Looking for info on Temnodontosaurus eurycephalus

[pachy-pleuro-whatnot-odon]

Probably one of the most enigmatic species of Temnodontosaurus is Temnodontosaurus eurycephalus, owing to only one skull ever having been found. This particular species is often described as a snub-nosed temnodontosaur with massive teeth and heavy jaw muscles that it probably used to hunt other ichthyosaurs (and other marine reptiles). Its holotype is currently held by the Natural History Museum in London, with the below being some images of it, taken off of Wikipedia:

 

 

My interest with it, at present, lies with its dentition, with the morphology of its teeth. For I've seen some truly massive teeth and equally massive roots come out of Lyme Regis that I currently consider to belong to T. platyodon based on specimens labelled as such in the NHM collections (see images below for illustration, but please note that Ichthyosaurus platyodon is an old synonym for T. platyodon).

 

 

And while these teeth seem morphologically similar to the teeth of Mary, Tony Gill's T. platyodon specimen (image below; source), I find myself wondering how these teeth compare to those of T. eurycephalus. Unfortunately, however, I've been able to find very little information or quality photographs on this particular species. I'd therefore like to ask if anybody here has any photographs - in particular crisp/detailed ones of the dentition - or articles (regrettably, I can't access pay-walled) that they'd be willing to share.

 

 

Thanks in advance!

Edited July 3, 2021 by pachy-pleuro-whatnot-odon
Layout photographs and added some text

[pachy-pleuro-whatnot-odon]

@PointyKnight @The Amateur Paleontologist @Jaimin013 @Macrophyseter @paulgdls

[paulgdls]

All I can offer are some better photos of Mary's teeth. I believe Chris Moore may have another skull that could be Temnodontosaurus eurycephalus. 

 

 

[pachy-pleuro-whatnot-odon]

Thanks, Paul! Those are amazing photographs! And though not of T. eurycephalus, they do already help a lot.

 

For while something weird seems to be going on with the teeth on the bottom row of the third photograph - the ones that appear to have a prominent mesial carina, look compressed and have a posterior curvature, almost like the teeth of certain mosasaur species - these teeth do not look like a match for the ones identified as T. platyodon from the NHM. Rather, the teeth look more like the upscaled I. communis teeth of a Temnodontosaurus-species supposedly still undescribed (see images below), although Mary's teeth appear to have carinae, whereas this "undescribed" species doesn't - at least to my knowledge. Another interesting observation is that it looks like the plicidentine on these teeth, as with many other marine reptiles, becomes less prominent as the size of the animal increases, making the teeth look increasingly smooth as the animal ages. Still, I think, in that case, that T. platyodon indeed has teeth ornamented with enamel folds: Josef Anning's specimen had teeth like that, as now, as it turns out, does Mary.... This conclusion, however, seats on current identification of Mary as T. platyodon, rather than another species of Temnodontosaurus. So, would you, perchance, know how Mary was identified as indeed being T. platyodon?

 

 

Thanks for the tip about Chris too, by the way: if I don't get any other feedback on my post I might try getting in touch with him instead

[pachy-pleuro-whatnot-odon]

So, I came cross this video that featured some shots of Mary, the Temnodotosaur, on YouTube last week. And while the image quality is not all that great - certainly far from good enough to make out ornamentation - it does show the skull surrounded by some objects and signs that allow estimating the size of it's teeth. And from what I can make out, the teeth are definitely a lot bigger than those of the jaw section in my last post (directly above) - although I don't exclude this jaw could still belong to T. platyodon, just a younger specimen where the enamel folds are still a lot more obvious (I've now heard the argument be made for a number of different marine reptile clades that the older individuals got the less pronounced the ornamentation on their teeth may have been).

 

 

 

 

In any case, when I compare Mary's teeth with the rooted specimen below (approximately 6 cm), this specimen appears to match up favourably in terms of size. Furthermore, as can be seen in some of the photographs, this rooted specimen does have certain remnants of plicidentine folds on an otherwise seemingly unornamented polygonal tooth, in much the same was as Mary does. Also to be seen, however, are the incipient stages of an increasingly more polygonal shape to the tooth crown, including presence of a single carina.

 

 

 

 

This trend of increasingly more polygonal teeth with lesser and lesser ornamentation seems to continue as the teeth grown larger into sizes where a single tooth crown may measure 4 cm (and may be even larger). Yet even those huge teeth, in careful study, show traces of enamel folds, such that it seems likely that the specimens assigned to T. platyodon by the NHM in my original post are indeed just that. However, if this is indeed the case, there'd have been some truly huge individuals swimming around Lyme Regis so many millions of years ago, as the largest of these teeth I've seen measures well beyond the size of Mary's teeth. Moreover, this still doesn't resolve the fact that I haven't gotten any further with my quest to find out more on the dentition of T. eurycephalus.

