Marine reptile teeth from Nancy

[pachy-pleuro-whatnot-odon]

Hi everyone,

 

I got offered this pair of marine reptile teeth as those of ichthyosaurs, but am having a hard time making my mind up about their identification. I'd therefore like to ask for your opinions.

 

 

The teeth were found during works around Nancy back in 2004, and, based on other ichthyosaur finds from the region, likely dates the Toarcian stage of the Early Jurassic (though, from what I can tell, Oxfordian marine deposits are also accessible in the area). This makes them roughly the same age as material from the Posidonia Shale/Holzmaden and Whitby, but slightly younger than that of the Lyme Bay area. The above photograph is the only one I have, with the seller being on fieldwork and unable to provide much further information for the next couple of weeks.

 

Although we can safely eliminate marine crocodile as contenders for the original owners of these teeth, and I think they are too big to have belonged to fish, I'm undecided on whether these are just highly worn ichthyosaur teeth or plesiosaur teeth. There's something to be said for both. The tall, slender shape of the teeth and their slight curvature, for instance, would seem to fit plesiosaurian teeth, as would, most significantly, the round root of the bigger tooth. In that case, however, the smaller tooth does seem a bit stubby, and the traces of ornamentation along the midsection of the larger tooth surprisingly equidistantly spaced.

 

Generally, the morphology of the smaller tooth to me suggests ichthyosaur rather than plesiosaur. But if that were the case, I'd expect either enamel folds on the crowns themselves, folds on the root, or both (even when ichthyosaur teeth have smooth enamel, I find they still have folds on their roots). I'd also expect the root to be more polygonal in shape, somewhere in the range of triangular to (rounded) square. This is not the case. Now there seems to be some ornamentation midway up the larger specimen which equidistant spacing correlates well with patterns of the folds found on ichthyosaur teeth, thus may indicate the tooth is ophthalmosaurid and therefore Oxfordian rather than Torcian in age. The below image I drew up makes the comparison:

 

 

As you can see, the match is less then ideal, as the top part of the French tooth is completely devoid of enamel folds, whereas in an ophthalmosaurid tooth the plicidentine folds actually taper out until the enamel is clear. @belemniten, however, posted images of a couple of his ichthyosaur teeth from Holzmaden, one of which appears to show a similar pattern as visible in the middle of the French tooth under consideration here, including what appears to be a round root:

 

 

However, when looking at other images of the same tooth, it turns out that the root does have folds, as you'd expect from ichthyosaur teeth:

 

 

Similarly, the below tooth seems to have a superficially similar appearance to the French tooth for the hairline cracking of the enamel, and the fact that enamel appears to be missing from the crown immediately above the root proper (which, again, exhibits folds, however). Still, if the "smooth round root" on the French tooth would've been covered by enamel as well, this would make for a very tall tooth as far as ichthyosaurs go.

 

 

As illustrated by the specimen below (source), though, ichthyosaur teeth do occasionally have round roots:

 

 

Moreover, the folds on the root don't always run the full height of it (image source):

 

 

Lastly, as the specimen below demonstrates (source), the entire root can look completely smooth, presumably from wear:

 

 

As such, I'm wondering whether the French tooth specimen might not be a very worn ichthyosaur tooth, with its parts being composed as such:

 

 

This doesn't particularly make too much sense to me either, as the part of the root with folds is rather long and has a very abrupt transition into the remainder of the root. In addition, it raises the question of how the tooth would've gotten so worn. Though I understand there are fluvially exposed sites around Nancy, could this have caused the wear we're seeing. Or would the wear rather be peridepositional?

 

So, I guess I can summarize my questions as:

1. Do these look like plesiosaur or ichthyosaur teeth?
   1. If plesiosaurian, what would the equidistant striations on the midsection of the tooth be?
   2. If ichthyosaurian, do these teeth look more ophthalmosaurid or pre-ophthalmosaur? How might the wear I think I'm seeing be explained?

