not really possible to identify ichthyosaur vertebrae as to genus or species. The reason for me posting his specimen here for identification all the same was that I had hoped the peculiar rib facets to be diagnostic in the way of may be being a trait relatable to a specific ichthyosaur (sub)family or genus. After having spoken to Dean Lomax, however, this does not appear to be the case. (I think you meant Omphalosaurus when you wrote Ophthalmosaurus, by the way, as the latter is a Middle Jurassic species )

 

 

1 hour ago, Pemphix said:

I would ask Michael Maisch, as he has a lot of knowledge about ichthyosaurs:

https://www.researchgate.net/publication/260272778_Phylogeny_systematics_and_origin_of_the_Ichthyosauria-the_state_of_the_art

https://www.researchgate.net/publication/260287169_The_Ichthyosauria

https://www.researchgate.net/publication/230128086_The_mixosaurid_ichthyosaur_Contectopalatus_from_the_Middle_Triassic_of_the_German_Basin

https://www.tandfonline.com/doi/abs/10.1671/0272-4634(2006)26[598%3ATBOPNS]2.0.CO%3B2

 

I have considered writing him before, but indeed didn't list him above. Although I think I already have my answer, I've still written him, as I suspect that as a German researcher he might be more familiar with the earlier stages of the Triassic, much less commonly exposed in the UK. So, lets see what comes out of that In any case, thanks for the suggestion!

 

[Pemphix]

On 7/13/2021 at 12:39 PM, pachy-pleuro-whatnot-odon said:

 

(I think you meant Omphalosaurus when you wrote Ophthalmosaurus, by the way, as the latter is a Middle Jurassic species )

Yes, indeed - thanks for the clarification..

 

...I've still written him, as I suspect that as a German researcher he might be more familiar with the earlier stages of the Triassic, much less commonly exposed in the UK.

He is a well known expert for ichtyosaurs of all stages. But yes, living in Germany giving him a special view on those species, so that would be always my first try...

 

 

[pachy-pleuro-whatnot-odon]

While I have yet to receive a response from Michael Maisch, @RuMert has just pointed me to a monograph on Ophthalmosaurus by Moon and Kirton (2016), that, as it turns out, illustrates exactly those transitional vertebrae with the merger between diapophyses and parapophyses into synapophysial rib facets that Dean Lomax described, thus reaffirming his conclusion (ibid., text figure 24):

 

dp = diapophysis; pp = parapophysis; sp = synapophysis

 

Interestingly, a similar merger takes place in cervical vertebrae, as illustrated in McGowan and Motani's (2003) "Handbook of Paleoherpetology, Part 8: Ichthyopterygia" figure 18, C-D. Note, however, that there does seem to be some generic variation at play here, since while this merger in the cervical vertebrae occurs in Ophthalmosaurus, it does not appear to do so in Ichthyosaurus communis (ibid.. A-B; although, admittedly, this could be positional, since only two such vertebrae are illustrated in the dorsal-to-caudal range for Ophthalmosaurus as well):

 

[pachy-pleuro-whatnot-odon]

Though neither specimen is of particularly high quality, I thought I'd illustrate the differences between the vertebrae of ichthyosauria and those of Blezingeria ichthyospondyla with a side-by-side comparison of two specimens from the quarry at Bettborn.

 

 

As you can see, not only is the B. ichthyospondyla vertebra taller than the ichthyosaurian one, it also has a thick bevelled edge, which makes the dive into the hourglass-shape much more gradual in ichthyosaurs, where the thickness of the vertebral centrum starts reducing from the very edge. Other noteworthy features are comparatively huge diapophyses on Blezingeria, as well as evidence of scarring on the dorsal side of the vertebra where the neural arch would've connected in Blezingeria, but not in ichthyosaurians. Below are some further photographs of the Blezingeria ichthyospondyla vertebra, which can be compared with the ichthyosaurian one from the beginning of this thread: