An Eocene pinniped? A critique of Diedrich (2011)

Several months ago I was kindly asked by Dr. Cajus Diedrich to remove this post. I have edited certain parts for content. Following the mantra that "extraordinary claims require extraordinary evidence", I've decided to leave the post up to inform those interested in fossil pinnipeds with a series of critical comments and observations regarding the "Eocene" seal. -R.W. Boessenecker, 11/28/2012

While I was in Montana enjoying my first christmas vacation with my in-laws, I got an email with an attached pdf of a new paper that had just been published. I had expected quite a bit of time to get some work done -after all, my wife and I were up there for a week and a half and her parents would be at work much of that time - and the weather was too poor to go and do anything outside. I had already expected to get some reading and writing done, so I was pleased to hear of the new publication. Once I saw the title page, though, I was immediately skeptical, and indeed - my skepticism did not go away once I was finished with the article. The title of the article was "The world’s oldest fossil seal record", and the abstract indicated that an Eocene seal - not just any pinniped, but a phocid seal - had been discovered in Germany. I was not familiar with the author, Cajus Diedrich, whose previous work has focused on other groups (Pleistocene carnivores, Triassic marine reptiles) - but I did remember reading an article by him revising placodont (you remember, those funky sauropterygian marine reptiles with big crushing teeth) paleoecology, suggesting that most placodonts were Triassic analogs of sea cows.

The skeleton of the dawn seal, Enaliarctos - the oldest known
bona fide pinniped. From Berta et al. (1989).

Before I go any further, I should summarize why exactly one should be skeptical of an Eocene pinniped. For starters, the majority (either by taxa or number of specimens, ~99%) of fossil pinnipeds are from the Miocene or younger strata. There are a handful of bona fide pinnipeds from the late Oligocene, though, which are represented by skulls. These include Enaliarctos tedfordi from the Yaquina Formation of Oregon (~28-25 Ma), and Enaliarctos barnesi from the uppermost Yaquina Formation or lowermost Nye Mudstone (~26-23 Ma, also Oregon). There are a bunch of other species of Enaliarctos known from the early Miocene and roughly 20-25 Ma in age, including Enaliarctos emlongi from near the Nye Mudstone-Astoria Formation contact in Oregon, Enaliarctos mitchelli (early Miocene Jewett Sand of California and Nye Mudstone of Oregon), and Enaliarctos mealsi from the Jewett Sand. Slightly younger fossil assemblages from the Astoria Formation, further upsection in the Newport Basin of Lincoln County, Oregon, show a mix of "enaliarctine" pinnipeds (Pteronarctos, Pacificotaria), two species of Desmatophoca, an early 'allodesmine', and the dawn walrus Proneotherium (Barnes, 1989; 1990; 1992; Barnes and Hirota, 1995; Kohno et al., 1995). Note that during the early Miocene in the North Pacific, yes - pinnipeds first start to diversify and different groups (e.g. non-"enaliarctines"), but most of these are either "enaliarctines", members of a wholly extinct clade (Desmatophocidae), or extremely archaic and "enaliarctine"-like members of extant clades (Proneotherium).

The femur of the dawn seal, Enaliarctos. This is Enaliarctos emlongi
from Oregon. From Berta (1991).

In other words, there aren't any crown-clade pinnipeds anywhere close to the Oligo-Miocene boundary. In the North Atlantic, the oldest known pinniped with diagnostic remains is Leptophoca from the middle Miocene Calvert Formation of Maryland, crania of which were described by Koretsky (2001). In fact, this is the oldest bona-fide and widely accepted record of fossil phocids. Irina Koretsky and Al Sanders published a paper in 2002 about partial fossil femora reputedly from the late Oligocene of South Carolina (I have discussed these specimens elsewhere). To summarize - these fossils are roughly 10 Ma older than Leptophoca and were presented as being 1) the oldest fossil phocids, and 2) evidence for pinniped diphyly. For the uninitiated, there have been several morphological hypotheses for pinniped evolution, and the diphyletic view states that true seals (Phocidae) are related to mustelids/musteloids, and sea lions (Otariidae) and walruses (Odobenidae) form a monophyletic clade (Otarioidea) and share a common ursid-like ancestor, having adapted to water separately from phocids. I won't go into it now, as the Eocene seal is totally separate from diphyly/monophyly. There are several problems with Koretsky and Sanders (2002) - 1) they did not examine femora of other Oligocene terrestrial mammals, and 2) the stratigraphic provenance of those specimens are questionable (see here for more on this). To summarize: late Oligocene pinnipeds consist of only a few diagnostic fossils from the North Pacific, and modern "family" level clades do not appear until a ways into the Miocene.

