Tiny Hell Creek Tyrannosaur tooth?

[jikohr]

Hi everyone,

 

About a week ago I posted pictures of a tiny carnivorous dinosaur tooth from Hell Creek thinking it was raptor and it wound up being Tyrannosaur. Since then I've been taking a closer look at my other tiny teeth and this one which I thought was Acheroraptor stuck out to me when I took a closer look at the serrations. It also occurred to me that there are serrations (although very worn that I for the life of me could not get a decent shot of but are present) on the anterior carina which you don't see on Acheroraptor teeth so now I'm leaning more towards a tiny Tyrannosaur, but I'm still learning so I was hoping for a second opinion.

 

Thanks as always!

[Troodon]

Need the following.

CH, CBL & CBW

Density both carinae midline okay with 2 or 3mm wide

 

[ThePhysicist]

I think your original thinking was correct. The longitudinal ridges on the crown faces and the apparent dissimilarity of the serrations on each carina are diagnostic characteristics of Acheroraptor. Would be nice to have measurements to confirm that as Frank requested.

47 minutes ago, jikohr said:

there are serrations (although very worn that I for the life of me could not get a decent shot of but are present) on the anterior carina which you don't see on Acheroraptor teeth so now I'm leaning more towards a tiny Tyrannosaur, but I'm still learning so I was hoping for a second opinion.

Acheroraptor and other Dromaeosaurs can certainly have mesial serrations - the feature you're looking for is the difference in serration densities. Compare with this magnificent specimen of @JoeS's:

[jikohr]

32 minutes ago, Troodon said:

Need the following.

CH, CBL & CBW

Density both carinae midline okay with 2 or 3mm wide

 

CH=~7 mm

CBL=~3.5 mm

CBW=~1.5 mm

mesial serration count: 29 per 3mm

distal serration count 20 per 3mm

[jikohr]

10 minutes ago, ThePhysicist said:

I think your original thinking was correct. The longitudinal ridges on the crown faces and the apparent dissimilarity of the serrations on each carina are diagnostic characteristics of Acheroraptor. Would be nice to have measurements to confirm that as Frank requested.

Acheroraptor and other Dromaeosaurs can certainly have mesial serrations - the feature you're looking for is the difference in serration densities. Compare with this magnificent specimen of @JoeS's:

By any chance do you have a similar picture for Dakotaraptor?

I know this tooth isn't Dakotaraptor but just to have for a reference like this would be very helpful!

[Troodon]

Thanks.   This is an interesting tooth since it has very little recurve, chisel denticles which are not typical of the holotype teeth of Acheroraptor nor JoeS's tooth but more similar to Dakotaraptor teeth which are more upright but have rounded denticles.   Both are Dromaeosaurids why I asked for more information.   Unfortunately we have very little knowledge of what these dentition look like since both holotypes have very few teeth described why looking and comparing morphometric measurements to what is known.   A serration density ratio (DSDI) above 1.4 would be typical of the holotype teeth and seems too high for Nanotyrannus, yours is 1.45.   The Crown Height ratio ratios lean more Nanotyrannus.   Isolated teeth can be difficult to diagnose but it's probably an Acheroraptor but I cannot definitively say that given the shape of the denticles.   I would identify it as indeterminate. 

[Troodon]

You mentioned Dakotaraptor teeth.   These can be very difficult to diagnose since they look very similar to Nanotyrannus teeth.   Here is a guide to help

 

 

[JoeS]

Interesting little tooth indeed, and agreed that it looks to be an indeterminate one.
Just to ad, the sheer number of denticles (mesial 48 / 5mm and distal 33 / 5mm, if that is correct) is well in range of cf. Richardoestesia gilmorei; however, denticle shape does not match that well either.(?)
Just out of curiosity, has anyone seen Richardoestesia gilmorei teeth with ridges?
I do have similar sized Acheroraptor teeth that stay well below these denticle counts, but it's possible that juvenile teeth are somewhat different.

[Troodon]

2 hours ago, JoeS said:

Interesting little tooth indeed, and agreed that it looks to be an indeterminate one.
Just to ad, the sheer number of denticles (mesial 48 / 5mm and distal 33 / 5mm, if that is correct) is well in range of cf. Richardoestesia gilmorei; however, denticle shape does not match that well either.(?)
Just out of curiosity, has anyone seen Richardoestesia gilmorei teeth with ridges?
I do have similar sized Acheroraptor teeth that stay well below these denticle counts, but it's possible that juvenile teeth are somewhat different.

 

Real small teeth have a much much higher density count so it gets pretty hard to compare data against juvie or adult teeth that are published.   They can also be mis-shaped depending on their growth stage and position.  So I guess juvie or infant teeth can be different since they go through an ontogenetic change like bones.   I'm also not convinced what we are seeing are ridges like Acheroraptor on such a small tooth, could also be a pathological.   We know so little of these dentitions so to be able to identify them to a specific species everything needs to line up to what is published, otherwise its indeterminate at least from me.  

I considered Richardoestesia gilmorei because of the high density you mentioned but everything I've seen published "that not being much" has the DSDI close 1 with rounded denticles so I did not consider them, why also a indeterminate tooth might be wrong .   Also I have not seen any with ridges the two morph types seem to be smooth...   

 

[jikohr]

3 hours ago, JoeS said:

Interesting little tooth indeed, and agreed that it looks to be an indeterminate one.
Just to ad, the sheer number of denticles (mesial 48 / 5mm and distal 33 / 5mm, if that is correct) is well in range of cf. Richardoestesia gilmorei; however, denticle shape does not match that well either.(?)
Just out of curiosity, has anyone seen Richardoestesia gilmorei teeth with ridges?
I do have similar sized Acheroraptor teeth that stay well below these denticle counts, but it's possible that juvenile teeth are somewhat different.

