Pliosaur tooth, or ophthalmosaurid ichthyosaur (Stary Oskol)

[pachy-pleuro-whatnot-odon]

Hi all,

 

First off, this is not my fossil (though I own a large crow of similar morphology), but one I recently bumped into and found particularly curious. Why? Because it's morphology seems to contradict itself. Described as a Polyptychodon interuptus (no longer considered a valid genus; Madzia [2016]) from the Late Jurassic Volga Beds (?) of Stary Oskol, the tooth appears to have enamel folds consistent with what one might expect from an ophthalmosaurid ichthyosaur, such as Platypterygius sp.. The root, however, is smooth and round, with a hollow base, which, unlike the rectangular and "fibrous" roots more typical of ophthalmosaurid ichthyosaurs, is more indicative of pliosaur. Here are some pictures of the tooth. Unfortunately, as it was sold off by auction back in 2017, there's no chance of getting any better quality photographs:

 

 

I know the seller is quite familiar with pliosaur teeth, so would be surprised if they identified the tooth wrongly. The ornamentation on the tooth, however, bugs me as not matching what I would expect for pliosaur, especially a brachauchenine species. Below are a schematics illustrating various tooth crown ornamentations amongst marine reptiles (figure 2 from McCurry et al. [2019]) and some examples of British brachauchenine pliosaur teeth (figures 3, 4, 5 and 6 from Madzia [2016]) for comparison.

 

 

Tooth ornamentation in marine reptiles: A. Deinosuchus rugosus; B. Spinosaurus; C. Ichthyosaurus; D. Pliosauridae indet.; E. Globidens alabamensis; F. Hydrurga leptonyx; G. Mammalodontidae indet.

 

 

 

Here's the only confirmed Stary Oskol pliosaur tooth I've been able to find as a reference for how the above translates to that location (source):

 

 

And, finally, for completeness, some Stary Oskol platypterygiine ichthyosaur teeth:

 

 

My questions to you are:

1. Does this look like an ichthyosaur or pliosaur tooth to you, and why?
2. I've heard, by word of mouth (i.e., got from a source that's not academic), that certain late ophthalmosaurid species developed root tooth roots. Can anybody confirm or deny this, if possible with academic reference?

 

Thanks for your help!

 

@RuMert @Anomotodon @paulgdls @PointyKnight @Mike from North Queensland @-Andy-

[Anomotodon]

I agree with you that enamel ornamentation is more consistent with ophtalmosaurid teeth. I am also not familiar with Jurassic deposits around Stary Oskol, I believe it's primarily Albian, which would make it a platypterygiine. As for the hollow roots - ichthyosaurs can have them sometimes, I believe due to damage during fossilization. Here is a rooted tooth I had that has a hollow root. Root shape also could be due to positional variation.

 

[pachy-pleuro-whatnot-odon]

19 minutes ago, Anomotodon said:

I agree with you that enamel ornamentation is more consistent with ophtalmosaurid teeth. I am also not familiar with Jurassic deposits around Stary Oskol, I believe it's primarily Albian, which would make it a platypterygiine. As for the hollow roots - ichthyosaurs can have them sometimes, I believe due to damage during fossilization. Here is a rooted tooth I had that has a hollow root. Root shape also could be due to positional variation.

 

Hi Tim,

 

Thanks for the quick response! Yeah, that's what I thought. But the round and smooth root is really odd. Of course, ophthalmosaur teeth have a smooth and round transitional "neck" region, but I doubt that argument could be used to explain away the smoothness of the root in this case. May be it could be an ophthalmosaurid tooth crown attached to a pliosaur tooth root? Then again, I don't really see any signs of where the two would have been connected, if this were the case...

 

As to the root of your ophthalmosaurid tooth being hollow (nice specimen, by the way! ), this is actually quite common. As @Mike from North Queensland explains here, this is due to a replacement tooth erupting below the tooth with the hollowed out root, and the root of the upper tooth being resorbed - one imagines much like is the case with mosasaur tooth replacement.

 

The problem is, though, that this hardly ever happens exactly in the middle of the upper tooth, thus rarely leaving such a perfectly round, walled cavity in the root of the upper tooth. In pliosaurs this is a much more common occurrence.

[RuMert]

I'm not a specialist on Stary Oskol material but this tooth looks to have separate enamel ridges so I'd agree with pliosaur. Albian-Cenomanian

[pachy-pleuro-whatnot-odon]

4 hours ago, RuMert said:

I'm not a specialist on Stary Oskol material but this tooth looks to have separate enamel ridges so I'd agree with pliosaur. Albian-Cenomanian

 

Yeah, that's what I thought. Late Jurassic indeed didn't seem quite right...

 

Anyway, you'd say then that irrespective of the round cross-section of the striae, which are atypical for pliosaurs (see image below, figure 4 from McCurry et al. [2019]), it's the separation between them that makes this a pliosaur tooth?

