Kimmeridgian Clay alligatoroid or Oxford Clay pliosaur tooth

[pachy-pleuro-whatnot-odon]

Hi everyone,

 

I recently bought this tooth on a whim. It was described as Diplocynodon sp. from the Kimmeridge Clay and reworked into the Albian-age Faringdon Sponge Gravels at the Wicklesham Pit.

 

 

 

 

However, this description is obviously wrong in either species attribution or locality, since Diplocynodon is an alligatoroid genus dating to the Paleocene to middle Miocene, and could therefore not possibly have been found in the Sponge Gravels as Wicklesham Pit. Going by the label that came with the tooth, however, the seller whom I bought the tooth from just copied the information on the label provided by the person they bought the tooth from (I think I recognize the labelling-style, which means I may have a lead to trace the provenance - although that would very much depend on how long records are kept by that other seller and on how long ago the tooth left them).

 

As the tooth isn't rolled, as much of the material form the Sponge Gravels is, and in preservation also doesn't match the buff through orange to deep red colours of most other Kimmeridge Clay material I've seen - whether from Faringdon or elsewhere (mainly Abingdon) - I'm pretty confident this tooth doesn't come from the reworked deposits at Wicklesham Pit. Rather, the state of preservation reminds me of finds from the Oxford Clay. In fact, the root of the tooth has some black deposit on it, that I take to be oxidized pyrite - something I've learned from this thread to be a not uncommon feature of Oxford Clay fossils.

 

Another option as to the tooth's origin is that the tooth could come from Hamstead on the Isle of Wight, where Diplocynodon is known to occur. The dark/black colouration of the tooth and traces of what appears to have been buff-coloured matrix - as opposed to the light grey one of the Oxford Clay - may point in that direction. Though I consider this possibility less likely than the Oxford Clay one for the reasons set out below.

 

Turning to morphology, the tooth doesn't seem to quite match examples of Diplocynodon I've been able to find online. For, while my tooth is densely ornamented with strong striations and exhibits - as far as I can make out - only one possible carina ("possible", as it may just be an apicobasal ridge), other teeth I've seen are mostly smooth/unornamented with what look to be two carinae (although alligatoroid teeth can have anywhere from zero through two carinae and I've also been able to find at least one Diplocynodon-tooth specimen with striations). Moreover, my tooth is conical, which at least rules out the more robust "short but wide" Diplocynodon morphotype.

 

Diplocynodon hantoniensis teeth, Lower Hamstead Beds , Hamstead, Isle of Wight (source)

 

 

 

 

 

 

 

 

 

 

 

Diplocynodon sp. teeh from the Faluns of Touraine, region of Savigné (source)

 

 

 

 

 

 

 

 

 

Diplocynodon hantoniensis from the Eocene deposits at Barton, Hampshire; note the striations

 

 

 

 

 

 

 

 

 

 

 

 

This brings us to a closer examination of the features of the tooth's ornamentation, as seen under a microscope. Visible are not just the black deposit on the root and strong and dense striations referred to above, but also what I make out to be remnants of the fossil's original yellow matrix; reticulation of striae; striations stopping close to the base of the tooth, rather than reaching the full apicobasal height; the overall texture of the enamel in between of the striae; and partial cross-section through the tooth enamel.

 

 

 

In particular with respect to the cross-section, it may be useful to have a look at the below illustration, figure 4 from McCurry et al. (2019). For, of course it could just be my imagination, but I see greatest similarity with specimen A - that is, the brachauchenine tooth marked as P. interruptus (but see here for a discussion on the validity of this species).

 

Cross-sections through the teeth of A. Polyptycodon interruptus, B. Globidens alabamensis, C. Goniopholis crassidens, D. Spinosaurus aegyptiacus, E. Ichthyosaurus communis, F. Zygorhiza kochii

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Similarly, if I look at the below diagram of dental ornamentation amongst various clades of marine animal (figure 2, ibid.), I find greatest semblance with tooth D, sauopterygia, pliosauridae indet. (although an argument could be made for A, crocodylomorpha, Deinosuchus rugosus, could be made as well).

 

Phylogenetic distribution and morphological similarity of apicobasal ridges: A. Deinosuchus rugosus; B. Spinosaurus; C. Ichthyosaurus; D. Pliosauridae indet.; E. Globidens alabamensis; F. Hydrurga leptonyx; G. Mammalodontidae indet.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I see further comparability in ornamentation when looking at images of the below tooth:

 

 

As such, I believe that the tooth under discussion here is, in fact, a pliosaur tooth from the Oxford Clay. Moreover, seeing as the density of the striae all round and smooth enamel surface in between, I'm thinking the tooth might belong to Simolestes vorax. However, the traces of yellow matrix make me wonder whether the tooth indeed derives from the Oxford Clay, whereas the few vermiculations visible at the base of the tooth - rare on S. vorax - and the tooth's overall colour make me hesitant whether this might not actually be a Liopleurodon ferox (although I'd think the density of striations would be quite high, in that case; but for comparison with another small L. ferox tooth, see here).

