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Identifying Theropod Teeth from the Hell Creek/Lance Fm


Troodon

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Updated March 29, 2023

Changed information on Avisaurus archibaldi

 

A few years ago most of the smaller theropod teeth from the Hell Creek/Lance Formations were identified based on teeth from the Campanian assemblages of North America. Over the past couple of years new discoveries have shed new light on the theropods of the end of the cretaceous and new species have been described. I have addressed these on separate topics but decided to put all of these together to get a better view of the current picture of the upper Hell Creek and Lance formations. If you see any omissions or errors feel free to let me know.

 

 

Tyrannosaurids:

Under Topic:

Identification Tyrannosaurid Teeth From North America - General Fossil Discussion - The Fossil Forum

 

 

Dromaeosaurids:

There are two described in the Hell Creek  Acheroraptor temertyorum and Dakotaraptor steini however there is mounting evidence that an additional one, mid-size, is present.

 

Saurornitholestes and Dromaeosaurus species are not present.  

 

Acheroraptor temertyorum

Identification: Like all Dromaeosaurid teeth the denticles are key and different between those on the anterior and posterior carinae. You should easily be able to see that the posterior ones are much larger. If the denticles are identical its probably a juvenile Nanotyrannus tooth. Secondly there are apicobasal ridges on the crown which are diagnostic to this species. There can be several on either side and fewer on posterior located teeth. The teeth are recurved and typically under 1/2" (13mm) long.

post-10935-0-83159200-1454681868_thumb.jpgpost-10935-0-12965900-1454681871_thumb.jpg

 

 

Dakotaraptor steini

Identification: 

 

 

Zapsalis sp. (UPDATE)

Identification: Similar to Z. abradens from the Judith River Formation.  Very compresses tooth with rounded serrations on the distal side and a smooth mesial edge.  One flat tooth surface with longitudinal ridges

 

This form of tooth has been identified as a premaxillary tooth on Saurornitholestes in Alberta.   So these teeth should most likely be assigned to Archoraptor but will need new discoveries to confirm it.

 

post-10935-0-02000000-1454683557_thumb.jpgpost-10935-0-55514400-1455624463_thumb.jpg.90330ff90e00e3b39cb21ccab2ae6375.jpg

 

Update:

The unserrated form of this tooth (paronychodon morph) may also be a premaxillary tooth of a Dromaeosaurid or Troodontid.  New discoveries are needed to properly assign it.

 

Troodontids:

There are at least two present  cf Troodon formosus and Pectinodon bakkeri. but only one described  Pectinodon bakkeri.

 

cf T. formosus is an easily recognizable tooth. Denticles strongly hooked and turned toward the tip

5a004b89dbf33_TroodontoothD91S.thumb.jpg.175c47145bf3833ebf439bb5d3b48a83.jpg

 

Pectinodon bakkeri significantly smaller 6mm or less than Troodon teeth. Comb like denticles on posterior carina, lacking on the anterior side..

Positionally these teeth have different morphologies can been see in the photo.

Pect1b.thumb.jpg.7ebed65f1a9d45990df9c97a12f84cc7.jpg.17e6c9b71ec278b4f1d94c31270708b2.jpg

 Reference from : Vertebrate Microfossil Assemblages by Sankey and Baszio

 

 

 

Other Teeth:

 

cf Paronychodon lacustris type teeth have several morph types are flat on one side and usually bear three or more longitudinal ridges.  Another morp type can be seen in the image. The other side is convex and can be smooth or longitudinal ridges can be present as well..

This is a tooth taxon so placement is questioned by many.  May be a Theropod or Pterosaur

post-10935-0-61975300-1455624499_thumb.jpg.16671b9fd492df114c93b1744fa21bcd.jpg

 

 

 

cf Richardoestesia gilmorei. 

 These teeth may have two different morphologies and can include a long form whose serration density is very high.  The information provided is the standard morphology.   What is shown comes from the Larsen/Currie's paper.  Data they used is from Longrich 2008.  Taxonomic placement of these teeth is uncertain.   Study included 33 teeth from the Lance & Hell Creek Formation - not all data was collected on these teeth

 

CH Avg: 5.9 mm (Range 3.6 to 10)

CBL Avg (14 teeth) 3.8 (Range 2.1 to 4.0)

CBW Avg (14 teeth) 1.5 (Range 1.1 to 1.8)

CBR: Avg (14 teeth) 0.40

CHR: Avg (33 teeth) 1.60

 

 

Density (16 Teeth)

Distal:  6.75 (5/mm) or 1.4 mm.   