 

A. Polyptycodon interruptus; B. Globidens alabamensis; C. Goniopholis crassidens; D. Spinosaurus aegyptiacus; E. Ichthyosaurus communis; F. Zygorhiza kochii

 

That's interesting, as I've used exactly the same reasoning to declare my own specimen pliosaur rather than ichthyosaur. In fact, at points, there's more separation between the individual striae on my tooth than there is in the specimen posted above. However, in my specimen the striae don't run the full length of the crown, all terminating at the same height, much like in regular ophthalmosaurid teeth - all, except for in one spot, where occupational wear seems to have eroded some of the striations. A befriended palaeontologist therefore suggested that the morphological deviations I'm seeing in my tooth could be due to its size. In that respect it's unfortunate that the apex is missing from the specimen posted above - although it looks like the striae would've continued all the way to the apex in that tooth...

 

Anyway, I'll see if I can post some photographs of my tooth tonight, for comparison, if I can find some time...

[Anomotodon]

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

As to the root of your ophthalmosaurid tooth being hollow (nice specimen, by the way! ), this is actually quite common. As @Mike from North Queensland explains here, this is due to a replacement tooth erupting below the tooth with the hollowed out root, and the root of the upper tooth being resorbed - one imagines much like is the case with mosasaur tooth replacement.

 

The problem is, though, that this hardly ever happens exactly in the middle of the upper tooth, thus rarely leaving such a perfectly round, walled cavity in the root of the upper tooth. In pliosaurs this is a much more common occurrence.

 

Heh, in a week or so you'll like that tooth even more 

 

Actually found a paper about tooth histology in ichthyosaurs. It seems that the pulp cavity can get quite large and is centrally positioned in fully mature teeth. I guess the depression at the base of the root in other ichthyosaurs is characteristic of younger teeth at a stage when the replacement tooth just started growing and expands into a resorption pit connecting to the pulpar cavity (see pics below). And the very base could have been eroded, exposing the whole structure.

 

As for the root cross-section, here is a quote from this article. At least Aegirosaurus possessed an oval root outline, although other studies mentioned here state that late Cretaceous platypterygiines had a quadrangular root as you mentioned. I am not sure what this implies in the context of this thread, assuming the tooth in question is indeed from Stary Oskol and Albian, - but at least it shows that there is variation in this trait among platypterygiines (Aegirosaurus is a platypterygiine).

 

Quote

Bardet (1990), who analysed characteristic dental cross-sections, indicated that a circular shape of the crown and a quadrangular outline in the lower part of the tooth root apparently unites all Cretaceous ichthyosaurs. Later, Maxwell and Caldwell (2006) noted that not only the Cretaceous Platypterygius and Maiaspondylus possess this character, but also the Upper Jurassic Brachypterygius, whereas the character state remained unknown in the Upper Jurassic Aegirosaurus. Given the fact that the series of transverse sections can be referred to Aegirosaurus leptospondylus (sensu Bardet and Fernández 2000), this character can also be addressed in the serial transverse sections on slides 1–7 and the longitudinal section of slide “8”: the sections indicate that, while the crown has a circular outline, the root of the sectioned tooth did not have a quadrangular but an oval outline.

 

See b - Nannopterygius

 

 

Aegirosaurus (left)

 

 

Just the illustration of the depression I was talking about on one of my specimens

 

 

Edited July 27, 2021 by Anomotodon

[RuMert]

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

it's the separation between them that makes this a pliosaur tooth?

I believe those of ichthyosaurs are more thick than far from each other, in your example the other way round. Here's a tooth of mine, it looks almost like corduroy due to the number and thickness of ridges, while in pliosaurs the latter are rarer

Edited July 27, 2021 by RuMert

[Mike from North Queensland]

A photo direct into the base would tell a lot. From photos I would only guess pliosaur tooth crown with heavy restoration done around the root to make good a damaged section or to add a root to the tooth. That could also be the reason the tooth has a very central void for a replacement tooth. 

Remember Photos only tell (show) so much.

[pachy-pleuro-whatnot-odon]

@Anomotodon, let me respond to you a bit later. I'm not quite sure I get what you're saying yet...

 

On 7/28/2021 at 12:41 AM, Mike from North Queensland said:

A photo direct into the base would tell a lot. From photos I would only guess pliosaur tooth crown with heavy restoration done around the root to make good a damaged section or to add a root to the tooth. That could also be the reason the tooth has a very central void for a replacement tooth. 

Remember Photos only tell (show) so much.

 

I agree more and better photographs would be needed to properly identify this piece, but those simply aren't available (which may be the reason the youth sold for comparatively little). Personally, I don't see too much evidence for the root having been extended, though. In any case, for you the ornamentation on the crown would be consistent with pliosaur then, I take it? At least insofar as can be made out from the photographs... I would agree, if it weren't for the broad and rounded striations visible in the last photograph, which seem much more blunted than what I'd expect a pliosaur to have...

