Thursday, April 23, 2009

Puijila, a very basal 'pinnipedimorph'

Its been a very busy week for me, and since I finished my proposal tonight, I thought I'd spend some time on a long-ish post. Its been an exciting day. Aside from the obvious (i.e. the topic of this post), today saw the release of the most epic PALAIOS issue ever:

Peters et al. 2009. Sequence stratigraphic control on preservation of Late Eocene whales and other vertebrates at Wadi Al-Hitan, Egypt. PALAIOS 24:290-302.
Ehret et al. 2009. Caught in the act: trophic interactions between a 4-million-year-old white shark (Carcharodon) and a mysticete whale from Peru. PALAIOS 24:329-333.
Nielsen, 2009. Pliocene balanuliths from Northern Chile: The first report of fossil balanuliths. PALAIOS 24:334-335.

The first of these is basically 100% relevant to my master's thesis; the second wasn't too exciting, and the third - well, I'm keeping that on the D-L for now.

Without further adeu, I am very pleased to present Puijila darwini, a very early 'pinniped'. I was extremely excited to read this paper, as was my colleague Morgan Churchill, whose enthusiasm was much shared via facebook. The two of us are some of the only paleontology students in the U.S. studying fossil pinnipeds (ironically both from landlocked states; the last sea in this area was the Cretaceous-Paleocene Cannonball Seaway).

As you can see, this is a pretty cute little critter. It has short-ish fore- and hind-limbs, a complete arctoid dentition (i.e. the postcanine dentition is not simplified as in later-diverging pinnipeds), a wide otter-like skull, large infraorbital foramina, robust forelimb bones (the humerus in particular) which have large muscle attachment areas, flattened phalanges, and an elongate tail.

Before I delve further, a little taxonomy/phylogeny. Pinnipedia (as you surely know) includes the modern walrus, sea lions, fur seals, and true seals. Following the phylogeny of Berta and Wyss (1994), most modern and fossil 'pinnipeds' comprise the clade Pinnipedia. The Pinnipediformes is a slightly more inclusive clade that includes the basal taxon Pteronarctos. The Pinnipedimorpha is an even more inclusive clade that includes the Pinnipediformes + Enaliarctos. Recently, Wang et al. (2005) included the basal (semiaquatic at the very most) arctoid Amphicticeps within the pinnipedia - obviously a much more inclusive use of the clade than Berta and Wyss.

The oldest known pinnipedimorphs are Enaliarctos tedfordi and Enaliarctos barnesi from the Oligocene (Chattian, 29-23 Ma) Yaquina Formation of Oregon (Demere et al., 2003). These appear several MYA before Puijila, already fully marine, and with significantly more marine/aquatic adaptations (larger infraorbital foramina, more enlarged forelimb bones, shorter hindlimbs, clearer progression toward homodonty, reduced tail, enlarged 1st metacarpal and 1st and 5th metatarsals, etc.). Because of this, Rybcyznksi et al. (2009) regard Puijila as a relict taxon.

Two very intriguing implications of this study arise from the location and geologic context of this critter. For starters, this fossil is from Nunavut - specifically, Devon Island, well above the arctic circle. The authors state that this may indicate an arctic ocean origin for pinnipeds. This is fine, except for Enaliarctos occurring in the North Pacific in a far more advanced 'form' several million years before. Demere et al. (2003) predicted the center of origin for pinnipedimorphs to be the North Pacific. It is certainly possible that this is perhaps a function of collecting bias, and that other Oligocene marine units worldwide need to be prospected and more greatly scrutinized (i.e. New Zealand, Australia, Argentina, India (?), and Japan). In any event, the Demere et al. hypothesis is certainly still possible, and likely more parsimonious as 1) the later occurrence of Puijila in the arctic may be a function of dispersal from the North Pacific and 2) there are other similar taxa (i.e. Potamotherium, Amphicticeps) from Europe and central Asia.