 

As it stands, I guess my questions are:

1. Are the traces of yellow I'm seeing on the tooth indeed remnants of matrix, or could they be dried up glue?
2. Where was the tooth found, what deposits does it derive from? Did it indeed come out for the Kimmeridge Clay, or did it come from either Oxford Clay or Hamstead Beds? Does this correlate with the traces of matrix seen on the tooth?
3. Considering the geological origin of the tooth, is it more likely to be crocodilian or pliosaurian?
4. Is the species attribution correct? That is, if crocodilian, is this indeed a Diplocynodon tooth? And if it were pliosaurian, does it belong to S. vorax or L. ferox?

 

Thanks for your help!

 

@paulgdls @PointyKnight @DE&i @RuMert @Jesuslover340 @caterpillar

Edited May 4, 2021 by pachy-pleuro-whatnot-odon

[PointyKnight]

Hey Alexander!

1. Looking at the traces all over the tooth, I think this is remaining matrix.

2. This looks a lot like fossils I've seen come from the Faringdon Sand that Kimmeridge Clay fossil are usually reworked into like you mentioned. I do not believe this is from the Oxford Clay, since even though Wicklesham is deeper than Faringdon Pit, the OC is still very deep underground in these localities. Exposures are usually Gault Clay and Lower Greensand [like Faringdon Sponge Gravel member], which would explain the given locality.

3/4. I don't believe this is pliosaurian, since the striae appear to reticulate basally, something I don't know if any pliosaurs do. It does however look very much machimosaurid to me. I don't think there's any machimosaurid taxa described past the Barremian, but I seem to remember their record, while spotty, extends beyond that. Alternatively, it might bear some resemblance to certain polycotylid teeth, but more so to those of Late Cretaceous polycotylids. I think croc might be the better guess.

Edited May 4, 2021 by PointyKnight

[caterpillar]

One thing is certain, it is not Diplocynodon

[caterpillar]

And I don't think it's croc

[pachy-pleuro-whatnot-odon]

Thanks, guys! Lets wait for some others to chime in and see what they think. Your points about the matrix and stratification at Wicklesham are very instructive, Mien! However, I'm inclined to keep an open mind as to whether or not the tooth came from Wicklesham in the first place. Though, if the matrix matches, as you said, than this does strengthen the argument for this being the case. I don't think the tooth is machimosaurid, though, as I've got a couple of Oxford Clay specimens (will post pictures later), and they are quite dissimilar. Also, I think I would've recognized this as Machimosaurus sp. if, indeed, that's what it is...

[PointyKnight]

Absolutely! My guess is, since this seller usually has a lot of Kimmeridge Clay material reworked into the Greensand, any material gets marked as reworked, even when it may not be. Looking through YOUNG et al. 2014, short, branching apical reticulations like the one in the second close up [can't seem to quote these individually] are indeed a thing in Machimosaurus. Though I wouldn't suggest it to be actually Machimosaurus itself, maybe more of a Machimosauridae indet., which would fit well with the overall shape, striation pattern and density IMO.

Edited May 4, 2021 by PointyKnight

[pachy-pleuro-whatnot-odon]

Hi Mien,

I've had a quick glance-over of Young et al. (2014) and must say it looks like a very interesting article. I'll have a see if I can prioritize to go through it a bit more properly, the more as it seems rich in images and not have too much text (exactly the way I like it )...

 

In any case, while I agree the way the striae reticulate in my specimen is not particularly pliosaurian, the reason I was initially sceptical of the tooth belonging to Machimosaurus sp., or even machimosauridae, is four-fold:

1. Most of the machimosaurid-teeth I've seen so far have clear anterior and posterior carinae. The carinae also often create distinct labial and lingual sides to such teeth. And even if both are convex, the lingual surface often seems a little offset labially from a true circle, giving the impression of somewhat of a compression (or two halves of a plastic cone, one side of which has been pressed a bit inward too much when connecting both sides).
2. Most machimosaurid-teeth I've seen so far have a clear area of anastomosing enamel at the tooth apex. And while the very tip has broken off of my specimen, there doesn't seem to be any indication of anastomosing enamel.
3. Machimosaurid-teeth I've seen are quite robust, as such not as recurved and with a much wider circular base. Young et al. (ibid.) describe this as "sub-globular".
4. My specimen has numerous striae, primarily on the buccal surface, that terminate at varying distances short of the apex. In machimosaurid-teeth I've seen, striae typically run the full apicobasal length of the tooth with minimum drop-out until they reach the area of anastomosing enamel.

