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Pachycephalosaurid/Thescelosaurus Tooth Identification


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One of the more frequent questions I get asked is to identify teeth from Thescelosaur's and Pachycephalosaurid's since they are so similar in appearance.

So when I run across a paper that has anything associated with it, I'll take a look. Recently I read a 2014 paper by Clint Boyd of the School of Mines in SD, that described skull of Thescelosaurus neglectus from the Hell Creek Formation, with some nice photos of the dentition's. It motivated me to do some additional research to get a better understanding of these teeth using scientific papers instead of anecdotes, supplier listings or my perceptions which I found out were incorrect. My resources being limited I did not find much out there in the public domain and read that little is know especially with Pachycephalosaurid's dentition's. So I'll present what I found and hope there are members of this forum that have access to additional information that can enlighten us.

The dentitions of these two families of dinosaurs are heterodontid so the jaws contain different tooth morphologies although some species of Pachy's may not be. To my surprise, the book Dinosauria (2nd ed) states that dentary teeth (from the mandible) from Pachycephalosaurid's are only known from a few species and only Stegoceras from the HC and LC formations. Not sure if that statement is still valid, the book was published in 2007.

Thescelosaurus neglectus

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Premaxillary Teeth (pm1-6)

There are 6 teeth in each Premax. The photo gives you a great image of what they look like, all are bulbous in shape with some curvature in the crown. Also added an isolated tooth, two views from my collection.

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Maxillary Teeth (mt1-20)

There are 20 teeth in each maxillary and take a spade shape. They are compressed, the crown is ornamented with fine ridges from the tip to the base. The more posterior the tooth the larger the wear facet and the tooth takes a different look, looses it's pointed tip. The first photo one can see all of the premaxillary teeth in "A" the anterior teeth in "B" and posterior teeth in "C". I also added a couple of additional pictures isolated teeth one anterior and one posterior

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Dentary Teeth (dt1-20)

The teeth on this skull are poorly exposed see photo below (dt1-7) on one side and only the first three (dt) are visible on the other but they appear to take the shape of smaller but not as robust premaxillary teeth. Since the dentary teeth in this skull so not provide us a good view I used another source Sternberg 1937 paper. In this image only # 8 is a dentary tooth, 1 & 2 are premaxillary, 4-7 are maxillary. The main difference between this and a maxillary tooth is a much more pronounced center ridge near the center of the crown. These teeth are larger than maxillary teeth with a crown that is higher and more pointed. I also added a couple of isolated teeth from my collection.

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Paper : The cranial anatomy of the neornithischian dinosaur Thescelosaurus neglectus

by Clint A. Boyd

Edited by Troodon
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Pachycephalosaurid

One way to approach this is that if it does not fit Thescelosaurus tooth morphology its most likely to be a Pachycephalosaurid :)

These teeth appear to take different forms depending on species but seem to be more robust than Thescelosaurs. The vertical ridges are more pounced, fewer and a more prominent center ridge may exist.. There is also no symmetry with the crowns.

Here are some example

Teeth of a Stegoceras validum from the Hell Creek

Top row are premaxillary, second row maxillary (C & D), Third row anterior dentary (E & F) and Bottom row posterior dentary (G & H)

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Isolated maxillary tooth from a Pachycephalosaurus wyomingensis

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Isolated tooth Pachycephalosaurus wyomingensis from Smithsonian

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Sketches of isolated teeth Pachycephalosaurus wyomingensis

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Maxillary teeth of Dracorex hogwartsia

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Isolated teeth from my collection and others

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Although I did not find any papers on nipper (incisors) teeth most skulls contain them. The teeth can be serrated or non serrated. Do not know if these are just part of the pre-maxillary dentition or if they are also exist in the mandible. The skull of Dracorex does not have any premaxillary tooth sockets.

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Only two species known from the Hell Creek has depicted in this illustration  by Nobu Tamura

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Dracorex_hogwartsia

Fantastic post! This is right up my alley. Without a doubt one of my favorite teeth. I read this paper when it came out and was hoping that it would finally put to rest the pachy/thescel tooth confusion. Unfortunately for me, it did not! When it comes to Thescel maxillary teeth, I think we can positively identify now what that tooth looks like. Unfortunately, that isn't so with the dentary teeth. Pachy teeth and Thescel dentary teeth still look very similar to me. So much so, that I am still not able to tell them apart. They both seem to have that very strong medial ridge running down the center of the tooth. To me, the photo you provide of your thescel maxillary tooth in the left picture and the photo's you show of pachy teeth look the same to me. I've been looking at all my teeth that have that strong medial ridge and I have quite a few and there is no way I could tell you which is a pachy and which is thescel. I don't know if size would be a factor. I have some teeth that are larger than others but they may just be an age difference. To me in all other respects they look the same. I still don't have a proper camera yet but I'll try and post some pictures soon of some of my teeth.

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Fantastic post! This is right up my alley.