The second implication is that Puijila is from lacustrine deposits, and thus was likely semiaquatic. The pre-Enaliarctos pinniped record was effectively nonexistent, and gave no hint at the transition from land-to-sea. The cetacean and sirenian fossil records, however, have a clear transition from 'amphibious' taxa (Pakicetus), semiaquatic taxa inhabiting freshwater (i.e. the "crocowolf" Ambulocetus), semiaquatic marine taxa (protocetids such as Maiacetus and Georgiacetus) and fully (permanently) marine taxa (basilosaurids such as Basilosaurus and Dorudon). However, Enaliarctos is clearly marine in terms of its adaptations and associated depositional environment. In the case of Puijila, however, the associated sediments are lacustrine, and the adaptations are very 'otterlike'.

Additionally, the phylogenetic position of Potamotherium as a pinniped in this analysis is very interesting, as this taxon has traditionally been interpreted as some kind of musteloid, and in the past used as evidence for a true seal-mustelid link (which is a load of B.S., and I'll post about that in the future). Short version: I really, really liked this paper. I first heard about this critter at SVP, although someone told me instead that it was a very early otariid (fur seal/sea lion).

Addendum: I forgot to mention this in my original post, but Tedford et al. (1994) conducted a phylogenetic analysis of the arctoidea when they described new material of the 'beach bear' Kolponomos (a topic for a post of its own, because it is far weirder than Puijila could ever hope to be). Kolponomos is an ursid-like critter, with forward pointing eyes, and very wide/large sea otter-like teeth presumably for crushing mollusks, and postulated to inhabit the intertidal zone. It is known thus far only from shallow marine rocks. Kolponomos is from the late Oligocene and early Miocene of the Olympic Peninsula, and I know at least from the Clallam Formation. In any event, at the time Kolponomos plotted out as the sister taxon to pinnipedia, another intriguing hypothesis. I think future analyses, especially ones investigating pinniped ancestry within the arctoidea, should also include Kolponomos. If Kolponomos is in this group of pinniped-like arctoids as well, it would certainly paint a more convoluted picture (i.e. both freshwater semiaquatic and coastal semiaquatic 'proto-pinnipeds'. Anyway, I really need to get to campus to print off Wang et al. (2005), do some touch ups on my master's proposal, and finish my presentation on Purisima Formation odontoceti.

9 comments:

Morgan said...

I kind of "thought" about an arctic center of origin last year. While it doesn't fit into the Enaliarctos data (and yes, one fossil a center of origin doesn't make), it does work for at least one good reason. It would explain the weird and sudden appearance of both phocid subfamilies in the Mid Miocene, in the Atlantic. If that group had it's center of origin there, it would explain the gap quite nicely, and make biogeographic sense

The phylogeny is interesting, however it would have been nice to include more fossil and modern pinnipeds. As is, it's difficult to tell where exactly Puijila falls, especially since the author seem to want to "ratchet" up Enaliarctos as just an ancestor to Otariids and Odobenids, and not phocids.

At least there is now hope that maybe we can find some stem pinnipeds closer to home...

J. Velez-Juarbe said...

Enaliarctos tedfordi and E. barnesi are the best known Chattian pinnipeds, but there's also the "Oligocene seal" of Koretsky & Sanders (2002) from Chattian age deposits in South Carolina, which according to them is a Phocidae. This seems to favor a Late Eocene/Early Oligocene Arctic origin for pinnipeds.

Koretsky, I. A. & A. E. Sanders. 2002. Paleontology of the Late Oligocene Ashley and Chandler Bridge Formations of South Carolina, 1: Paleogene pinniped remains; the oldest known seal (Carnivora: Phocidae); pp. 179-183 in R. J. Emry (ed.), Cenozoic Mammals of Land and Sea: tributes to the career of Clayton E. Ray. Smithsonian Contributions to Paleobiology 93.

Robert Boessenecker said...