Mesial: 9.4 (5/mm) or 1.88 mm

DSDI : 1.39

 

Other Characteristics

- Rounded small denticles

- Slight posterior recurve

 

Photo Scale Bar : 1 mm

Richardio.png.d402fed51f1746c59bfac3c48b850daa.png20230217_073841.thumb.jpg.5ae977a2421ff65f8abb909b46ccda8a.jpg

 

References:

Multivariate Analyses of Small Theropod Dinosaur Teeth and Implications for Paleoecological Turnover through Time

Derek W. Larson, Philip J. Currie 2013

 

Longrich NR (2008) Small theropod teeth from the Lance Formation of Wyoming, USA. In: Sankey JT, Baszio S, editors. Vertebrate Microfossil Assemblages: Their Role in Paleoecology

 

 

Richardoestesia isoceles.  

Typically are very compressed, elongated and form an isosceles triangle.  Fine serrations can be present

5a00474de0f13_RicardtoothD92D.jpg.40b1062e1ceb39a2191e0244d7bc05f8.jpg

 

 

This species along with the Paronychodon is currently under study and will most likely be described to a new taxon which may not be dinosaurian .

 

 

 

Albertonykus sp. is known from bones. Its teeth are very small and pointed. 

Photo of tooth is from the smaller Mongolian species Mononychus olecranus

 

Screenshot_20170805-143227.jpg.5d51a7edcc1e7569156bf416bfe5be94.jpg

 

 

 

Morph types isolated small theropod teeth are abundant in these assemblages. Morph types exist and determining the taxonomic affinities of these teeth is problematic. So be prepared to identify these teeth as Theropod indet.

Note A lot of what I've described here requires a detailed examination of the serrations. The crisper they are on your tooth the better the opportunity you will have to identify them. having some magnification capability helps

 

Bird: Avisaurus archibaldi

This tooth is typically sold as A. archibaldi.  Unfortunately this morphology of tooth is most likely Crocodilian per a recent publication, see attached topic.

1680089163409.jpg.b1af1b278723c83ebbc948705c5b6adc.jpg

 

A slightly different morphology pointed out in the paper is viewed as most likely Avian

 

Screenshot_20230329_042541_Drive.jpg.fcc55f833ceb555f4df2d238d5174934.jpg

 

IMG_6643.jpg

  • I found this Informative 24
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Regarding Pectinodon bakkeri I've observed illustrations of the teeth such as the image you've provided that suggest the tip of the tooth was rounded certainly by comparison to Troodon formosus. However the few photos I've found and the one specimen I've observed under magnification, of teeth attributed to Pectinodon, suggest a much finer tip. These teeth had large denticles only on the posterior edge of the tooth. Could this be explained by a variation in tooth morphology as is sometimes observed in other theropods? Or perhaps the teeth were misidentified although the absence of the Troodon type denticles from anterior portion of the tooth would suggest not? Any information you can provide would be appreciated and I thank you again for the valuable information you always provide!

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Good question. I've see both types and Ive attached a picture of each from my collection. Hope that's what you were referring to. I don't know if we are looking at positional variation or tooth morphology. The troodon maxilla I provided the ROM was their first look at any North American troodon tooth in a jaw so I have to believe little is know about T. pectinodon teeth.

Sorry for the poor quality images just used my phone. I should add the other image to my post.

post-10935-0-91961000-1454727265_thumb.jpgpost-10935-0-36442700-1454797208_thumb.jpgpost-10935-0-23203700-1454797213_thumb.jpg

Edited by Troodon
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It is what I was referring to. I can see it in the two pictures provided. It's an excellent comparison. Another fascinating dinosaur and I guess mystery to ponder.

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  • 2 weeks later...

Troodon, I'd like to add a correction if I may. The description for Paronychodon is correct, but the illustration provided is not.

True Paronychodon lacustris teeth do not have any serration denticles.

