Ichthyosaur or pliosaur tooth?

[Per Christian]

Hello all

 

I acquired this tooth recently. It's those famous russian deposits that produce ichthyosaur and pliosaur remains. I bought it as an ichthyosaur tooth, but could it be it's pliosaur? I've noticed rootef ichthyosaur teeth have a bit different root, like a pronged root.  But I'm hardly an expert so I'd greatly appreciate feedback from others

 

 

 

 

 

 

 

[DatFossilBoy]

Ichthyosaurus, and a super nice one! 
Great tooth 

[Guns]

+1 Ichthy tooth  . Good quality congrat mate !

[pachy-pleuro-whatnot-odon]

As has been said, this is a platypterygine ichthyosaur tooth. Ichthyosaur teeth, due to their plicidentine-condition, have much rounder and more consistent enamel folds on their tooth crowns than are the pliosaurian striations, which are much more crisp, with a triangular to square cross-section, but often occur at much less consistent intervals than is the case here. Compare the images below:

 

Ophthalmosaurine ichthyosaur teeth from the Cambridge Greensand. Figure 11 from Fischer, Bardet, Guiomar and Godefroit, 2014. High Diversity in Cretaceous Ichthyosaurs from Europe Prior to Their Extinction

 

 

 

 

 

 

 

 

 

 

 

A 5cm(!) pliosaur tooth from Fedorovka in Russia. Source: Ammonit.ru

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Another point to note is that in ophthalmosaurine ichthyosaurs, the enamel-folds do not reach the tooth apex, much as is as is the case here, were the enamel cap still in place. For comparison, here's a Platypterygius cf. campylodon tooth from Dörenthe, Ibbenbüren, in Germany:

 

 

And while it is true that the root on OP's specimen seems rather long for an ichthyosaur tooth, the top of the root (nearest the crown) is bulbous and striated as observed by Fischer et al. (2014). Moreover, the lower part of the root seems more of a rounded rectangular shape than fully circular, which again matches the shape of the roots of more derived ichthyosaurs (with less derived species having folded and rounded roots).

[Per Christian]

50 minutes ago, pachy-pleuro-whatnot-odon said:

As has been said, this is a platypterygine ichthyosaur tooth. Ichthyosaur teeth, due to their plicidentine-condition, have much rounder and more consistent enamel folds on their tooth crowns than are the pliosaurian striations, which are much more crisp, with a triangular to square cross-section, but often occur at much less consistent intervals than is the case here. Compare the images below:

 

Ophthalmosaurine ichthyosaur teeth from the Cambridge Greensand. Figure 11 from Fischer, Bardet, Guiomar and Godefroit, 2014. High Diversity in Cretaceous Ichthyosaurs from Europe Prior to Their Extinction

 

 

 

 

 

 

 

 

 

 

 

A 5cm(!) pliosaur tooth from Fedorovka in Russia. Source: Ammonit.ru

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Another point to note is that in ophthalmosaurine ichthyosaurs, the enamel-folds do not reach the tooth apex, much as is as is the case here, were the enamel cap still in place. For comparison, here's a Platypterygius cf. campylodon tooth from Dörenthe, Ibbenbüren, in Germany:

 

 

And while it is true that the root on OP's specimen seems rather long for an ichthyosaur tooth, the top of the root (nearest the crown) is bulbous and striated as observed by Fischer et al. (2014). Moreover, the lower part of the root seems more of a rounded rectangular shape than fully circular, which again matches the shape of the roots of more derived ichthyosaurs (with less derived species having folded and rounded roots).

Wow what a consice response you wrote. Thank you! I really appreciate it. I have no way of acquiring that kind of knowledge so I'm in awe of the help i get here

[pachy-pleuro-whatnot-odon]

6 minutes ago, Per Christian said:

Wow what a consice response you wrote. Thank you! I really appreciate it. I have no way of acquiring that kind of knowledge so I'm in awe of the help i get here

You're very welcome! It's been a bit of a road for me too. A lot of collecting, reading, comparing, browsing the internet and validating formed opinions. I can highly recommend it

[Per Christian]

9 minutes ago, pachy-pleuro-whatnot-odon said:

You're very welcome! It's been a bit of a road for me too. A lot of collecting, reading, comparing, browsing the internet and validating formed opinions. I can highly recommend it

I'm working on it with good help from you guys!

[Mike from North Queensland]

Another point is that pliosaur teeth tend to be round at the root as they grow from a socket in the jaw.

The ichthyosaur teeth tend to be more rectangular at the root as they grow from a jaw groove.

A end photo would also have helped.

[pachy-pleuro-whatnot-odon]

2 hours ago, Mike from North Queensland said:

Another point is that pliosaur teeth tend to be round at the root as they grow from a socket in the jaw.

The ichthyosaur teeth tend to be more rectangular at the root as they grow from a jaw groove.

Though this is generally true, I understand this does vary with the position in the jaw, with roots becoming more cylindrical towards the distal end of the rostrum. In fact, the root of ichthyosaur teeth may be anywhere from round through subtriangular to rectangular - which I suspect might be the result of differing compressional forces at work what I believe could be mineralised periodontal ligaments that form ichthyosaur tooth roots (for an interesting discussion on tooth attachment and its related tissues in mosasaurs, see here).

 

In any case, ichthyosaur tooth roots are not typically as smooth as the tubercular, or pen-like, plesiosaurian ones, instead having folds, striae or other roughenings.

[-Andy-]

As someone who owns both type of teeth, this gets another vote of Ichthyosaur from me

[Per Christian]

Here are some bottom-photos. Don't know if they help clear it up further?

[pachy-pleuro-whatnot-odon]

2 hours ago, Per Christian said:

Here are some bottom-photos. Don't know if they help clear it up further?

 

11 hours ago, Mike from North Queensland said:

Another point is that pliosaur teeth tend to be round at the root as they grow from a socket in the jaw.

The ichthyosaur teeth tend to be more rectangular at the root as they grow from a jaw groove.

The root is square in cross-section, so, again, confirmation of this tooth being an ichthyosaurian one.

[Mike from North Queensland]

The first photo shows the typical shape of the root of an ichthyosaur.

The hole in the bottom of the tooth is caused from a replacement tooth starting to erupt.