The femora of the alleged Oligocene seal. From Koretsky and Sanders (2002).

Phew, now that the introduction is done, I can talk about the paper. Diedrich (2011) published a partial, proximal femur fragment (just like Koretsky and Sanders 2002), from the Fürstenau Formation of Northern Germany, which is a Lutetian age shallow marine unit deposited on the southern margin of the pre-North Sea basin, roughly 45-49 Ma in age. So, we're not even talking latest Eocene and bordering on Oligocene - this is early middle Eocene, about 5 Ma before basilosaurids show up, just before protocetids evolve. The fossil itself is phosphatized and exhibits several borings, is missing the distal end, and has clearly been reworked (for the uninitiated: phosphatization can only occur on bones or sediment below the sediment-water interface, so a bone that is both phosphatized and abraded or polished by default has been reworked). It does look remarkably phocid-like: it lacks a fovea capitis for the teres ligament - a little pit on the femoral head. It also appears to genuinely lack a lesser trochanter (as opposted to being abraded or broken off) and is very anteroposteriorly flattened. All of these features are phocid or pinniped characteristics; the lack of a fovea capitis is a probable pinniped synapomorphy (Berta and Wyss, 1994). A lesser trochanter is absent in all modern and fossil phocids and the modern walrus, but present in all fossil walruses and modern and fossil otariids. Interestingly, these are all the same features listed by Koretsky and Sanders (2002) to identify their femora from the Oligocene of South Carolina. I'm not sure that erecting the name Praephoca bellunensis for this fragment of an element with dubious diagnostic utility was prudent.

The holotype femoral fragment of Praephoca bellunensis, the alleged
Eocene seal. From Diedrich (2011).

So far so good. When oddball fossils like this crop up - ones that just smell fishy - the best thing to do is to see if something could have gotten seriously screwed up between it leaving the ground and entering the annals of a journal. Reading the Materials and Methods, it goes through a long description of the large excavation conducted at Dalum, Germany, where the Fürstenau Formation is exposed. Buried toward the end of the Materials and Methods section, I found this:

"The femur illustrated in Figure 2 was actually found was actually found in these gravels during the 1980s, and has prompted a major program seeking to understand the biodiversity of marine vertebrates in Europe during the Eocene, in relation to that of the terrestrial vertebrates. This femur, together with all material from the 2011 excavations, is housed in the Shark Center at Bippen (SCB) in northwest Ger-many, a public visitor center and museum in the UNESCO- supported “Geo and Naturpark TERRA. Vita”."

So, it sounds like this started with the discovery of the fossil femur 25-30 years ago, and then the excavation was undertaken in May 2011. Who collected the fossil originally? I just don't know. Whoever it was - especially if was an amateur collector unfamiliar with local stratigraphy - do we know that they were able to positively remember the exact locality and horizon at which the fossil was collected? 25-30 years is a long time - and people often have unreliable memories, which is why most scientists can't afford to not write important things down. I have also met collectors who have admitted to intentionally making misleading statements to researchers about the locality and provenance of certain specimens, and I've met collectors who can't remember what they collected last week. To be clear, I know many collectors who know local stratigraphy very well and remember the exact location, time, date, etc. of a fossil collection. The same variable quality of memory exists within paleontologists - which is why we really must write everything down. To summarize, the stratigraphic provenance is poor, and it is not clear if the fossil really came from that locality or not. Secondly: the fossil is reposited at the "Shark Center at Bippen". Look it up - the only results are the pdfs of Diedrich's articles. I'm not sure where this place is, or who runs it.