Hey Morgan,

I certainly agree about the arctic C-O-O explaining the phocid appearance. We just need some older fossils from Oligocene strata up there - someone really needs to go to the Cornwallius type locality in Alaska to look for pinnipeds, I think.

I definitely agree about a broader analysis - at the very least including 'basal' taxa like Proneotherium/Neotherium, Desmatophoca, Thalassoleon, some phocids, and some extant critters. I was pretty dissappointed that they didn't include Kolponomos in their analysis, which according to Tedford et al. 1994, is the sister taxon to pinnipeds.

I didn't catch the 'otarioid' thing (although I'm sure they didn't use that term), but I'll look through there again; Richard Tedford is a coauthor on the paper anyway. And it is definitely sorta depressing to think that the closest pinniped fossils to hear may be in the subarctic...

Jorge - I don't really buy for one minute the 'phocid' seals from the Chandler Bridge Fm. of SC. After all, those specimens are just proximal femora. I think someone really needs to redescribe them, and compare them with Enaliarctine femora, and basal odobenid, otariid, and desmatophocid femora, and a broader swath of extant pinniped femora. Additionally, they should now be compared with Potamotherium (which they may have done) and Puijila.

Neil said...

I was a little puzzled that they didn't include any extant pinnipeds in their phylogenetic analysis. The methods section states "the emphasis on basal arctoids aims to avoid the effects of long branch attraction." But then why were Mustela, Lontra and Ailurus included? I realize it's not possible to entirely lay out detailed methodology in a Nature paper, but I haven't much in the way of details on why these taxa were included in the supplementary info, lots of other cool stuff in there though.

Also I know I am beginning to sound like a broken record, but given previous suggestions of a relationship between Kolponomos and Amphictis, and the marine habits of the former, it would have been interesting to see Kolponomos in the analysis as well. I've pondered blogging about this but I think I stick with the Abu Ghraib/dick jokes...wouldn't want to get myself in trouble or offend anyone.

Neil said...

Ha spent an hour writing that previous comment, Bobby beat me to the punch!

Brian Lee Beatty said...

Also, did anyone else notice that Potamotherium, which has previously been considered a basal otter (Carroll 1988) or an oligobunid (Wang et al ??), is here considered a pinniped ancestor too?
What is also lacking from this analysis are most modern and fossil otters. I wonder if they would get a different result if they included Aonyx, Pteroneura, Amblonyx, or even Enhydrotherium?

J. Velez-Juarbe said...

Hey Robert,

I was talking to a friend on Friday about the SC phocid, and what he was telling me was that there might be some uncertainties about the stratigraphic provenance of the specimens (I later saw that this is also mentioned in Deméré et al., 2003). I wrote a critique about the paper describing the phocid femora about 2 years ago, but I can't find it in this computer or remember what I wrote :S

And about Puijila lets hope that a more thorough analysis, with more taxa, appears soon.

Robert Boessenecker said...

Hey Guys,

I'm probably just going to continue on posts with Puijila, and early pinniped evolution; its a fascinating subject, and after my thesis committee meeting tommorrow, it is something I really should read up on more (i.e. especially Berta et al. 1989, and Berta and Ray 1990/1).

In any event - Jorge, I'm not surprised. I really think someone should re-analyze those fossils and compare them with contemporary arctoids. Maybe something I'll do in the future, who knows. I would be a hell of a lot less skeptical if there was something other than a partial femur (i.e. a partial skull or dentary).

And Brian, as far as Potamotherium goes - M. Churchill just emailed me a pdf of Finarelli (2008?9?) in J.Mam.Ev. I've seen it before, but not in a long while; Potamotherium there is the sister taxon to Lutra, for cryin out loud. Granted, as Morgan stated, the purpose of the study wasn't to test pinniped interrelationships. However, I remain curious, and I think it is a very interesting hypothesis to say the least.

Bobby

Morgan said...

Fingers crossed, but a chapter of my diss will hopefully be a total evidence phylogeny for pinnipeds, including select arctoid taxa. We will see what comes of that.