Identifying Theropod Teeth from the Two Med Formation

[Troodon]

Identification of theropod teeth from the  Two Medicine formation is always a challenge even for the more experienced collector. Sellers whether its a dealer or auction site also struggle with identifications and sometimes just shotgun it. So I decided to put this together as an quick aide in providing you some information. Among the sources used is the reference book Dinosaur Systematics by Ken Carpenter and Phillip Currie... its an excellent reference source. This aide is for the more common teeth collected and sold, not for more obscure theropods. I'm sure mistakes/omissions have been made, feel free to let me know.

Tyrannosaurs:

Tyrannosaurids in the JRF are not described but Daspletosaurus and Gorgosaurus are most likely present.    Teeth should be described as Tyrannosaurid indet.   Teeth around 4" are most likely Daspletosaurus sp.   Teeth from the TMF are either Daspletosaurus horneri or Gorgosaurus sp. see tyrannosaurid topic for details

Aublysodon a "nomen dubium" dinosaur and teeth being sold belong to one the other three Tyrannosaurs in these assemblages. They should also be labeled Tyrannosaurid indet. They are probably an early ontogenetic stage of these theropods in pre-maxillary teeth.

 

Dromaeosaurids:

Dromaeosaurus albertensis  Denticles (serrations) exist on both the anterior and posterior (inside the curve) carinae. The ones on the anterior are smaller than the posterior ones. You should be able to see the differences. The easiest way to identify these teeth is that the anterior denticles starts twisting towards the center of the tooth.

The serrations should look like these (scale .2mm)





cf Saurornitholestes langstoni  this is a very common tooth and small typically less than 1cm long. They are strongly recurved and sharply pointed, the cross-section of the base is rectangular and very compressed. The best way to identify these teeth is a great differences in size of the denticles, the posterior being larger. Also when observed under a scope the very tip of the  denticles are hooked towards the tip of the tooth.

The serrations should look like these (scale .2mm)






Others: several of these have not been described and are prefixed as cf (similar to)

cf Richardoestesia gilmorei  these teeth are quite varied in shape and size and are also common. Some are straight and others are slightly recurved. Denticles are often limited to the posterior carina and individual denticles are minute. If the denticles are present on both carinae they are identical in size.

The serrations should look like these (scale .2mm)





cf Richardoestesia isoceles  identical to R. gilmorei except they are elongated and form an isosceles triangle. This species along with the Paronychodon are currently under study and will most likely be described to a new taxon

cf Paronychodon lacustris type teeth are flat on one side and usually bear three or more longitudinal ridges. The other side is convex and can be smooth or longitudinal ridges as well. Zapsalis teeth are similar to Paronychodon but its a tooth taxon and may be dubious.

 

 

Zapsalis abradens is described from the JRF however recent publications from Alberta has shown this morphology to be premaxillary teeth of Saurornitholestes.   Zapsalis is not a valid genus.

 

Troodon formosus easily recognizable tooth. Denticles strongly hooked turned toward the tip.

Pectiondon sp. a Troodontid but significantly smaller 6mm or less than Troodon teeth. Comb like denticles on posterior carina, lacking on the anterior side.



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.


 

[MarcoSr]

Shark teeth serrations can also be diagnostic but coming from a marine environment it doesn't take much water wear to change the look of the serrations. Even pristine looking shark teeth can have water wear which can alter the serration tips. Do you see any water wear in the teeth from the Judith River and Two Medicine formations that could alter the serration tips and confuse the id based upon serrations?

Marco Sr.

[Troodon]

Yes to answer your question. I find it interesting that when I look to identify a shark tooth the root plays a important part of that identification. However with theropod teeth its all about the crown even though the root makes up the greater part of the tooth, it has no bearing on the ID and most found are shed teeth.

Several things come to mind that alter theropod teeth can confuse ID. One is natural wear. Even though a theropod replaces its teeth its not anywhere at the same rate as sharks and the denticles can be reduced. Wear facets are another natural wear feature and often found on teeth through the grinding of the upper and lower jaw. Facets are often seen on the side of the tooth but can appear on the edges removing the carina with all of its serrations. The other is water. Theropods have a ball feeding at river beds during a flood stage where hundreds of herbivores have drowned. So channel deposits are a great place to collect and worn teeth with minimal or no serrations are common.

[fossilsonwheels]

Very informative. Thank you for posting this @Troodon . I am starting my search for a Dromaeosaurus tooth so I found this quite helpful. It gave me an idea of what to look for.

[Fossil Maniac]

Under what magnification is this?

[Troodon]

5 minutes ago, Fossil Maniac said:

Under what magnification is this?

What are you referring to?

[Fossil Maniac]

On 5/16/2022 at 10:44 AM, Troodon said:

What are you referring to?

The images of the Dromaeosaur teeth under the microsope.