Modern pinniped femora (from right to left - walrus, California sea lion, and harbor seal), arrow showing the position of the lesser trochanter. While it is reduced and absent in the modern walrus, it is present in nearly all fossil walruses for which femora are known (e.g. Imagotaria, Gomphotaria, Valenictus, Proneotherium).

An additional bit of interesting contextual data is a paper published on the results of the May 2011 excavation (Diedrich 2012), which yielded 13,690 shark teeth (!!!!), 206 ray teeth, a handful of other marine vertebrates, and two indeterminate mammal bones. Not even a single isolated seal tooth; my own field collecting suggests that you should find a tooth for every 5 pinniped bones or so, and perhaps a pinniped bone for every 10 shark teeth (Purisima Fm. data from my still unpublished Master's Thesis). So, where are they? There should have been hundreds of phocid fossils, and there aren't even any cetacean bones (probably because it's too old for archaeocetes; only a couple of protocetid and remingtonocetid specimens are known from Europe, and it's too early for basilosaurids). Cetaceans are almost always more common than pinnipeds in any given marine assemblage. It just doesn't add up.

Cladogram with fossil-calibrated molecular divergence dates, modified from Fulton and Strobeck (2010). This study isn't perfect by any means (and warrants further discussion on this blog), but is a hell of a lot closer to the mark than what Praephoca would do to this cladogram.

Another line of evidence are molecular divergence dates for pinnipeds, and the "fissiped" carnivoran fossil record. The most recent molecular divergence dates published by Fulton and Strobeck (2010) suggest an Oligo-Miocene divergence of basal pinnipeds (this is, however, based on Enaliarctos as a fossil calibration). The pinniped + mustelid divergence is in the latest Eocene, and the caniform divergence occurs just earlier in the early-middle Eocene. The earliest true carnivorans don't even appear until the Eocene, and the earliest possible Caniformia appear about 42 Ma - about 3 Ma after this alleged seal fossil. Purported pinniped sister taxa like Amphicticeps, Amphicynodon, Pachycynodon, and Allocyon don't show up until the Oligocene; apparently more pinniped-like taxa like Kolponomos and Puijila aren't even in the picture until the earliest Miocene. Just on grounds of parsimony, given the ranges of these other taxa - this record should be considered suspect. Accepting Praephoca at face value, and putting it into a phylogeny would 1) telescope nearly all cladogenesis within the Caniformia ~30 million years earlier than previously thought, and 2) add dozens of ghost lineages for nearly every caniform clade across the entirety of the Oligocene and halfway across the Eocene, at that. Where are all the fragmentary scraps of the dozens of other crown-clade carnivorans in the early Eocene? They just don't exist, although they would be a natural consequence of having phocids in the Eocene.

On the other hand, I am glad that the study got published, because it gives us something interesting and controversial to talk about it - just as long as molecular systematists don't take it too seriously. This is a nagging worry, as I've seen in happen before (e.g. the Milinkovitch 1993 hypothesis, which I will talk about another time). In all seriousness - there are a number of problems with the work of Diedrich (2011), and should not be taken at face value. Extraordinary claims require extraordinary evidence - a busted up femur that may or may not be from a phocid seal and may or may not have been collected at the same site which later produced nearly 14,000 vertebrate fossils and not a single other pinniped element is not extraordinary evidence. 

References/further reading:

L. G. Barnes. 1989. A new enaliarctine pinniped from the Astoria Formation, Oregon, and a classification of the Otariidae (Mammalia: Carnivora). Contributions in Science 403:1-26

L. G. Barnes. 1990. A new Miocene enaliarctine pinniped of the genus Pteronarctos (Mammalia: Otariidae) from the Astoria Formation, Oregon. Contributions in Science 422:1-20

L. G. Barnes. 1992. A new genus and species of middle Miocene enaliarctine pinniped (Mammalia, Carnivora, Otariidae) from the Astoria Formation in Coastal Oregon. Contributions in Science 431:1-27

L. G. Barnes and K. Hirota. 1995. Miocene pinnipeds of the otariid subfamily Allodesminae in the North Pacific Ocean: Systematics and relationships. The Island Arc 3:329-360

Berta, A. 1991. New Enaliarctos* (Pinnipedimorpha) from the Miocene of Oregon and the role of "Enaliarctids" in Pinniped Phylogeny. Smithsonian Contributions to Paleobiology 69.