 

 

Edited August 9, 2021 by pachy-pleuro-whatnot-odon

[pachy-pleuro-whatnot-odon]

On 7/6/2021 at 10:37 PM, pachy-pleuro-whatnot-odon said:

For while something weird seems to be going on with the teeth on the bottom row of the third photograph - the ones that appear to have a prominent mesial carina, look compressed and have a posterior curvature, almost like the teeth of certain mosasaur species - these teeth do not look like a match for the ones identified as T. platyodon from the NHM. Rather, the teeth look more like the upscaled I. communis teeth of a Temnodontosaurus-species supposedly still undescribed (see images below), although Mary's teeth appear to have carinae, whereas this "undescribed" species doesn't - at least to my knowledge. Another interesting observation is that it looks like the plicidentine on these teeth, as with many other marine reptiles, becomes less prominent as the size of the animal increases, making the teeth look increasingly smooth as the animal ages.

 

 

So I bumped into the below recently-sold jaw-segment, which description struck me for mentioning a key detail that may help me unravel the mystery of the undescribed Temnodontosaurus species mentioned above and why it may still belong to Temnodontosaurus platyodon, even though it's teeth look nothing like Mary's. I know it's vendor information, but have enough trust in the expertise of this particular one to accept the claim.

 

 

Quote

This particular jaw belonged to a juvenile as the snout is slightly curved upwards, a feature of sub adults.

That is, if we look at the images of the other specimen with similar teeth posted previously, there also seems to be a very slight curve in that jaw - much less noticeable however for the length of the section. As such, it's very well possible that this jaw-section too belonged to a sub-adult individual, probably of the same species if dentition is anything to go on. As such, the supposedly undescribed species of Temnodontosaurus may actually comprise sub-adult specimens of T. platyodon. This would fit my earlier observation that the plicidentine of T. platyodon teeth reduces with increase in the size of the teeth quite well. Meaning that Temnodontosaurus platyodon may have two separate but affiliated dental morphotypes based on the ontogenetic stage of an individual - sub-adults having teeth with clear plicidentine enamel folds, whereas adult specimens have more polygonal teeth with carinae and less well-defined folds - something not unheard of in other reptile clades, where juveniles often have different diets from adults.

 

On 8/9/2021 at 4:28 PM, pachy-pleuro-whatnot-odon said:

This trend of increasingly more polygonal teeth with lesser and lesser ornamentation seems to continue as the teeth grown larger into sizes where a single tooth crown may measure 4 cm (and may be even larger). Yet even those huge teeth, in careful study, show traces of enamel folds, such that it seems likely that the specimens assigned to T. platyodon by the NHM in my original post are indeed just that.

[pachy-pleuro-whatnot-odon]

I think I may finally have made a break-through with this question! About two weeks ago I received the book "Ichthyosaurs from the Early Jurassic of Britain" by Weedon and Chapman (2022), containing a lot of figurative material on various ichthyosaur genera and species - including Temnodontosaurus eurycephalus! And since not much is known of this species except for a single skull (at present), a lot of focus on the description of the species has done into describing the dentition. The below images are taken from Fig. 13.8 (p. 183):

 

 

As you can see, while the roots still have the hallmark folds of the teeth of other ichthyosaur genera, the crowns lack the plicidentine enamel folds associated with most other ichthyosaur species. Instead, the teeth appear polygonal in much the same way as those specimens that originally prompted my question one-and-a-half year ago. Moreover, the description of the teeth includes the following statements (p. 183-184):

 

Quote

The teeth are robust and large (maximum total length 54 mm, McGowan, 1996a). [...] Many of the teeth show a narrowing from the root to the crown ('inflated roots', Fig. 13.8b). Also, unlike the teeth of T. platyodon, where they narrow the strong ridges of the roots stop so there is a smooth zone below the striae of the crown.  [...] Very large isolated teeth from Lyme Regis, up to 116 mm total length, were recorded by McGowan (1996a; i.e. NHMUK PV OR 28283, 28284 and 28310). [...] Assuming the large isolated teeth belong to the same species then the holotype of T. eurycephalus represents a juvenile or young adult.

 

These inventory numbers correspond with those on the Natural History Museum's specimens I shared in my original post, confirming that these actually shouldn't be attributed to T. platyodon, but to T. eurycephalus instead. Further confirmation is found in the list of synonyms Weedon and Chapman (2022) provide for T. eurycephalus, which includes the Ichthyosaurus platyodon mentioned on their labels.

 

Thus, while it does seem true that certain species of ichthyosaur changed their dentition as they matured - e.g., Dick and Maxwell's [2015] example of tooth reduction in Stenopterygius or the reduction how pronounced plicidentine enamel folds are in adult specimens of T. platyodon - the teeth I started this thread about (and that occasionally are confused for those of pliosaurs) can now firmly be attributed to T. eurycephalus.