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.