The illustrated tooth is actually Zapsalis abradens. These teeth are wider for to aft and have serrations on the distal/posterior edge and none on the medial/anterior edge.

Edited by hxmendoza
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That image came out of Dinosaur Systematics which was published in the early 90s. Agreed in 2013 that image was described to Z. abradens but only from the Judith River Fm. although there are affinities to those found in the Hell Creek. Like Paronychodon and R. Isoceles these tooth taxons are highly debatable and most will change when the research is concluded on the jaw that contains both morphologies. Thanks for the pickup.

Attached, not the sharpest images but you can see the different morphologies of these teeth from the Hell Creek.

cf Z.abradens

post-10935-0-55514400-1455624463_thumb.jpg

cf Paronychodon

post-10935-0-61975300-1455624499_thumb.jpgpost-10935-0-56813300-1455624579_thumb.jpg

Edited by Troodon
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Troodon, your two lower images are correctly true, non-serrated, cf. Paronychodon sp. teeth (at least until your jaw is described).

I have to disagree on you with your cf. Zapsalis tooth photo. That tooth is actually an anterior tooth (probably premaxillary) of Pectinodon bakkeri. Nick Longrich and I have discussed these teeth at length. Those denticles are far too large for Zapsalis. They are comb shaped and sharp. Zapsalis denticles are smaller and more box-like or chisel shaped with somewhat rounded tips.

Anterior and premaxillary teeth of Pectinodon do have varying degrees of vertical striations also. The tip of Pectinodon teeth actually becomes inclusive as being the first large denticle of the posterior edge, as we can see represented in your pictured tooth. This is also a distinguishing feature that separates Pectinodon from the cf. Troodon formosus teeth that are also found in the Hell Creek (though true Troodon formosus is only from the JRF).

The anterior Pectinodon teeth also can sometimes have subtle crenulations or rippling that appear to be failed denticles on the anterior/mesial carina of the tooth. This is evident also on your pictured tooth.

Zapsalis teeth have only a naked smooth anterior/mesial carina. Zapsalis teeth are also noticeably larger in size than Pectinodon teeth.

Attached is the page showing Pectinodon teeth from Longrich's paper on it. Your tooth resembles the first two illustrated teeth.

post-7726-0-43091800-1455636694_thumb.png

The next photos are of my true, cf. Zapsalis sp. tooth. This one is from the Hell Creek Formation. It is 16mm tall. Note the difference in denticle size and morphology.

post-7726-0-25147700-1455637097_thumb.jpegpost-7726-0-55365800-1455637066_thumb.jpegpost-7726-0-04986300-1455637140_thumb.jpegpost-7726-0-40556900-1455637168_thumb.png

Edited by hxmendoza
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Your correct. I initially thought that tooth was 1/2 inch. When I went looking for it it turned out to be 5mm and has to be Pect. Thanks for the correct image

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Your correct. I initially thought that tooth was 1/2 inch. When I went looking for it it turned out to be 5mm and has to be Pect. Thanks for the correct image

You're very welcome.

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Gentleman your opinion please on this tooth I own, would you identify as Troodon genus? Length is 11.2 mm, some worn serrations on the outer edge, thank you....

38049.jpg

Edited by Killclaw
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To contribute, here I have a Hell Creek tooth from Carter County of Montana. It's 2.62 inches in a straight line, bigger than some T-Rex teeth out there, yet its features remain distinctly Nanotyrannus.

post-4888-0-63927200-1455798132_thumb.jpg post-4888-0-16195800-1455798138_thumb.jpg post-4888-0-19966500-1455798142_thumb.jpg post-4888-0-14960600-1455798321_thumb.jpg

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Looking forward to meeting my fellow Singaporean collectors! Do PM me if you are a Singaporean, or an overseas fossil-collector coming here for a holiday!

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Andy thanks for sharing that beautiful tooth and it's partially rooted. Good example of a specimen at the high end of range for Nano teeth. Let's me add that Pete Larsen of the BHI agreed with the ID.

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  • 6 months later...

Updated the initial page to reflect the troodonitid genus change and added additional images and information.

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troodon... I have not seen the news on a genus change within the troodons.  Can you enlighten me and others?  Thanks. 

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