Saturday, March 27, 2010

Pinniped ancestry: the "Oligocene Seal" from South Carolina





Putative seal femora from the Late Oligocene of South Carolina, from
Koretsky and Sanders (2002).








Morgan said...

well, the biggest problem with the with pinniped nonmonophyly is that you have to absolutely ignore every single genetic analysis EVER DONE for it to work. That's a little hard to swallow.

IIRC, Koretsky also didn't really compare the partial bones to a wide variety of carnivorans, fossil and modern. It would not surprise me at all if this fossil had nothing to do with pinnipeds.

Robert Boessenecker said...

Yes, that is definitely the single worst problem with pinniped diphyly or paraphyly. Which, if you read some more recent work by Koretsky (i.e. Koretsky and Barnes 2006), ignoring molecular analyses is effectively what they've done.

Yet another thing I forgot to elaborate on: I wouldn't be surprised either if those femora were from some completely different carnivoran group.

J. Velez-Juarbe said...

I am not as well acquainted with fossil pinnipeds as with other marine mammals (though maybe I should), but it seems that Enaliarctos had a fairly derived morphology for a Late Oligocene critter. What I want to say is that finding Late Oligocene Enaliarctos and the phocid femur on opposite sides of North America, doesn't necessarily imply different origins (diphyly). It can also mean a much earlier divergence between the two groups and rapid dispersal (Caribbean seaway?!). There is definitely a need to get better samples from rocks of the right age (Early Oligocene).
There are indeed some discrepancies as to the provenance of the South Carolina fossil. Also there were other morphological features of those femora that could have been discussed in the paper.

Morgan said...

Indeed...It wouldn't surprise me if Enaliarctos is more closely related to otaroids than to phocids. My guess is that the true ancestral pinniped are going to be Early Oligocene in age (and possibly arctic in distribution).

Brian Lee Beatty said...

I agree with Jorge, this is not a decisive fossil, and I also agree with Morgan and Bobby that this might not be a phocid at all. I remember when Irina was showing me this specimen and I was hard pressed to get a clear discrete character from her that she could say made it a phocid and not another carnivoran - but, either way, there is much, much more that needs to be found. Speaking of which, I hope to be tackling some Late Oligocene of the NE very soon... heheheheh...

Robert Boessenecker said...

It'll be difficult to find more Arctic critters aside from Puijila, I'll wager, but it's a fascinating possibility - an early Oligocene Arctic origin could explain (as Rybcynsky et al discussed) could explain the early phocid/everything-else split.

Brian: Late Olig. of the Pacific Northwest?

Jorge: Perhaps there are more Early Oligocene rocks in New Zealand (not helpful if pinnipeds didn't reach the S Pac. until the Miocene, though) and Japan; some rapidly subsiding basin from that time must have a good record of it.

Robert Boessenecker said...

I believe the Alsea Fm. in Oregon/Washington (type area of Simocetus, and Mark Uhen's new edentulous mysticete from the Emlong collection that's more basal than Eomysticetus) is Early Oligocene; there are plenty of late Eocene rock units (which have yielded potential archaeocete teeth) and more than enough Late Oligocene units; I bet there's something Early Ol. up there.

J. Velez-Juarbe said...

There are some neat Early Oligocene formation in Puerto Rico, those and the Late Oligocene ones are actually where I collect most vertebrate fossils. The Early Olig. was colder even in the Caribbean; so who knows, it might be a possibility.

As for the Pacific NW, there sure must be some Early Oligocene there (other than the Alsea), but it seems so hard to look for fossils there. I was really disappointed last October when I was in Oregon. Emlong must have been really persistent to be able to find all the material he collected. Fortunately, I think that some of his unprepared material at the USNM will finally see the light of day in the coming years.

Erich Fitzgerald said...

Koretsky's 'Late Oligocene phocid': hmmm. Pretty ambiguous to me given that there is a 50/50 chance it is derived from late Neogene/Quaternary strata that unconformably overlie the Paleogene sequence in Sth Carolina.

As for SW Pacific options for early pinnipeds: no firm pre-Late Miocene record. I currently have a student writing up the Mio-Pliocene 'monachine' material from Australia (reported in Fordyce & Flannery, 1983), and I am working on a recently collected Late Miocene skull from this part of the world.

Robert Boessenecker said...


Yes, the stratigraphic provenance of those specimens is another issue, at least Jorge has mentioned the same to me. Another issue is this: those units are very thin, and during my thesis fieldwork, I've documented marine bioturbators reworking bones and other clasts up to two meters below their original horizon, and it very well could be much more than that. So, "backwards" reworking is possible as well, especially in cases of thin stratigraphic units.

Glad to hear that someone's working on southern pinnipeds again! Remind me about this and I'll email you pictures - there's a collector in New Zealand who's collected some pinniped material (including a complete phocid braincase) from Taranaki - I'm not sure how much material is already in museum collections, but F.Y.I.