Aust Plesiosaur fossil ID

[Alston Gee]

Can someone help me identify the tooth fossil found at Aust Cliff, Bristol, UK? According to the seller, this fossil is presumed to be a Triassic plesiosaur tooth, likely classified as a basal plesiosaur. Nevertheless, the striation pattern on the lingual side of the tooth raises doubts about whether it could also be an ichthyosaur tooth.

 

[Alston Gee]

@pachy-pleuro-whatnot-odon 

Edited November 19, 2023 by Alston Gee

[pachy-pleuro-whatnot-odon]

Unfortunately the photographs seem to be inaccessible/missing. Could you post them again?

[Alston Gee]

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

Unfortunately the photographs seem to be inaccessible/missing. Could you post them again?

It seems the system automatically removed these pictures after the maintenance. 
 

[pachy-pleuro-whatnot-odon]

Nah, that's plesiosaur and not ichthyosaur. I've got it bookmarked as well. You can tell by the root if not by the nature of the striations themselves. Ichthyosaur tooth roots are folded, whereas those of plesiosaurs and crocodiles are smooth. Have a look at the below specimen of Ichthyosaurus communis from Hock Cliff in the UK to see what I mean...

 

 

As to species identification, the tooth can probably tentatively be ascribed to Eurycleidus arcuatus, which seems to be the only species described from the location. Compare with the specimen below:

 

 

Also, please note that this seems to be just a splinter of a tooth, that does not necessarily continue further into the matrix.

[Alston Gee]

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

Nah, that's plesiosaur and not ichthyosaur. I've got it bookmarked as well. You can tell by the root if not by the nature of the striations themselves. Ichthyosaur tooth roots are folded, whereas those of plesiosaurs and crocodiles are smooth. Have a look at the below specimen of Ichthyosaurus communis from Hock Cliff in the UK to see what I mean...

 

 

As to species identification, the tooth can probably tentatively be ascribed to Eurycleidus arcuatus, which seems to be the only species described from the location. Compare with the specimen below:

 

 

Also, please note that this seems to be just a splinter of a tooth, that does not necessarily continue further into the matrix.

I'm not quite sure how many plesiosaur species are found at Aust Cliff, but the Westbury Formation is documented to have Atychodracon sp. and Eurycleidus sp. Would this alter the identity of this tooth fossil? I notice that Eurycleidus sp. teeth usually have ornamentation on its lingual and buccal sides only, but some plesiosaur teeth from Westbury formation were observed to have striae covering the entire tooth crown. 

[Alston Gee]

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

Nah, that's plesiosaur and not ichthyosaur. I've got it bookmarked as well. You can tell by the root if not by the nature of the striations themselves. Ichthyosaur tooth roots are folded, whereas those of plesiosaurs and crocodiles are smooth. Have a look at the below specimen of Ichthyosaurus communis from Hock Cliff in the UK to see what I mean...

 

 

As to species identification, the tooth can probably tentatively be ascribed to Eurycleidus arcuatus, which seems to be the only species described from the location. Compare with the specimen below:

 

 

Also, please note that this seems to be just a splinter of a tooth, that does not necessarily continue further into the matrix.

I recently acquired a Triassic plesiosaur tooth from Westbury Formation. This tooth has a similar striation pattern and morphology as Atychodracon megacephalus tooth (Cruickshank, 1994). What’s your thoughts?

[pachy-pleuro-whatnot-odon]

18 hours ago, Alston Gee said:

I'm not quite sure how many plesiosaur species are found at Aust Cliff, but the Westbury Formation is documented to have Atychodracon sp. and Eurycleidus sp. Would this alter the identity of this tooth fossil? I notice that Eurycleidus sp. teeth usually have ornamentation on its lingual and buccal sides only, but some plesiosaur teeth from Westbury formation were observed to have striae covering the entire tooth crown. 