 

Thanks for the help!

 

cc @paulgdls @PointyKnight @DE&i @Welsh Wizard @RuMert @FF7_Yuffie

Edited May 23, 2021 by pachy-pleuro-whatnot-odon

[pachy-pleuro-whatnot-odon]

For comparison, here are some further pictures of a small ichthyosaur tooth from Lyme Regis:

 

 

 

And plesiosaur tooth, also from Lyme Regis:

 

[PointyKnight]

Hard to tell from these photos, but I agree that the smaller tooth looks very ichthyosaurian. I think it's a bit early to exclude marine crocs entirely - certain teeth can resemble some plesiosaurs quite closely, which is where having other aspect views of these teeth would come in helpful. An indeterminate ichthyosaurid and 'Steneosaurus'-type teeth are described from the Toarcian of Nancy, apparently Sinemurian exposures exist as well (though Toarcian seems to be the most prominent). Plesiosaurs aren't described, but certainly existed. It's important to keep in mind how fissures in the enamel can superficially resemble faceting or worn striations. I'd hold back on a definite ID before there's better pictures.

[RuMert]

Too blurry pics IMHO. But probably ichthyosaurs.

Those comparison pics are also too small (cannot be enlarged)

Edited May 23, 2021 by RuMert

[pachy-pleuro-whatnot-odon]

18 minutes ago, RuMert said:

Too blurry pics IMHO. But probably ichthyosaurs.

Those comparison pics are also too small (cannot be enlarged)

 

Yeah, I know. Sorry about that! They were a bit bigger when I grabbed them off of Google, but that's because Google scales all images in its search results. I had hoped for better comparison photographs, but this was all I could find to illustrate my points, as these features are far from typical. Which is actually one of the issues I have explaining the larger tooth as a worn ichthyosaur, since it seems unlikely to me that all types of wear, normally seen individually (if at all), would combine on this one tooth like this.

 

Let's see, but may be I just need to wait for the seller to be back out of the field, so that they can take clearer photographs...

 

In any case, as soon as I mentioned my reservations as to the teeth being ichthyosaurian to him, the story changed to the teeth being plesiosaurian. Not a good sign... 

Edited May 23, 2021 by pachy-pleuro-whatnot-odon

[pachy-pleuro-whatnot-odon]

2 hours ago, PointyKnight said:

Hard to tell from these photos, but I agree that the smaller tooth looks very ichthyosaurian. I think it's a bit early to exclude marine crocs entirely - certain teeth can resemble some plesiosaurs quite closely, which is where having other aspect views of these teeth would come in helpful. An indeterminate ichthyosaurid and 'Steneosaurus'-type teeth are described from the Toarcian of Nancy[.]

 

Yeah, the small tooth is the one I have least doubts about being an ichthyosaur, albeit a fairly uninteresting one. However, the shape clearly matches my expectations for such a tooth.

 

As to the tooth being a marine crocodile, you're right in that there's a possibility that these teeth still belong to one or more species of thalattosuchian. However, in that case, I'd expect to see the carinae that each of the species known to me have, be it metriorhynchid, teolosaurid or machimosaurid. Unless utterly and completely worn away - which I don't believe to be the case, at least not to the extent of eradicating all traces - I think the carinae should be visible, as the smaller tooth seems to be presented lingually and the larger is presented mesiodistally (i.e., should show up on the larger tooth irrespectively, and the shape of the tip of the smaller should hint at carinae if these are present there). Also, I've already got a pair of Steneosaurus-teeth from around Nancy (sold as ichthyosaur), that I've tentatively classed as S. megistorhynchus - now Seldsienean megistorhychus - based on their morphology, as described here and in the figure from Mueller-Töwe (2006) below.

 

 

Of course, with this species being so rare - that is, assuming my identification is correct - there are bound to be other Steneosaurus-species in the area. But the point is, I think these would stand out sufficiently...

