Plesiosaur or Ichthyosaur tooth? Goulmima, Morocco

[msantix]

Hi,

 

I always struggle to tell the difference between a Plesiosaur tooth and an Ichthyosaur tooth. This tooth comes from Goulmima in Morocco (lower Turonian) so I believe it is a Plesiosaur tooth (possibly a Pliosaur tooth), but wanted to confirm it here. The tooth is 4.2cm in length and retains the ridges on the tooth which I think is how you might tell the difference between Plesiosaur and Ichthyosaur. Thank you!

 

[DatFossilBoy]

That’s a Pliosaurus tooth

[msantix]

Cool, so the tooth could be from Brachauchenius Lucasi since a paper described that species from the Goulmima site in Morocco

[Troodon]

The holotype had 3 unerupted teeth this was the best one

With this description " It has a rounded cross-section and the enamel is ornamented with heavily striae all around and some branching striae toward the base of the crown. The teeth are large, posteriorly recurved rounded cones. "

 

"

A new record of the pliosaur Brachauchenius lucasi Williston, 1903 (Reptilia: Sauropterygia) of Turonian (Late Cretaceous) age, Morocco
Published online by Cambridge University Press:  05 August 2015

 

 

[msantix]

Thanks, I have seen the holotype. I think it looks similar with the rounded cross-section & the slight curve.

[pachy-pleuro-whatnot-odon]

Wow! How do you do it? You're the only person I know who consistently manages to pick these kind of teeth up! Conservation leaves a bit to be desired, but still: what a beaut!!

 

This is definitely pliosaur, though, based on the following:

1. Ichthyosaurs are currently assumed to have gone extinct at the Cenomanian-Turonian boundary, making the find of an ichthyosaur tooth less likely.
2. While platypterygiine ichthyosaurs - i.e., the main group of derived parvipelvians that survived into the Cretaceous - have a rounded neck to their root (see the discussion here, here and here), this would be more consistently round and not as bulbous or smooth as in this specimen. Instead, the features of the root on this specimen are typical of plesiosaurian teeth.
3. First and foremost, though, is tooth ornamentation: ichthyosaurs have plicidentine enamel folds, which look rounded, whereas pliosaurs have much sharper striations - triangular to square in cross-section (see image below). The enamel-folds of ichthyosaurs are also much more regularly distributed around the circumference of the tooth, whereas the density of may differ from place to place (see this discussion for some examples of pliosaurian teeth from other locations). Other telling features indicative of pliosaurian teeth are striae splitting/bifurcating and merging/reticulating (though not always present); striae not starting at the base (again, not always present); vermiculated tooth enamel (also not always present); and carina-like apical fusion of striae (once more, not always present). These features are in contrast with those of ichthyosaurian teeth, as the folds never bifurcate or reticulate, always start at the base, enamel is consistently smooth, and all except for a few species don't have carina (see here). A final distinguishing feature of tooth ornamentation is that in derived, ophthalmosaurid ichthyosaurs the enamel folds stop short of reaching the apicobasal height of the tooth crown, with all folds stopping at the same height. In pliosaurs, striae don't top at the same height.
   
   Cross-sections through the teeth of A. Polyptycodon interruptus, B. Globidens alabamensis, C. Goniopholis crassidens, D. Spinosaurus aegyptiacus, E. Ichthyosaurus communis, F. Zygorhiza kochii. Figure 4 from McCurry et al., 2019. The repeated evolution of dental apicobasal ridges in aquatic-feeding mammals and reptiles

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Finally, for completeness, here are some plesiosaur teeth of differing morphologies from the Goulmima/Asfla region (some of which are from msantix's own posts!):

 

Elasmosaur tooth (based on fine meandering striations), cf. Libonectes atlasense

 

 

 

 

 

 

 

 

 

 

 

 

Polycotylidae indet., i.e. either Thililua longicollis or Manemergus anguirostris (see also this post)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As a bonus - just to see some more examples of Moroccan plesiosaur teeth that are not Z. oceanis - here's another plesiosaur tooth from the Cenomanian (Cretaceous) of Boujdour in the Western Sahara. Species may be Libonectes atlasense:

 

[Jared C]

On 4/28/2021 at 11:00 AM, pachy-pleuro-whatnot-odon said:

Wow! How do you do it? You're the only person I know who consistently manages to pick these kind of teeth up! Conservation leaves a bit to be desired, but still: what a beaut!!

 

This is definitely pliosaur, though, based on the following:

1. Ichthyosaurs are currently assumed to have gone extinct at the Cenomanian-Turonian boundary, making the find of an ichthyosaur tooth less likely.
2. While platypterygiine ichthyosaurs - i.e., the main group of derived parvipelvians that survived into the Cretaceous - have a rounded neck to their root (see the discussion here, here and here), this would be more consistently round and not as bulbous or smooth as in this specimen. Instead, the features of the root on this specimen are typical of plesiosaurian teeth.
3. First and foremost, though, is tooth ornamentation: ichthyosaurs have plicidentine enamel folds, which look rounded, whereas pliosaurs have much sharper striations - triangular to square in cross-section (see image below). The enamel-folds of ichthyosaurs are also much more regularly distributed around the circumference of the tooth, whereas the density of may differ from place to place (see this discussion for some examples of pliosaurian teeth from other locations). Other telling features indicative of pliosaurian teeth are striae splitting/bifurcating and merging/reticulating (though not always present); striae not starting at the base (again, not always present); vermiculated tooth enamel (also not always present); and carina-like apical fusion of striae (once more, not always present). These features are in contrast with those of ichthyosaurian teeth, as the folds never bifurcate or reticulate, always start at the base, enamel is consistently smooth, and all except for a few species don't have carina (see here). A final distinguishing feature of tooth ornamentation is that in derived, ophthalmosaurid ichthyosaurs the enamel folds stop short of reaching the apicobasal height of the tooth crown, with all folds stopping at the same height. In pliosaurs, striae don't top at the same height.
   
   Cross-sections through the teeth of A. Polyptycodon interruptus, B. Globidens alabamensis, C. Goniopholis crassidens, D. Spinosaurus aegyptiacus, E. Ichthyosaurus communis, F. Zygorhiza kochii. Figure 4 from McCurry et al., 2019. The repeated evolution of dental apicobasal ridges in aquatic-feeding mammals and reptiles

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Finally, for completeness, here are some plesiosaur teeth of differing morphologies from the Goulmima/Asfla region (some of which are from msantix's own posts!):

 

Elasmosaur tooth (based on fine meandering striations), cf. Libonectes atlasense

 

 

 

 

 

 

 

 

 

 

 

 

Polycotylidae indet., i.e. either Thililua longicollis or Manemergus anguirostris (see also this post)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As a bonus - just to see some more examples of Moroccan plesiosaur teeth that are not Z. oceanis - here's another plesiosaur tooth from the Cenomanian (Cretaceous) of Boujdour in the Western Sahara. Species may be Libonectes atlasense:

 

Every time I read a post from you it it just world class. What a fantastic explanation