Mongolian carnivore tooth with jaw fragment. Is this a croc or theorpod?

[-Andy-]

 

Hi all, I had posted about this tooth years ago and the conclusion back then was that its preservation was too poor for any proper ID. I am hoping that with new information we can at least determine if this is a crocodile or theropod. I discovered today that this tooth preserved some serrations

 

First up, this tooth was acquired from a source with many Mongolian material. He called this an Alioramus tooth but I am not comfortable calling it that yet

 

Secondly, a museum curator (who has handled Mongolian material) examined this tooth in person. He concluded this tooth was indeed Mongolian but he could only say it's a carnivore. Unfortunately, we are unable to determine which part of Mongolia it came from.

 

The crown is 40 mm in a straight line. I have quite a number of croc and theropod teeth and this tooth feels much closer to a theropod than a crocodile both in terms of morphology and size. However, I am not unbiased in my ID, and the shallow jaw fragment is throwing me off. Assuming this is indeed from a tyrannosaur, I'd expect the jaw to be much deeper. Please let me know your honest thoughts, thank you

 

 

 

Comparison of tooth to a cf. Daspletosaurus from the Judith River Formation

[-Andy-]

Here are a group of Alioramus jaw

 

 

Here's a Tarbosaurus jaw from Mongolia

 

 

[Troodon]

Not again   

[-Andy-]

15 minutes ago, Troodon said:

Not again   

 

Unfortunately I didn't give you the right info the first time so that's on me. My locality data was off, and I mistakenly assumed no serrations were preserved

 

Even if your answer isn't one I'd like, it's still important for me to know your thoughts on this fossil because I value your opinion

[Troodon]

I understand but not sure we will get there.  I dont think its crocodilian looks to compressed.   Without a locality we don't when know if its Cretaceous could be cenozoic but I agree what I'm seeing it looks like Mongolian.

Are those serrations were are seeing or just a  jaggard edge?  Also the shape is not helped by missing all the enamel on one side just denying present.   Can you determine what the cross-section looks at the base tip and midline.  Midline looks triangular.  

[-Andy-]

28 minutes ago, Troodon said:

I understand but not sure we will get there.  I dont think its crocodilian looks to compressed.   Without a locality we don't when know if its Cretaceous could be cenozoic but I agree what I'm seeing it looks like Mongolian.

Are those serrations were are seeing or just a  jaggard edge?  Also the shape is not helped by missing all the enamel on one side just denying present.   Can you determine what the cross-section looks at the base tip and midline.  Midline looks triangular.  

 

I can't deny the mesial serrations may be a jagged edge, but the distal serrations in this red square I am 100% positive are proper serrations. Also, the original enamel is still preserved here

 

As for cross section, this is what it looks like. For the mid line, the missing gaps are where chunks of enamel are missing from. As before, it feels almost like there is a 3rd carina between the distal and mesial edges and I can't understand why. I am unsure if it's due to the tooth's natural morphology, or due to deformation and missing enamel that shaped it so

 

[pachy-pleuro-whatnot-odon]

1 hour ago, Troodon said:

I understand but not sure we will get there.  I dont think its crocodilian looks to compressed.   Without a locality we don't when know if its Cretaceous could be cenozoic but I agree what I'm seeing it looks like Mongolian.

Are those serrations were are seeing or just a  jaggard edge?  Also the shape is not helped by missing all the enamel on one side just denying present.   Can you determine what the cross-section looks at the base tip and midline.  Midline looks triangular.  

I agree, to me the tooth looks too compressed to be crocodile too.

 

22 minutes ago, -Andy- said:

I can't deny the mesial serrations may be a jagged edge, but the distal serrations in this red square I am 100% positive are proper serrations. Also, the original enamel is still preserved here

Like @Troodon, I'm also doubtful that these are proper serrations. That is, though I do concede, on the left, there are three bumps in a row that look like part of a serration, 1) the rest of the carina is too damaged to see whether the serration continues; 2) it's possible, even if unlikely, these bumps came about naturally, either due to feeding or because of post-depositional processes; and 3) to my limited knowledge a lot of serrations are not just a series of bumps, but have a base on the tooth itself - i.e. grooves outlining individual elements of the serrations. To illustrate that last point, here are some images I plucked off the internet:

 

 

 

 

 

 

 

 

 

 

 

 

And as an unrelated illustration of how this concept seems to carry across clades and therefore might be part of the very concept of serrations:

 

 

What doesn't help is that the tooth looks deformed, with the one side of the tip (what looks to be the lingual side) having been pressed into the other. With this type of deformation present, I think it'd be hard to say whether what I'm seeing in the photographs below is a third carina, deformation, or just the angle the photograph was taken in:

 

2 hours ago, -Andy- said:

 

Comparison of tooth to a cf. Daspletosaurus from the Judith River Formation

 

And then there's the fact that it looks like only the labial side of the tooth appears to have left-overs of the original enamel, while the rest of the tooth seems to be comprised of mostly dentine. As such, it's hard to say whether the supposed serrations on the edge of the tooth are not just the places where the enamel tore/break/weathered off.