A. Berta. 1994. New specimens of the pinnipediform Pteronarctos from the Miocene of Oregon. Smithsonian Contributions to Paleobiology 78:1-30

C. Diedrich. 2011. The world's oldest fossil seal record. Natural Science 3(11):914-920.

C. Diedrich. 2012. Eocene (Lutetian) Shark-Rich Coastal Paleoenvironments of the Southern North Sea Basin in Europe: Biodiversity of the Marine Furstenau Formation Including
Early White andMegatooth Sharks. International Journal of Oceanography doi:10.1155/2012/565326

T. L. Fulton and C. Strobeck. 2010. Multiple fossil calibrations, nuclear loci and mitochondrial genomes provide new insight into biogeography and divergence timing for true seals (Phocidae, Pinnipedia). Journal of Biogeography 37:814-829

N. Kohno, L. G. Barnes, and K. Hirota. 1995. Miocene fossil pinnipeds of the genera Prototaria and Neotherium (Carnivora; Otariidae; Imagotariinae) in the North Pacific Ocean: Evolution, relationships and distribution. The Island Arc 3:285-308

I. Koretsky. 2001. Morphology and systematics of Miocene Phocinae (Mammalia: Carnivora) from Paratethys and the North Atlantic region. Geologica Hungarica Series Palaeontologica 54:1-109

Koretsky, I.A. and 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. Smithsonian Contributions to Paleobiology 93: 179-183.

Rybczynski, N., Dawson, M.R., Tedford, R.H. (2009). "A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia". Nature 458 (7241): 1021–24

R. H. Tedford, L. G. Barnes, and C. E. Ray (1994). "The early Miocene littoral ursoid carnivoran Kolponomos: Systematics and mode of life". Proceedings of the San Diego Society of Natural History 29:11-32.

X. Wang, M. C. McKenna, and D. Dashzeveg. 2005. Amphicticeps and Amphicynodon (Arctoidea, Carnivora) from Hsanda Gol Formation, Central Mongolia and phylogeny of basal arctoids with comments on zoogeography. American Museum Novitates 3483:1-57

New Zealand Eomysticetidae - first look

Starting in the late 1970's and early 1980's, Dr. R. Ewan Fordyce received a grant from National Geographic to start conducting extensive fieldwork on the South Island of New Zealand in search of Oligocene cetaceans and other marine vertebrates. Incidentally, non-cetaceans such as abundant penguins, sharks, and bony fish were collected as well. This fieldwork was not limited to the Oligocene, but also included forays into Paleocene, Eocene, and Miocene localities. Over the past 30 years, Ewan has established a massive collection with an astonishing number of beautiful cetaceans. Not only are these fossils beautiful in terms of their preservation, but many of them are extremely bizarre, and the assemblage as a whole includes squalodontid, squalodelphinid, ?dalpiazinid, kentriodontid, and waipatiid odontocetes, as well as several types of baleen whales (toothed mysticetes, Mauicetus and similar "cetotheres", eomysticetids, and others), and even late surviving archaeocetes. Some of these cetaceans have been described, including Waipatia and an eocene archaeocete (Zygorhiza sp.), and several other taxa are on their way to being described.

I first met Ewan in 2005 at the SVP meeting in Arizona, and I vividly remember watching him discuss how to excavate fossil whales with a chainsaw, of all things; I immediately thought it was too extreme of an excavation method for me, but after I saw it in action last monday in the field (ironically, at the same quarry the photographs from the 2005 presentation), I immediately decided I would bring this method back to the United States. In fact, it was quite funny after watching him rev up the chainsaw - an adrenaline-inducing activity in and of itself - and afterwards stating in a polite Kiwi accent "that should clean up quite nicely".