 

1 hour ago, Troodon said:

 

Real small teeth have a much much higher density count so it gets pretty hard to compare data against juvie or adult teeth that are published.   They can also be mis-shaped depending on their growth stage and position.  So I guess juvie or infant teeth can be different since they go through an ontogenetic change like bones.   I'm also not convinced what we are seeing are ridges like Acheroraptor on such a small tooth, could also be a pathological.   We know so little of these dentitions so to be able to identify them to a specific species everything needs to line up to what is published, otherwise its indeterminate at least from me.  

I considered Richardoestesia gilmorei because of the high density you mentioned but everything I've seen published "that not being much" has the DSDI close 1 with rounded denticles so I did not consider them, why also a indeterminate tooth might be wrong .   Also I have not seen any with ridges the two morph types seem to be smooth...   

 

 

On 12/19/2021 at 4:15 PM, ThePhysicist said:

I think your original thinking was correct. The longitudinal ridges on the crown faces and the apparent dissimilarity of the serrations on each carina are diagnostic characteristics of Acheroraptor. Would be nice to have measurements to confirm that as Frank requested.

Acheroraptor and other Dromaeosaurs can certainly have mesial serrations - the feature you're looking for is the difference in serration densities. Compare with this magnificent specimen of @JoeS's:

I've been giving this a lot of thought, especially since my modus operandi thus far has basically been post and hope the lord and savior of Hell Creek ID (aka Troodon) sees it and bestows his knowledge, but this is one of those rare cases where after reading the posts I slightly disagree and say Acheroraptor for the following reasons.

1. Seeing a picture of the serrations on the mesial and distal side the shapes genuinely look identical to me and the proportion is within the margin of error (there was some wear where I measured, I could have easily missed one or been off by one).

2. There's only a few things there described as having those ridges and the position of the ridges in the picture match the tooth.

3. The shape of the base is identical.

4. The slight differences in proportions seem to be the type I see just looking at different teeth that have been classified as the same species and are from different positions in the mouth (why yes I am a "lumper", thanks for asking).

I could very well be wrong, but the main reason I discounted Acheroraptor at first was I mistakenly thought it didn't have mesial serrations. now that I know it does and what they look like and see the exact numbers there is no question in my mind that's what it is. 

[TyBoy]

My vote would be also be indeterminate based on the denticles being chisel shaped which is not Acherorapter like Troodon said as well as being pretty upright.   Its also too small to be positive about those ridges.  Too much uncertainty to definitively identify it.  Nothing wrong with indeterminate.

Edited December 20, 2021 by TyBoy

[jikohr]

10 minutes ago, TyBoy said:

My vote would be also be indeterminate based on the denticles being chisel shaped which is not Acherorapter like Troodon said as well as being pretty upright.   Its also too small to be positive about those ridges.  Too much uncertainty to definitively identify it.  Nothing wrong with indeterminate.

What exactly is meant by "chisel shape" Like I said I just don't see the difference in the shape between the serrations pictured and the serrations on this tooth.

[Troodon]

Denticle shape is one of the characteristics we look at to ID a tooth, so when we talk about shape it's the very tip of the denticle we are examining.  Differences can be subtle.

 

So let's compare yours to a known Acheroraptor, the holotype and JoeS specimen

 

Evans makes the following comment about denticles in the holotype paper of Acheroraptor

"Posterior denticles are rounded but are very slightly asymmetrical and apically oriented"'

 

Comparing @JoeS to the holotype it's a perfect match..."rounded but are very slightly asymmetrical and apically oriented"

 

 

 

With your specimen the very tips are flat or chisel shaped, there are ones which are rounded.   They do not look overly worn.  Again, it might just be a stage of development but that's we have to go with.  It's an area of uncertainty and along with my other comments from above why I called it indeterminate.   It does not exclude it being an Acheroraptor.

 

 

 

 

Look its your tooth call it whatever you are comfortable with.   Everyone here has provided you their input to help you with that decision.

 

 

[jikohr]

21 hours ago, Troodon said:

Denticle shape is one of the characteristics we look at to ID a tooth, so when we talk about shape it's the very tip of the denticle we are examining.  Differences can be subtle.

 

So let's compare yours to a known Acheroraptor, the holotype and JoeS specimen

 

Evans makes the following comment about denticles in the holotype paper of Acheroraptor

"Posterior denticles are rounded but are very slightly asymmetrical and apically oriented"'

 

Comparing @JoeS to the holotype it's a perfect match..."rounded but are very slightly asymmetrical and apically oriented"

 

 

 

With your specimen the very tips are flat or chisel shaped, there are ones which are rounded.   They do not look overly worn.  Again, it might just be a stage of development but that's we have to go with.  It's an area of uncertainty and along with my other comments from above why I called it indeterminate.   It does not exclude it being an Acheroraptor.

 

 

 

 

Look its your tooth call it whatever you are comfortable with.   Everyone here has provided you their input to help you with that decision.

 

 

 

On 12/20/2021 at 5:22 PM, TyBoy said:

My vote would be also be indeterminate based on the denticles being chisel shaped which is not Acherorapter like Troodon said as well as being pretty upright.   Its also too small to be positive about those ridges.  Too much uncertainty to definitively identify it.  Nothing wrong with indeterminate.

Fair enough.

Thank you all so much for your help, I really do appreciate it!

Happy Holidays!

[Troodon]

Just an FYI don't expect to obtain any input from me any longer based on what I've seen with your auction listing.   I also see that you include COA.   Its one thing to identify a specimen in your collection one-way but very different when offered for sale with a guaranteed ID.    Not what would expect to see from a Forum member.