 

On 7/27/2021 at 5:57 PM, RuMert said:

I believe those of ichthyosaurs are more thick than far from each other, in your example the other way round. Here's a tooth of mine, it looks almost like corduroy due to the number and thickness of ridges, while in pliosaurs the latter are rarer

 

Beautiful ichthyosaur tooth! Though not unambiguously identifiable as ichthyosaurian in this photograph, in my opinion, it is undeniably ophthalmosaurid in the other photographs found here.

 

Yeah, that's what I thought: that the ornamentation on ichthyosaur teeth is much more rounded and thicker than that of pliosaurs, giving the striae of a pliosaur tooth a much crisper/sharper appearance than those of ichthyosaurs, which have an overall blunted and denser look...

 

What makes the tooth in my original post so weird, at least to me, is that its ornamentation exactly appears as round and blunted as in ichthyosaurs, but neither root nor the striae that seem to reach the full apicobasal height of the tooth match that supposition...

 

In that light, here's the other specimen I've mentioned a couple of times above, and that I'm unsure about whether to class as ichthyosaur or pliosaur. The seller I got it from was convinced it's a pliosaur, but the photographs he showed me made me think it's an ichthyosaur for the nature of its thick round striations and the fact that they seem to terminate equidistant below the apex. When I got the tooth, however, the apex appeared too worn to say much about continuation of the striae in this area, and they moreover have a discontinuous character, which now to me suggests pliosaur. But I'm just not sure... As said before, a befriended palaeontologist proposed that the traits that make me wonder about a possible pliosaurian nature of the tooth could, in fact, be either pathologies (an area devoid of situations before the start of the enamel peel near the apex, for instance, is clearly due to occlusional damage) or simply deviations caused by the large size of the tooth. All opinions welcome

 

 

[RuMert]

1 hour ago, pachy-pleuro-whatnot-odon said:

at least to me, is that its ornamentation exactly appears as round and blunted as in ichthyosaurs

That's what I thought initially, but separate ridges are visible in the 3rd pic and their different length in the 2nd. So it looks something along the lines of those texan pliosaur teeth we've discussed recently

[pachy-pleuro-whatnot-odon]

3 hours ago, RuMert said:

That's what I thought initially, but separate ridges are visible in the 3rd pic and their different length in the 2nd. So it looks something along the lines of those texan pliosaur teeth we've discussed recently

 

Yeah, I agree that the third photograph shows clear signs of separation of the striae - this is, in fact, one of the main reasons for me to consider my specimen pliosaurian after all - but think the evidence of not all striations reaching the tooth apex/not all striae reaching the same height is a bit low in the second photograph, where I can only spot one such instance and the lefthand side appears too damaged for any inferences to be made. Still, I agree that between 1. the separation of striations; 2. not all striae terminating at the same height; 3. the suggestion that most striae reach the tooth apex; and 4. the smooth round root, this does appear to be a pliosaur tooth. Even if the type of striations doesn't strike me as typical, even if the Texas teeth you mentioned (throwing one from a different Texan location in for good measure):

 

 

However, if we accept that at Stary Oskol pliosaur teeth can, as it appears, have more rounded and blunt striations, this raises the question if my specimen is one too. The separation of striae would suggest that it is, though it's impossible to determine whether any striations would've reached the tooth apex, as that part of the enamel is simply too damaged. I haven't, however, as I recall (I'm abroad right now), seen any striations terminated before the rest - which would indeed have closed the case for me too.

 

I guess the question now is: of the four features listed above, how any are needed to positively identify a tooth as pliosaurian?

[pachy-pleuro-whatnot-odon]

On 7/27/2021 at 2:21 PM, Anomotodon said:

Heh, in a week or so you'll like that tooth even more 

 

I'm hoping it will arrive tomorrow, but you never know around here... In any case, it's arrived in France today, it just needs to find its way here from Paris

 

Quote

Actually found a paper about tooth histology in ichthyosaurs.

 

That's a very interesting article. Thank you! What surprised me most about the description given in it was that the ornamentation on the tooth was only apparent in the two slices taken from the tooth following the one slice closest to the top (i.e., 2nd and 3rd slices, or a2 and a3 in the image), with all further slices being devoid of ornamentation. In this respect it's a pity we don't have any illustrations of how the tooth would've looked whole, to see why there is no ornamentation further down. Especially since no mention is made of acellular cementum in any of the lower slices either, up till the very last of them, whereas the longitudinal section suggests that acellular cementum may normally cover up that portion of the orthodentine not protected by the tooth enamel. Then again, the below specimen also appears to have exposed orthodentine visible between the ornamented tooth enamel and underlying cementum. It's possible the tooth Bauer analysed exhibited the same condition. In any case, it seems like the orthodentine doesn't always need to be fully covered by cementum...