But I digress - prior to graduation from Montana State University last spring, I contacted Ewan about a Ph.D. project, and he suggested studying the large collection of eomysticetid baleen whales from the Kokoamu Greensand and Otekaike Limestone that he had established. I remembered his talk from the 2006 SVP meeting in Ottawa, part of which included a slideshow of beautiful new fossil eomysticetids. I was pretty shocked to have been offered such a beautiful (and large!) collection of fossils to study. The family Eomysticetidae was named by Al Sanders and Larry Barnes in 2002 to accommodate the new taxon Eomysticetus, which is the most primitive described toothless baleen whale (i.e. baleen-bearing baleen whale, if that makes any sense, as opposed to a toothed baleen whale). Previously, the most primitive toothless mysticetes were some of the "cetothere" whales described by Remington Kellogg from the Chesapeake Group on the east coast, AKA "Kelloggitheres"; these however were much younger than any toothed mysticete (such as aetiocetids), and there was an apparently substantial morphological gap between toothed mysticetes and Kelloggitheres. My job is to fill a bit more of this gap in with more eomysticetids from the southern hemisphere- and so far, none of them seem to be identifiable as Eomysticetus, and there are probably several new genera and species represented.

Ewan Fordyce also took on another student recently, which was a total surprise for me. Even when I first got here, it sound like it would be several months away; instead, the new student arrived only two weeks after I did, and even stayed in the same temporary apartment my wife and I stayed in the first week we were here. Cheng-Hsiu Tsai, who goes by just 'Tsai', will be studying the other big group of fossil mysticetes from the Oligocene of New Zealand: Mauicetus and Mauicetus-like mysticetes, which may be the earliest Kelloggitheres. Tsai can be seen inspecting the ventral side of one of the eomysticetid skulls in the above photo.

This specimen, for example, is one of my dissertation specimens: a new taxon, with an extremely narrow rostrum, elongate dentaries, enormous temporal fossae with a long intertemporal region, and really weird squamosals.

Yours truly, examining the extraordinarily freaky squamosals of the specimen.

Tsai, demonstrating the proper way to photograph a mysticete skull.

Yours truly, demonstrating how to use yourself as a scale bar. I am 5'8" tall.

The beautiful skull in oblique view.

Tsai examining the skull. The brass seam on the floor is actually a joint where the floor opens for a small elevator used to bring large fossils up from the basement. On thursday, I spent most of the afternoon lifting a really really heavy plaster jacket a total of about eight feet - this ordeal took about an hour and a half, three other students, Ewan, and our preparator, Sophie. Fortunately, when the jacket is prepared, it will hopefully be a lot lighter when it goes back downstairs.

Visit to the Otago Museum

I know there are some readers of this blog who have patiently waited and waited for pictures of beautiful Oligocene marine mammal fossils - to you I say, sorry for the delay. I'm going to try and get several blog posts written this weekend so I can post them incrementally. This one will mostly be in 'slideshow' format.

I've been fairly busy since I got here, and I've bordered on stress trying to figure out 1) where all the eomysticetid specimens are in collections, 2) which earbones belong to which skull or skeleton (just taking a while to become familiarized with the specimen numbers), 3) trying to make some sense out of the earbones and trying to group them based on consistently seen characteristics (and I have made a bit of headway), and 4) just generally trying to figure out how many taxa I am dealing with and thus 5) how many manuscripts/dissertation chapters this will end up making. Since I've finally made some headway and started describing the first material (a partial skull with earbones and a very partial postcranial skeleton), I've relaxed a bit and can allocate time to other activities. That being said, I'm also locked out of the building for four days due to construction/maintenance activities in the building. Fortunately, this will give me an opportunity to divert some time to my Pelagiarctos study with Morgan Churchill. Also, in other news - I finally finished up my massive manuscript describing an entire marine mammal assemblage from a locality in the Purisima Formation, which resulted in being just over 200 double spaced pages long with 45 figures; Felix Marx graciously offered to take a look, as did Ewan Fordyce. I have a bit of work left cleaning up some figures, but it should be submittable soon.

A spectacularly beautiful dalpiazinid dolphin! Look at those damn teeth! There's another specimen with even crazier incisors, and a full dentition, and jaw.

An archaic edentulous mysticete which may fall somewhere on the cetacean family tree near eomysticetids. This specimen will be part of my dissertation.

The holotype skeleton of the giant moonfish Megalampris keyesi. This set of slabs is seriously about 15 feet long and about 8 feet wide. Described by Gottfried et al. 2006.