Unfortunately, that isn't so with the dentary teeth. Pachy teeth and Thescel dentary teeth still look very similar to me. So much so, that I am still not able to tell them apart. They both seem to have that very strong medial ridge running down the center of the tooth. To me, the photo you provide of your thescel maxillary tooth in the left picture and the photo's you show of pachy teeth look the same to me.

Well that's what I thought but if you look at Sternberg image 8 and your teeth are symmetrical with a strong central medial ridge they are probably Thescelosaurus. Will have a look when you get those images posted.

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Here is a plate of Pachycephalosaurid's teeth from different localities. Very different than Thescelosaur. Crowns can be more asymmetrical, triangular versus spade and the center ridge is much more prounced. The fine vertical ridges that are present with Thescelosaur teeth do not exist.

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Dracorex_hogwartsia

post-13649-0-75904500-1459547900_thumb.jpgpost-13649-0-59697000-1459547931_thumb.jpgHere are a couple of teeth that I think show pretty well the two different looks that these teeth have. What do you think Troodon? Are these from the same dinosaur? Pachy or Thescel?

Edited by Dracorex_hogwartsia
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Based on what I presented the one on the left is a dentary tooth and the other maxillary tooth of Thescelosaurus

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Dracorex_hogwartsia

Both of these teeth have always been called Pachycephalosaur teeth by most every dealer I've ever dealt with. That's what both of these teeth were sold to me as by the same dealer even though they obviously look different. If the tooth on the left isn't a Pachy tooth, then I don't think I own one. To me, my tooth on the left looks exactly like the plate of Pachycephalosaur teeth you posted from the different localities. My tooth on the right I think is definitely a Thescelosaurus maxillary tooth. I own a lot of these teeth but the bottom line may be that the differences are just too subtle for me to distinguish because all the pictures you have posted of pachy and thescel teeth all look the same to me.

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Susan from PA

I would assume that my search for a Pachycephalosaurid tooth continues, as this look very similar to the one that Dracorex hogwartsia posted above on the left.

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Dracorex_hogwartsia

I would assume that my search for a Pachycephalosaurid tooth continues, as this look very similar to the one that Dracorex hogwartsia posted above on the left.

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What you have is what virtually everyone describes as a Pachycephalosaur tooth. It's been that way for the past 20 years. The question is, is it really or is it actually a Thescelosaurus tooth. Troodon as usual, has done a fantastic job of showing us pictures and descriptions of the different teeth. My problem, is that I still can't tell the difference between a pachy tooth and a thescel dentary tooth. A thescel maxillary tooth looks completely different and I think is easy to identify. I will probably still continue to call what you have a Pachycephalosaur tooth.

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I would assume that my search for a Pachycephalosaurid tooth continues, as this look very similar to the one that Dracorex hogwartsia posted above on the left.

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Can you take another picture outside the case, more light and sharper. Hard to see a crisp clear image to compare against.

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Both of these teeth have always been called Pachycephalosaur teeth by most every dealer I've ever dealt with. That's what both of these teeth were sold to me as by the same dealer even though they obviously look different. If the tooth on the left isn't a Pachy tooth, then I don't think I own one. To me, my tooth on the left looks exactly like the plate of Pachycephalosaur teeth you posted from the different localities. My tooth on the right I think is definitely a Thescelosaurus maxillary tooth. I own a lot of these teeth but the bottom line may be that the differences are just too subtle for me to distinguish because all the pictures you have posted of pachy and thescel teeth all look the same to me.

I have the same issue you do, that some of these teeth have been treated one way for many years but that does not make it right. Suppliers are a poor choice to fall back on because they are going to take the easiest path for profit and very few research papers. I've presented some examples and interpret them as you please.
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Susan from PA

Here are some better pics, Troodon. Hope this helps.

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Susan from PA

The beautiful thing about collecting fossils is that it is science, and science is always changing. There are new species discovered every day, and papers written on these organisms. How many collectors looked through their theropod teeth hoping that they might have a Dakotaraptor tooth? I know I did, and even though I didn't have one, it was still fun to look. In this case, rather than a paper written about a new species, it's one written about an old friend. Sometimes, this new information compells us to make a change in the identification of one or more or our specimens. Pachycephalosaurs are some of my favorite dinosaurs, but if the tooth I have belongs to a Thescelosaurus, then it does, and my quest to find a Pachyceohalosaur tooth will continue.

I can speak from personal experience that most dealers make errors in identification of their specimens. I know because I've lived through it, and Troodon along with me. I thank the good Lord every day that I found this forum. I've had everything from misidentified teeth to something sold as a femur that is in fact a very large tibia. A month ago, we identified this tooth as Pachycephalosaur, but if new scientific information changes that identification, then so be it. Believe me, there is nothing more painful to a collector than thinking you purchased a juvenile T.rex humerus, having an email from a paleontologist stating the same, only to learn that it indeed belongs to a Thescelosaurus. Yes, that happened to me as well. I said a few choice words, and changed the label in my collection. Then I thought to myself, " it's a really nice specimen, it's from a dinosaur, and I learned something new. . How awesome is that! " :).

