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Hell Creek jaws- hadrosaur or ceratopsian?


Parthicus

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I purchased these two fossils a while ago.  Both are from the Hell Creek Formation in South Dakota, and both were described as hadrosaur jaws.  They definitely seem to resemble the jaws of hadrosaurs, however I've noticed that the empty tooth rows of ceratopsians look extremely similar (to my untrained eyes), which is making me reconsider the seller's ID.  I am hoping that someone out there with more knowledge can state confidently if these are ceratopsian or hadrosaur, and preferably if they can briefly explain why they think so.  Bonus points if you can state if these are from the upper or lower jaws, or confidently state the genus.  (From my limited research, it seems Edmontosaurus is the only hadrosaur described for the Hell Creek in South Dakota; the most abundant ceratopsian is Triceratops, but Torosaurus is also possible, as is Tatankaceratops, and of course the always popular "not yet described".)  Let me know if additional photos would help your ID.

 

HC_jaw_1_1.jpg

HC_jaw_1_2.jpg

HC_jaw_2_1.jpg

HC_jaw_2_2.jpg

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Always difficult since both dentary specimens are fragments.  The tooth grooves are pretty shallow and close together so if I had to venture a guess would lean toward Edmontosaurus

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I think 'correct' is a push.  It is a matter of best guess rather than being right.  Edmotosaurus is a good guess.  Upper or lower... no idea.  

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  • 1 year later...

Sorry I’m late to this by a couple of years, but I also have some self collected elements from a Cretaceous formation. Based on what @Troodonsaid I’ll assume the one on the left is hadrosaur but might the one on the right be ceratopsian? It’s a little hard to tell, but the orange one on the right has noticeably deeper grooves than the one on the left

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BD0890B2-9415-46C2-99CE-DC5FE6D651DB.jpeg

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These are all very small pieces. Hadrosaurs have more teeth than ceratopsians and thus have slightly more and smaller tooth positions. But animals can be large or small as well. So, it's hard to use that as a measure.
I would agree and lean towards hadrosaur for the first two. Edmontosaurus is indeed the only hadrosaur described in the Hell Creek formation. But there are some reports of a potential lambeosaurine hadrosaur as well. Even so, the vast majority will be Edmontosaurus.
In some cases it might be possible to figure out if it's upper or lower jaw by looking at the angle and thickness of the bone. The lower jaw is much fatter than the upper.

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Olof Moleman AKA Lord Trilobite

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