A disarticulated skeleton of a squalodelphinid dolphin. My labmate and office mate Yoshi Tanaka is studying squalodelphinids for his dissertation (although their skulls are in better shape than in this specimen).

A partial skeleton of the giant shark Carcharocles angustidens, described by Gottfried and Fordyce (2001). Believe it or not, this specimen was found above the dolphin and moonfish skeletons in the same quarry; the shark was found first, and underneath they ran into dolphin bones; below that, they started seeing fish bones (from what turned out to be a truly monstrous fish). They called the shark Carcharodon angustidens instead, as Mike Gottfried is in the Carcharodon camp; that's fine, we all get along pretty well. Mike will be visiting University of Otago for paleo research in May, which will be a great opportunity to catch up.

Detail of the big, beautiful teeth of Carcharocles angustidens.

Beautiful jaw fragment of the undescribed squalodelphinid from the block photographed above.

The skull of the "Shag Point Plesiosaur", now known as Kaiwhekea. That's pronounced "Ky-feh-key-uh"; one Maori pronunciation is "wh" as an 'f'.

The holotype skeleton of Kaiwhekea; yes folks, that's all one gigantic concretion that is ~20 feet long. It took a crew of 3-6 to collect those blocks over the course of a month (each day).

More photos will be coming soon!

Is Puijila a pinniped?

Back in February 2009, Natalia Rybczynski and colleagues surprised the paleomammalogy community with their Nature paper naming a new genus and species of early pinniped, Puijila darwini. The holotype skeleton is relatively complete, and include fore- and hind-limbs along with much of the vertebral column, both jaws, and a well preserved skull. Puijila was about one meter long, and would have appeared relatively similar to a modern river otter. It had a short snout and a wide head, with large eyes and relatively high-crowned teeth. The teeth of Puijila still retain many of the cusps lost in modern pinnipeds, and also exhibit pits in the roof of the mouth for the lower teeth (embrasure pits). Unlike modern pinnipeds, it had a long tail, and did not have its fore- and hindlimbs modified into flippers. Puijila was discovered in 2007 from the Haughton Formation on Devon Island in Nunavut (formerly Northwest Territories in Canada). The Haughton Formation was deposited in an impact crater – the impact has been dated to 24-21 Ma (earliest Miocene), and fossil mammals from the Haughton Formation corroborate an early Miocene age. The Haughton Formation was deposited in an ancient lake that filled in the impact crater. In fact – if it were not for the impact, there would be no sedimentary rocks of Miocene age preserved that far North – all the young rocks have been eroded away by glaciation.

The skull and jaw of Puijila darwini, from Rybczynski et al. (2009).

The holotype skeleton of Puijila darwini (from http://nature.ca)

Previously, the earliest diverging pinniped (and arguably more derived than Puijila) is Enaliarctos, a fur seal sized pinniped from the latest Oligocene and early Miocene of California and Oregon. Enaliarctos retains carnassials, although many of the other dental features are very simplified and reduced, trending toward the condition in modern pinnipeds. Enaliarctos also exhibits limbs developed into flippers – and is very clearly a pinniped. But the relationships of Puijila – to pinnipeds and other carnivores – are not so clear. Because of the older age of Enaliarctos and its marine occurrence, Puijila is hypothesized to represent a lineage of early pinnipeds that stayed in their freshwater niche while marine pinnipeds like Enaliarctos evolved, remaining otterlike. It suggests that pinnipeds went through an otterlike freshwater stage before invading the ocean. Prior to this, Enaliarctos suggested a direct to saltwater invasion – although due to the absence of intermediates, it was not exactly clear one way or the other.

The skeleton and life restoration of Enaliarctos mealsi, from Berta et al. (1989).

Before we continue – I must also be specific about some clade names. Although Rybczynski et al. (2009) refer to Puijila as a member of the Pinnipedia – which is not really the traditional cladistic nomenclature for basal pinnipeds. Annalisa Berta and colleagues (1989) proposed the clade Pinnipedimorpha, for Enaliarctos and all later diverging pinnipeds. Berta (1994) later proposed the name Pinnipediformes for Pteronarctos and all later diverging pinnipeds. Pinnipedia is nested within Pinnipediformes, and Pinnipediformes within the Pinnipedimorpha. Within this traditionally accepted and utilized framework, Puijila’s obviously more primitive morphology than Enaliarctos indicates it should be referred to as a pinnipedimorph.