 

Probably not much of a help, but may be it gets the discussion going.

[Troodon]

I trust your call on the distal serrations.  Cross-section are what I would expect.  I cannot definitely say its Theropod without a locality and state of preservation but I a good chance its one.  Beyond that would be a pure guess.

[-Andy-]

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

I agree, to me the tooth looks too compressed to be crocodile too.

 

Like @Troodon, I'm also doubtful that these are proper serrations. That is, though I do concede, on the left, there are three bumps in a row that look like part of a serration, 1) the rest of the carina is too damaged to see whether the serration continues; 2) it's possible, even if unlikely, these bumps came about naturally, either due to feeding or because of post-depositional processes; and 3) to my limited knowledge a lot of serrations are not just a series of bumps, but have a base on the tooth itself - i.e. grooves outlining individual elements of the serrations. To illustrate that last point, here are some images I plucked off the internet:

 

And as an unrelated illustration of how this concept seems to carry across clades and therefore might be part of the very concept of serrations:

 

What doesn't help is that the tooth looks deformed, with the one side of the tip (what looks to be the lingual side) having been pressed into the other. With this type of deformation present, I think it'd be hard to say whether what I'm seeing in the photographs below is a third carina, deformation, or just the angle the photograph was taken in:

 

And then there's the fact that it looks like only the labial side of the tooth appears to have left-overs of the original enamel, while the rest of the tooth seems to be comprised of mostly dentine. As such, it's hard to say whether the supposed serrations on the edge of the tooth are not just the places where the enamel tore/break/weathered off.

 

Probably not much of a help, but may be it gets the discussion going.

 

Thank you for your analysis and help. For the mesial serrations, I agree that it's questionable if those are proper denticles or parts For the distal serrations, I am so certain because the parts of the tooth in the red square are not torn or broken, but are of the original enamel. It's something that doesn't translate well through photos.

 

Most of the other parts of the tooth are just a tooth core, so yeah it's a problematic tooth for sure.

 

11 hours ago, Troodon said:

I trust your call on the distal serrations.  Cross-section are what I would expect.  I cannot definitely say its Theropod without a locality and state of preservation but I a good chance its one.  Beyond that would be a pure guess.

 

I understand. I have learnt much since then to always insist on detailed locality data. This tooth will serve as an important lesson

 

A tyrannosaurid paleontologist replied this: Without more data it’s impossible to identify except it appears to be a theropod tooth.

[Pemphix]

13 hours ago, Troodon said:

I trust your call on the distal serrations.  Cross-section are what I would expect.  I cannot definitely say its Theropod without a locality and state of preservation but I a good chance its one.  Beyond that would be a pure guess.

[Runner64]

On 12/3/2020 at 9:40 AM, -Andy- said:

However, I am not unbiased in my ID, and the shallow jaw fragment is throwing me off.

@-Andy- I am not sure how I missed this topic.  I have certainly seen this piece before but haven't taken a hard look at it.  Anyways, are you sure the piece in question is a tooth?  If so, that would be a very large tooth for a very shallow root.  That would almost certainly rule out any large-bodied carnivore that would need a rigid root to anchor their teeth in place.  The part you brought up here is what I initially thought when I saw these photos.  Also, the tooth doesn't seem to have a root in the jaw and is not independent from the matrix in one photo.  Maybe in the angle, but are you confident enough to rule out a worn piece of bone or suggested rock?

 

I agree the matrix looks Mongolian and matches several formations in the southern and western part of the country.

 

Doesn't really help with an ID I suppose but just some observations I made.

[-Andy-]

7 hours ago, Runner64 said:

@-Andy- I am not sure how I missed this topic.  I have certainly seen this piece before but haven't taken a hard look at it.  Anyways, are you sure the piece in question is a tooth?  If so, that would be a very large tooth for a very shallow root.  That would almost certainly rule out any large-bodied carnivore that would need a rigid root to anchor their teeth in place.  The part you brought up here is what I initially thought when I saw these photos.  Also, the tooth doesn't seem to have a root in the jaw and is not independent from the matrix in one photo.  Maybe in the angle, but are you confident enough to rule out a worn piece of bone or suggested rock?

 

I agree the matrix looks Mongolian and matches several formations in the southern and western part of the country.

 

Doesn't really help with an ID I suppose but just some observations I made.

 

I am sure this is a tooth

 

Back then, I did ask the museum curator who handled this fossil about this. He said there's a chance the tooth could have been stuck onto an empty jaw socket

 

I examined the jaw fragment again. This is the bottom of it. It's broken and deformed. The areas I highlighted in red are broken off. I do not know what's under the red matrix but if the broken section of bone continues there, then there's a chance the jaw isn't that shallow after all