Here are a couple of examples that illustrate this point:

 

 

 

 

 

 

 

 

 

 

 

Machimosaurus sp., Oxford Clay, Callovian. Two such specimens are known to me. With them both dating to the Callovian, Young et al. (ibid.) would assign them to 'Steneosaurus' obtusidens, but continue to describe similar teeth from the Oxfordian as varyingly 'S.' obtusidens and M. cf. hugii before landing on Machimosaurus sp.. Johnson et al. (2017, p. 4), however, describe these kind of teeth as Machimosaurus sp., an ascription I'll maintain (see also ibid., fig. 12E-I).

 

 

 

 

 

Machimosaurus sp. from the Kimmeridgian/Tithonian of the Lourinhã Formation, Portugal

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Interestingly, I do see some semblance with the below M. hugii, from the Lourinhã Formation in Portugal, with respect to the density of striations, termination of striae, bifurcation and reticulation. The M. hugii tooth also seems a bit less robust than the machimosaurid teeth figured above and doesn't exhibit clear carinae - which corresponds well to my specimen.

 

 

Young et al. (2014, p. 26) describe the teeth of machimosauridae as

Quote

conical [...] with blunt/rounded apices [...]; tooth enamel ornamentation varies along the crown, in the basal region enamel ornamentation is composed of numerous apicobasally aligned ridges of high relief, which become an anastomosed pattern in the apical region [...]; presence of carinae is variable, in anterior teeth they can be prominent but in shorter blunter teeth carinae are either very poorly developed or absent; [and] ratio of crown apicobasal height to basal transverse width can be as low as 1.5 in the posterior teeth[.]

 

With carinae not necessarily needing to be visible, machimosaurid teeth being densely packed with apicobasal striations, and the cross-section of my tooth being circular, I'd say it's very well possible that my tooth could indeed belong to machimosauridae. Based on it's similarity with M. hugii and considering the tooth may have a Late Kimmeridgian date, it may very well belong to Machimosaurus hugii. The density of striations on the lingual side is observably higher than on the labial side, however, concerning which Young et al. (2014, p. 21) remark that in

Quote

the French and German 'M.hugii' specimens no tooth crowns are sub-globidont [and] apicobasally aligned enamel ridges immediately adjacent to the apical anastomosed region are closely packed only on the lingual tooth surface, [whereas] on the labial surface these ridges are more widely spaced[.]

 

As such, it seems more reasonable to assign my specimen to M. buffetauti, to which they attribute the aforementioned French and German teeth. At time of writing, M. buffetauti was only known from the Early Kimmeridgian, however (see fig. 45, ibid.).

 

Teeth likely attributable to Machimosaurus buffetauti sp. nov.. Figure 21, ibid.

 

 

 

 

 

 

 

 

There are still some features that don't quite add up with my specimen, though (see photographs below, striae from labial side), such as

1. the tooth not appearing to have a rounded apex, as is the hallmark of machimosauridae (the tooth is near complete with only minor feeding damage to the tip that, when projected, appears pointed rather than round);
2. the absence of anastomosing enamel towards the tooth apex, with too little of the tip having broken off to explain away this absence; or
3. apicobasal ridges on the lingual side that stop short of reaching the apex.

 

 

The tooth could, of course, more generically belong to a teleosaurid, but for that I'm still trying to work out how variable striations can be (see my thread here)...

[DE&i]

I can see where your coming from as possible Faringdon sponge gravels matrix. I've a small piece of undescribed bone from Faringdon (poor photos). 

 

I've some other Faringdon fossils with that hint of gravely matrix your focusing on. 

[pachy-pleuro-whatnot-odon]

Thanks for sharing, Darren! Very informative and an intriguing fragment of bone...! Clearly pachyostic, as you would expect to find in a marine deposit, but hollow(ed out), and too thick-walled to be pterosaur... Any idea on what it could be from? Looks almost theropod, I'd say, if not for the fact that half of the space for cancellous bone seems to be filled in with dense/osteosclerotic bone.

 

In any case, the colour and composition of the matrix is very distinctive - much darker and browner than the matrix on/in my specimen, though with the same gravelly components. Not sure whether this actually proves or disproves my specimen coming from the Faringdon Sponge Gravels, and I'd probably need some more information on local stratigraphy to work that out. As it is, I'll trust in what @PointyKnight has shared on the stratigraphy of Wicklesham Pit.

 

As it is and until I learn more, I'll probably consider my tooth Machimosaurus buffetauti for it's bold and densely packed striations; absent/highly reduced carinae; similarity with the Portuguese M. hugii above; higher density of striae on the lingual than labial side; and the fact that the missing piece of the tooth apex seems sizeable enough for M. buffetauti's anastomosing enamel to still have been present when the tooth was hole.

