Thursday, April 9, 2009

Mystery fossil

Hello all,

Here's a couple bones I saw in a private collection over winter break, and these left the collector and myself stumped. I have no idea what on earth this thing is, but it looks mammalian.

Things to note: The concave part does look like an articulation, and the bones appear to be symmetrical. The larger of the two has some mud pellets cemented to it, so ignore those.

The part of the rock unit this is from is latest Miocene-Pliocene, and is generally devoid of sirenians. The usual suspects are pinnipeds and cetaceans.

I have seen a similar element at UCMP associated with an odontocete ulna, but nothing was said about the weird element.

Does this look obvious to anyone? I apologize for the colorful bedspread that served as my backdrop:


J. Velez-Juarbe said...

Interesting! It kind of looks like the proximal end of an ulna; but most likely not sirenian, nor desmostylian. I have the strange feeling I've seen something similar but can't remember when or where :S


Neil said...

I'll second Jorge. Certainly look like semi-lunar notch of the ulna to me. If so, the size and pronounced curvature makes me wonder if it isn't from some large terrestrial mammal? Or maybe a very lost sea sloth? (kidding)

Brian Lee Beatty said...

I agree, they look like proximal ulna fragments, but not any marine mammals I am familiar with. You might compare it with some of the pinnipeds from similar localities, but from what I recall of pinniped ulnae, they probably wont fit either.
It would be worth checking out some terrestrial ungulates and carnivores, too. Marine/non-marine mixes of faunas are not uncommon in the east coast, so it would be worth considering. In VA, Butch Dooley has found material of a large camelid with an articulated Diorocetus skeleton.
It is stuff like that that cause me to occasionally have doubts about exactly how aquatic desmostylians were.

Robert Boessenecker said...

Hey guys,

I'm positive it isn't a pinniped ulna, because I have proximal ulnae of an otariid and an odobenid from the Purisima, and have seen dozens of other pinniped ulnae at the San Diego NHM, and it isn't very similar.

I'm also hesitant to identify it as an ulna; both these specimens appear complete, and lack broken surfaces or surfaces of sutures. Additionally, the specimens are fairly symmetrical (the large one more so than the small one).

I wish I had gotten a photograph of the specimen at UCMP, although it wasn't identified, so that wouldn't be much help.

J. Velez-Juarbe said...

You're right Robert it doesn't look pinniped, I looked at some last friday at the NMNH. Lacking broken or sutural surfaces makes these fossils even weirder. Do you think is possible that broken surfaces have been eroded to look as if there were none?

Brian might be up to something, it could belong to a land mammal. I've found rodent fossils in limestones.


Dave Bohaska said...

Wish the specimens were in hand, but the fragment on the right looks like a porpoise skull fragment; vomer? On the bottom photo, part of the anterior wall of the cranial cavity is to the left. The back and medial walls of the two blowholes are just anterior (right) of that. Fragments like this turn up ocassionally.

Robert Boessenecker said...

J., There are some terrestial mammal specimens known (three horse tooth frags, and a camelid astragalus) from the same unit. I wouldn't be surprised.

Dave, Welcome! I thought there was some resemblance to an odontocete vomer, and I've found large, isolated vomers before. However, I have a partially disarticulated Delphinapterus skull handy, and the articular 'flange' on the mystery specimen doesn't appear broken/significantly abraded; additionally, there is no evidence of even a vestige of a vomerine canal.
Thus far, a very partial odontocete vomer is the best guess (not including indeterminate terrestrial mammal bone).