Mystery jaw - Maryland Potomac

[HemiHunter]

Found this cool little jaw fragment last week on the Potomac in a section that has mostly Aquia paleocene exposure but also has some eocene and miocene. There is a very tiny unerupted tooth in one of the sockets which I hope will help with ID. It's hard to get a good image but the tooth looks flattish with a rounded tip, not conical and not pointy. Any ideas?

[HemiHunter]

[HemiHunter]

Side view

[HemiHunter]

[HemiHunter]

[HemiHunter]

[HemiHunter]

End views

 

Edited February 7, 2021 by HemiHunter

[pachy-pleuro-whatnot-odon]

If I would have a wager, I'd say crocodile. That's based on:

• the carinae visible on the unerupted tooth;
• the thecodont condition of the teeth in the jaw, which matches both mammals and reptiles, but is absent in squamates;
• the fact that the tooth sockets are round and, thus, the roots are probably as well;
• the relatively large amount of space between individual tooth sockets; and, lastly,
• the relatively dense bone structure - or osteosclerosis - which hints at better adaptation to an aquatic environment.

[PaleoNoel]

@pachy-pleuro-whatnot-odon brings up some good points, however if it were croc I would expect more rugosity on a section of jaw, but in this case that texture may just be worn off. Also I would expect conical teeth from a standard piscivorous croc, however the unerupted tooth looks somewhat compressed. I believe terrestrial Boverisuchid crocs are not unknown in the aquia fm. (although if I remember correctly they've not been found in whatever member is exposed on the Maryland side of the potomac where D.P. and Purse are (could be wrong on that). All I'm saying is not to rule out large predatory fish. 

Cool find regardless.

[Anomotodon]

@pachy-pleuro-whatnot-odon did a great job of outlining key features that make this jaw archosaurian. I think a gavialoid is a likely possibility, based on how gracile this posterior dentary section is. Their teeth are often quite compressed and have defined carinae, especially in posterior position. I doubt it is a ziphodont crocodylian because their dentaries are much more robust and teeth have visible serrations. Also, rugose texture could be less pronounced in posterior mandible elements, especially in long-snouted (longirostrine) crocs, but also could have been worn down in this specimen.

[HemiHunter]

Thanks, @Anomotodon @PaleoNoel and @pachy-pleuro-whatnot-odon! You guys are amazing. I was hoping this might be crocodilian as it checks off one of my wish-list finds!  An awesome piece for my little collection.