 

5 hours ago, PointyKnight said:

[A]pparently Sinemurian exposures exist as well (though Toarcian seems to be the most prominent). Plesiosaurs aren't described, but certainly existed.

 

The information you found on the Sinemurian being exposed in the region and the lack of described plesiosaurs is interesting. I hadn't come across these details myself yet, and may decrease the likelihood of the teeth belonging to plesiosaurians, while increasing the comparability with the faunal assemblage of Lyme Regis. This may, ironically, make it easier to identify plesiosaurian teeth, if such they are, as I have Sinemurian specimens, but it's proven impossible for me to find any confirmed Toarcian reference material.

 

In any case, I guess I really should get more confirmation about the age of the teeth...

 

5 hours ago, PointyKnight said:

It's important to keep in mind how fissures in the enamel can superficially resemble faceting or worn striations. I'd hold back on a definite ID before there's better pictures.

 

Although I'm aware of that, and would certainly agree with your advice for caution in particular reference to the fissures exhibited in the Holzmaden-specimens I included in my initial post, the markings on the larger tooth, even though seen from a blurry photograph, seem very straight and regularly spaced. Too much so, in my opinion, to be merely coincidence. However, I will see if I can get some additional - and primarily better quality - photographs. May be they'll clear things up a bit.

 

In any case, thanks for your help! As always, very useful information!

[pachy-pleuro-whatnot-odon]

I finally received some additional photographs. Unfortunately, though, the image revolution is still pretty low, as is the image quality (actually, I had to boost the colours in the photographs a bit for more details to stand out):

 

 

I've since spoken to a palaeontologist from the Nancy-area who, even based on the original photograph was able to confirm that these are indeed ichthyosaur teeth, more specifically of the genus Eurhinosaurus. For while hard to see in the photographs of these specimens, they do appear to exhibit the horizontal banding and construction near the apex as is typical for that genus (compared with the photograph below):

 

 

And here's another specimen, taken from the Steinkern-community:

 

Edited July 2, 2021 by pachy-pleuro-whatnot-odon
Image formatting

[pachy-pleuro-whatnot-odon]

So the teeth came in day before yesterday, and while I must say that it's particularly hard to make out the hallmark characters that define an Eurhinosaurus sp. tooth on these specimens , that's definitely what they are. However, as it turns out, not all features have to be present in equal measures. The smaller tip, for instance, though generally being rather smooth and featureless, exhibits some hard to spot horizontal banding only present in colour, whereas I was unable to make out any type of banding on the larger specimen. The latter, however, has very fine, equidistantly spaced striations on the lower part of the tooth crown that at first threw me off but are actually present on the specimen reposted from the Steinkern-community above as well. Thus, I was able to identify the tooth primarily based on this feature.

 

Then, as if by divine providence, as I went over a certain part of my collection, I bumped into a tooth from Lyme Regis that I had bought as an indeterminate plesiosaur, and spotted traces of a root with folds on it. In other words, this tooth was not plesiosaurian at all, but instead one, very similar in morphology to Eurhinosaurus, including the horizontal banding! The problem is, though, that the deposits at Lyme Regis are Sinemurian in age, a time during which Eurhinosaurus had not evolved yet. A similar genus, Excalibosaurus, was around at this time, however, and as per the preview (I'm unfortunately unable to access paywalled articles) of McGowan's (2003) "A New Specimen of Excalibosaurus from the English Lower Jurassic" "Maisch and Matzke (2000:86) [...] synonymized Excalibosaurus with Eurhinosaurus on the grounds that 'apart from the differences in the extent of the overbite, there are no fundamental distinguishing features'". This being the case, I think we can safely assume the teeth of Excalibosaurus to have a similar morphology to those of Eurhinosaurus, thereby allowing me to identify the tooth I rediscovered in my collection as Excalibosaurus, an apparently rare genus of ichthyosaur, and one not listed in Christian's excellent listing of marine reptile species known to occur at Lyme Regis.