 

Aust Cliff exposes both the Westbury Formation as part of the Rhaetian Penarth Group as well as the Hettingian Blue Lias Formation (see below image; source). The list of species should therefore include all species from the Westbury Formation as well as those that persisted into the Blue Lias. As the latter includes Eurycleidus arcuatus, I expect there to be a slight over-representation of that species at the locality (see here for teeth I've identified as Eurycleidus arcuatus from Lyme Regis); though if we strictly consider the Westbury Formation, which contains the bone-bed, both Atychodracon megacephalus and Eurycleidus arcuatus should be possible.

 

 

The problem here is that there's quite a bit of taxonomic overlap between A. megacephalus and E. arcuatus, with cladistics variously recovering the former as either a sister or ancestral taxon to the latter. One would therefore not be surprised to find a great deal of similarity in their dentition as well, which indeed seems to be the case when you describe E. arcuatus as having striae on both lingual and buccal sides of the tooth (i.e., around the entire circumference), and the teeth of A. megacephalus also being entirely covered in striations. To me, therefore, there doesn't seem to be a way to differentiate between the two genera/species.

 

Storrs (p. 228) in Swift and Martill's (eds.) 1999 volume "Fossils of the Rhaetian Penarth Group" (also referred to here) seemingly echoes these sentiments when he 1) describes plesiosaur teeth from Aust Cliff as rather uniformly "large, sharp, curved and striated"; and 2) as Eurycleidus arcuatus being the primary identifiable species at Aust Cliff. Strictly speaking, however, I suspect a clear distinction between Atychodracon megacephalus and Eurycleidus arcuatus cannot be made.

[Alston Gee]

On 11/24/2023 at 3:01 AM, pachy-pleuro-whatnot-odon said:

 

Aust Cliff exposes both the Westbury Formation as part of the Rhaetian Penarth Group as well as the Hettingian Blue Lias Formation (see below image; source). The list of species should therefore include all species from the Westbury Formation as well as those that persisted into the Blue Lias. As the latter includes Eurycleidus arcuatus, I expect there to be a slight over-representation of that species at the locality (see here for teeth I've identified as Eurycleidus arcuatus from Lyme Regis); though if we strictly consider the Westbury Formation, which contains the bone-bed, both Atychodracon megacephalus and Eurycleidus arcuatus should be possible.

 

 

The problem here is that there's quite a bit of taxonomic overlap between A. megacephalus and E. arcuatus, with cladistics variously recovering the former as either a sister or ancestral taxon to the latter. One would therefore not be surprised to find a great deal of similarity in their dentition as well, which indeed seems to be the case when you describe E. arcuatus as having striae on both lingual and buccal sides of the tooth (i.e., around the entire circumference), and the teeth of A. megacephalus also being entirely covered in striations. To me, therefore, there doesn't seem to be a way to differentiate between the two genera/species.

 

Storrs (p. 228) in Swift and Martill's (eds.) 1999 volume "Fossils of the Rhaetian Penarth Group" (also referred to here) seemingly echoes these sentiments when he 1) describes plesiosaur teeth from Aust Cliff as rather uniformly "large, sharp, curved and striated"; and 2) as Eurycleidus arcuatus being the primary identifiable species at Aust Cliff. Strictly speaking, however, I suspect a clear distinction between Atychodracon megacephalus and Eurycleidus arcuatus cannot be made.

Hi Alexander,

 

Sorry for this late reply. I noticed that you haven’t responded to my last question regarding the identification of the tooth from Westbury Formation. Which label would you give to that tooth? Is it indeed a basal plesiosaur tooth or something else? 

[pachy-pleuro-whatnot-odon]

9 minutes ago, Alston Gee said:

Hi Alexander,

 

Sorry for this late reply. I noticed that you haven’t responded to my last question regarding the identification of the tooth from Westbury Formation. Which label would you give to that tooth? Is it indeed a basal plesiosaur tooth or something else? 

 

Sorry about that! I guess I must've overlooked the question there... But, yes, it's indeed a plesiosaurian tooth, of the type usually identified as Eurycleidus arcuatus, which is indeed a rhomaleosaur.