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Thanks for the additional photos. To me it looks exactly like the one in Sternberg photo #8, dentary of a Thescelosaurus. A defined medial ridge from the tip to the base with strong ornamentation on either side. I did call this a Pachy before I read Sternberg's and the 2014 paper.

On 8 do you see how the medial ridge fans out at the top, just like your tooth. Dead ringer

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Should have posted these photos in my initial posts.

I happen to have a few jaw sections with unerupted teeth that I thought were Pachy but are clearly Thesc, here are two. Wish I was wrong because Bonehead material is one favorite 😆 and Thesc is near the bottom 😝

It's definitely a mandible and the tooth poking it's crown up fits all of the characteristics of a dentary tooth. This jaw section has 5 teeth.

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Same on this mandible section with 2 teeth

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Edit: let me add that after recognizing that the teeth in the jaw sections were not what I thought they were I compared them to mandibles of Pachy and Thesc and came away with the conclusion they compare very well with Thesc.

Edited by Troodon
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Yes, that happened to me as well. I said a few choice words, and changed the label in my collection. Then I thought to myself, " it's a really nice specimen, it's from a dinosaur, and I learned something new. . How awesome is that! " :).

Ha ha boy have I've done this so many times on the same specimen. I learned to keep all my labels on Word so all I have to do is change the name. It is indeed part of collecting fossils that are not fully understood. You just have to look at the Hell Creek that has material which is readily available but in reality is poorly understood. Just look at all the teeth that have had new names attached to them over the past few years.

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Susan from PA

Well, I must agree with your assessment, Troodon. My tooth is indeed a Thescelosaurus dentary tooth. I write my labels in pencil, so it was easily changed. There is, however, a silver lining, as my collection is not completely devoid of Bonehead specimens. This specimen below does not belong to a Thescelosaurus. If in your future research you find that it does, please send me a PM before you post. I'll need to consume a few adult beverages prior to changing the label. ;).

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You are very fortunate it's April 2....

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Dracorex_hogwartsia

Troodon, I was wondering if you could do me a favor, could you please take a picture of a pachy tooth and a thescel tooth directly side by side so that I can get a better comparison. I swear, I don't see the difference that you and others see. I think my brain operates differently than others. My brain see's the similarities not the differences. Thank you.

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Dracorex_hogwartsia

Troodon, never mind. A friend of mine has helped me see the difference. For me it's subtle but I can finally differentiate between the two. For years, this tooth was on the top of my collecting list. I bought every beautiful example I could find and have a very large collection of them. It appears that out of all the teeth I have, I may actually only own one Pachycephalosaur tooth, maybe. Every other tooth I have looks to be a Thescelosaurus. Really makes since when you think about it. Pachycephalosaur remains are very rare. Thescelosaurus remains are not.

One thing that still confuses me though are the incisors. If virtually all the teeth I own are actually Thescelosaurus and maybe just one is a Pachycephalosaurs, why do I have so many incisors if they belong to Pachycephalosaurus.

Edited by Dracorex_hogwartsia
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Well the same thing happened to me and I'm sure many other collectors, everyone thought those dentary teeth were Pachy and were sold that way. Well I've not seen any paper that ties those big fat incisors to Pachy. My only evidence is looking at skulls at shows or BHI. To complicate matters Sankey (2008) attributes this tooth to a Troodon incisor, see Figure 3.(13-16). It fits the serrations characteristics but seems kind of fat and big for one. However other than my maxilla there has been no cranial material found of troodon. Still an open question like many others but I still think it Pachy.

By the way very little Pachy material has been found in the HC and most all of the Pachy material (bones & claws) you see sold on auction sites and dealers is actually Thescelosaurus, sorry to say.

sankey -HC theropods.pdf

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Dracorex_hogwartsia

Well fortunately for me, I didn't buy all these teeth because they were Pachycephalosaurus. I just love these small leaf shaped ornithischian type teeth. I don't care what they are. Having said that, I will be paying a lot closer attention to them now.

Of all your pictures, the teeth that I find the most interesting are those of Stegoceras. Especially the anterior dentary teeth. I can say without a doubt, that I do not own this tooth. This is one species I will be keeping an eye out for.

Edited by Dracorex_hogwartsia
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We all need to pay attention. I need to go through all my teeth and see if any are Stego. Remember it's half the size of an adult Pachy/Thesc so the teeth should be smaller.

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Dracorex_hogwartsia

We all need to pay attention. I need to go through all my teeth and see if any are Stego. Remember it's half the size of an adult Pachy/Thesc so the teeth should be smaller.

That's good to know. Thanks!

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  • 5 months later...

Tomas Carr  book shows some clear examples of these teeth.

 

 

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This is the first publication where this canine tooth has been attributed to Pachycephalosaurus wyomingensis 

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Thescelosaurus canine premaxillary/canine teeth.  One morphology shown is new to me and one I've never seen.

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