 

Thanks for your help, everyone!

[PointyKnight]

On 5/6/2021 at 12:22 AM, pachy-pleuro-whatnot-odon said:

a quick glance-over of Young et al. (2014)

 

Sorry, I should have specified I was referring to the other YOUNG et al. 2014 Machimosaurus paper, this one with more close-up illustrations of the various tooth morphologies and enamel!

 

As for the morphological characters these are valid points, but it's important to note that they apply only some of the time: Carination, robustness, and enamel ornamentation are all highly dependant on position and ontogeny. The condition of these extremely blunt, robust teeth is something that only really arose in the posterior teeth of derived machimosaurines, especially Machimosaurini. Outside Machimosaurinae pointed and smooth apices appear to be a common condition, there's also a lot more info in the JOHNSON et al. 2020 Teleosauroid monograph.

 

On 5/6/2021 at 12:22 AM, pachy-pleuro-whatnot-odon said:

Interestingly, I do see some semblance with the below M. hugii, from the Lourinhã Formation in Portugal, with respect to the density of striations, termination of striae, bifurcation and reticulation. The M. hugii tooth also seems a bit less robust than the machimosaurid teeth figured above and doesn't exhibit clear carinae - which corresponds well to my specimen.

 

Great observation! This would fall under the example of what might represent more anterior dentition of smaller individuals. Ontogenetic changes in machimosaurs are still poorly understood since their fossil record is so spotty. A less robust juvenile dentition adapted to catch smaller prey would be entirely feasable!

[pachy-pleuro-whatnot-odon]

9 minutes ago, PointyKnight said:

Sorry, I should have specified I was referring to the other YOUNG et al. 2014 Machimosaurus paper, this one with more close-up illustrations of the various tooth morphologies and enamel!

 

Didn't spot there were two! But it looks like I should definitely add this article to my reading list as well. Especially those close-up photographs look very informative.

 

11 minutes ago, PointyKnight said:

As for the morphological characters these are valid points, but it's important to note that they apply only some of the time: Carination, robustness, and enamel ornamentation are all highly dependant on position and ontogeny. The condition of these extremely blunt, robust teeth is something that only really arose in the posterior teeth of derived machimosaurines, especially Machimosaurini. Outside Machimosaurinae pointed and smooth apices appear to be a common condition, there's also a lot more info in the JOHNSON et al. 2020 Teleosauroid monograph.

 

Although I'm aware that the posterior teeth of various crocodylomorph species are indeed more blunted than the anterior ones, I wasn't fully aware that the bluntness of the machimosaurine teeth I was familiar is something restricted solely to the back of the jaw - though now that I think of it, it does make sense. This probably means that the machimosaurid teeth I've seen so far mostly concerned teeth somewhat more towards the back of the jaw... I should really read up on marine crocodiles a bit more... Anyway, thanks again for this useful bit of information

 

16 minutes ago, PointyKnight said:

Great observation! This would fall under the example of what might represent more anterior dentition of smaller individuals. Ontogenetic changes in machimosaurs are still poorly understood since their fossil record is so spotty. A less robust juvenile dentition adapted to catch smaller prey would be entirely feasable!

 

To be fair, I hadn't even considered this. But, yeah, this again makes perfect sense, especially when considering the recent burst in publications describing ontogenetical variations in diet amongst various reptile clades. Thanks for all the help!

[Vulcanspotter]

I have found several teeth at the same location. Although they have been found in Faringdon Sponge gravel, they are actually derived from the Kimmeridge layer. The first image shows a Plesiosaur tooth in matrix and the second shows my small collection of  Croc teeth.

[pachy-pleuro-whatnot-odon]

2 hours ago, scouserdownsouth said:

I have found several teeth at the same location. Although they have been found in Faringdon Sponge gravel, they are actually derived from the Kimmeridge layer. The first image shows a Plesiosaur tooth in matrix and the second shows my small collection of  Croc teeth.

 

While the second batch of teeth is definitely metriorhynchid crocodile teeth, the first tooth is a teleosaur marine crocodile tooth, not a plesiosaur. You don't get that kind of striation on plesiosaur teeth.

[Vulcanspotter]

I found this about Teleosaurids.

 

Teleosaurids were a group of semi-aquatic crocodylomorphs with a fossil record that spanned the Jurassic Period. In the UK, abundant specimens are known from the Oxford Clay Formation (OCF, Callovian to lower Oxfordian), but are very rare in the Kimmeridge Clay.

 

As this tooth has been derived from the Kimmeridge layer,  if it is a Teleosaurid then it's a rare find. Looks like I will have to keep searching for a Plesiosaur tooth.