 

 

Another instance of this same condition is the below example, where, however, the orthodentine itself seems to bear ornamentation and form the neck.

 

 

Equally interesting was the fact that the tooth was apparently affected by microscopic boring organisms while the tooth was still in use by the ichthyosaur...

 

Mycelites ossifragus borings affecting an ophthalmosaurid ichthyosaur tooth (extracted from figure 3 from Scheyer and Moser, 2011)

 

Quote

It seems that the pulp cavity can get quite large and is centrally positioned in fully mature teeth. I guess the depression at the base of the root in other ichthyosaurs is characteristic of younger teeth at a stage when the replacement tooth just started growing and expands into a resorption pit connecting to the pulpar cavity (see pics below). And the very base could have been eroded, exposing the whole structure.

Yeah, I agree. I would indeed say that when a replacement tooth starts growing it starts creating a resorption pit, which will continue to grow along with the replacement tooth, all the while "eating away" at the cellular cementum towards the pulpar cavity. If the tooth in use for some reason gets detached before the replacement tooth breaks through the cellular cementum, it's likely to leave just a depression. However, if it manages to break through to a significant enough an extent, it may actually expose the pulp to erosion, leaving us with hollowed out tooth roots.

 

AC = acellular cementum, CC = cellular cementum, DT = dentine tubules, GT = granular layer of Tomes, OD = orthodentine, P = pulp cavity, SC = sparitic calcite, ShF = Sharpey's Fibres (figure 6 from Scheyer and Moser, 2011)

 

Quote

As for the root cross-section, here is a quote from this article. At least Aegirosaurus possessed an oval root outline, although other studies mentioned here state that late Cretaceous platypterygiines had a quadrangular root as you mentioned. I am not sure what this implies in the context of this thread, assuming the tooth in question is indeed from Stary Oskol and Albian, - but at least it shows that there is variation in this trait among platypterygiines (Aegirosaurus is a platypterygiine).

 

Actually, this is the part of the authors' conclusions I'm least convinced by. For, while they mention an oval root shape, I wonder how they were able to determine this from a longitudinal thin section (which, as I understand it, is all they have left of this one specific tooth). Possibly, they are referring to the longitudinal/vertical shape of the root, which may very well be oval in appearance. My suspicion, however, is that when Bardet, Maxwell and Caldwell described Cretaceous ichthyosaurs as all having quadrangular tooth roots, they intended this to mean the horizontal cross-section, rather than the vertical one. If the latter is what Scheyer and Moser refer to, though, than they are simply comparing apples with pears and their conclusion is unfounded. Yet, as I haven't read either Bardet or Maxwell and Caldwell, I can't say whether this is the case with any certainty.

 

All the same, I do think the article illustrates that the root structure of ophthalmosaurid teeth is succinctly distinct from that of the tooth I originally posted above. Thanks again for sharing, a very useful resource!

Edited August 1, 2021 by pachy-pleuro-whatnot-odon

[pachy-pleuro-whatnot-odon]

Just for fun, as we were discussing resorption pits in ichthyosaur teeth, and have, up to now, mainly been talking about more derived parvipelvian ichthyosaurs, here's an example of a resorption pit on the root of the tooth of a Stenopterygius sp. from Holzmaden:

 

Edited August 4, 2021 by pachy-pleuro-whatnot-odon
Made image larger

[pachy-pleuro-whatnot-odon]

On 7/31/2021 at 4:14 PM, pachy-pleuro-whatnot-odon said:

 

On 7/31/2021 at 10:09 PM, pachy-pleuro-whatnot-odon said:

However, if we accept that at Stary Oskol pliosaur teeth can, as it appears, have more rounded and blunt striations, this raises the question if my specimen is one too. The separation of striae would suggest that it is, though it's impossible to determine whether any striations would've reached the tooth apex, as that part of the enamel is simply too damaged. I haven't, however, as I recall (I'm abroad right now), seen any striations terminated before the rest - which would indeed have closed the case for me too.

 

I have decided to go for brachauchenine pliosaur for the above tooth from my collection, by the way, although not for the spacing between the striations and obviously not for their rounded shape. For, as can be seen in the below indeterminate ophthalmosaurid tooth (taken from figure 15 from Fischer, Bardet, Guiomar and Godefroit [2014]) the striae on ichthyosaur teeth may, in fact, be quite distantly spaced from one another (although it is unclear if this affects distribution around the circumference of the tooth equally). However, I had another look at the tooth under clear magnification. And while worn off, remnants of striations remain clearly visible up to the very apex of the tooth. Together with the variation in spacing of striations and the fact that pliosaur teeth from Stary Oskol can, apparently, have very rounded striae (thus negating the ichthyosaurian identification), this now has me convinced...