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Found this fossil in a riverbed in Fannin County (North Texas) while hunting for fossils from the cretaceous period. (This is a follow-up from the same trip as my previous post - thank you to those of you who helped ID the mosasaur vertebra! And also thank you for correcting my terminology on mosasaur vs mosasaurus :BigSmile:).


I'm not totally sure what this is (at first I thought it was nothing too special - possibly just a very eroded Baculite as we were finding many of those in the area), but on closer inspection, there are fine striations on the fossil that make me think it is bone. My current guess (based on those striations and the longish/slightly curved shape of the fossil) is that it is a fragment of rib, and further, (based on the facts that everything else we were finding was from the cretaceous and that mosasaur are the only large marine vertebrate that I know of being regularly found in the area), that it is a fragment of mosasaur rib. However, I am not sure about this and am hoping for some more help on identifying what I've got here.


I hope these photos are good enough to see the details (i've tried to shoot them in half-decent light). If you zoom in, you can see the striations I'm talking about fairly well. (See dime for scale).


Here are both sides of the fossil



Here are the ends



And here is a closer shot of the more intact side



So in summary, I'm wondering if I'm right (or even on the right track) that this is a fragment of mosasaur rib? And following that up, whether ribs are identifiable by speciesm (probably not, but worth a shot :Wink1:)?


Final sub-question that is probably totally speculative, but I'm curious about: there are a lot of indentations and gouges in the fossil. Is it possible that these are marks from a predator and/or scavenger (e.g. sharks) chewing on the dead creature's carcass? Or is it more likely to just be erosion?


Thanks for putting up with so many questions!

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You are correct about it being bone, the cross section is another giveaway. Mosasaur rib is a likely possibility. Unfortunately, you won't get it to species level.


I'm guessing not all of the wear is just erosion, there is probably something from a biotic source as well. As opposed to predation marks and scavenger marks I'm thinking bio-erosion by borers such as bivalves. See examples from things such as shipworms, pholads, gastrochaenolites, etc.

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Welcome to TFF:)


Yep. Definitely some sort of bone. I agree that it looks like not all of the wear is just erosion, but I did not think about how it could be bio-erosion. Definitely could make sense.


No way to know what species it came from, but it is still a pretty nice find.  


Cheers and Shalom,



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