Rybczynski et al. (2009) listed six characteristics that unite Puijila with Enaliarctos and other pinnipeds. These are: a posteriorly expanded palate (the palate extends posteriorly past the upper toothrow in pinnipeds), an enlarged infraorbital foramen (occurring within pinnipeds due to larger whiskers and greater innervation of the snout), a shelf-like protocone on the upper fourth premolar (occurring in basal pinnipeds and some related arctoids), an upper second molar that is reduced and positioned medially to the upper first molar (reduction of the molariform teeth to conical teeth is a major dental transition within the pinnipedimorpha), a posterodorsally expanded scapula (a feature of pinnipeds, which often have very broad scapulae, an adaptation for swimming), and an expanded deltopectoral crest of the humerus (another feature in pinnipeds related to swimming).

Some of these features may be of only limited use in hypothesizing a close relationship between Puijila and pinnipeds. First, an enlarged infraorbital foramen (the small hole below the eye socket in a skull) also occurs in many mustelids, such as badgers (Taxidea), weasels (Mustela), and most (if not all) otters (e.g. Lontra, Enhydra); in badgers and weasels, this is due to a more innervated and sensitive snout, an adaptation for digging in burrows. This characteristic may not be useful in identifying early pinniped relatives, as otters (another hypothesized pinniped sister taxon) exhibit this feature – presumably evolving for the same purpose. The two postcranial features – an enlarged deltopectoral crest and a posterodorsally expanded scapula – may not be coded correctly in Puijila. To be quite honest, based on the available photographs – these features do not appear too different between Puijila and a river otter (Lontra), and don’t really exhibit the derived condition, which is much more extremely developed in Enaliarctos and other fossil and modern pinnipeds). This leaves only three reliable characters behind.

Skeletons of Enaliarctos (A), Puijila (C), and Lontra (D).

One of these features – a posteriorly expanded hard palate – also appears in the aberrant arctoid Kolponomos, as well as Pachycynodon and Allocyon (Tedford et al., 1994). This feature appears to be more widely distributed than previously admitted, although it is worth mentioning that it is probably an adaptation towards aquatic feeding. The two dental characteristics are probably more reliable, although it is odd to note that these two dental characteristics are also found in Kolponomos. Kolponomos will feature more in part two of this post, as it is both a fascinating creature which I have not yet properly covered on this blog, and it is also extremely topical to the subject of Puijila.

A wonderful reconstruction of Kolponomos by Ken Kirkland, published in Neptune's Ark by David Rains Wallance.

There are a whole host of pinniped characteristics that Puijila does not have, or features that were not described in enough detail to independently evaluate. Cranial and dental features that characterize pinnipeds (either at the level of the Pinnipedimorpha, Pinnipediformes, or Pinnipedia) include a reduced upper first molar, reduced cingulum on the upper first molar, an absent or reduced metaconid, loss of the embrasure pit between the upper fourth premolar and first molar, closely spaced mastoid and paroccipital processes, a reduced nasolabialis fossa, reduced cingulum on the upper third incisor, and a reduced trigonid cusp on the lower molars. None of these derived conditions appear to be present in Puijila. A number of postcranial features which characterize pinnipeds (either at the level of the Pinnipedimorpha, Pinnipediformes, or Pinnipedia, as above) include a short and robust humerus, enlarged tuberosities of the humerus, a flattened radius and ulna that are longer than the humerus, emphasis of certain digits in the hand and foot (i.e. largest digit in the hand being the first or “thumb”, and the lateral and medialmost digits of the foot being largest and the smallest being the middle digit), a short, flattened femur with an enlarged greater trochanter and medially inclined condyles, a reduced tail, and a short ilium (bone in the pelvis). Curiously, none of these features are present in Puijila – although nearly all of them (perhaps all – I can’t remember off the top of my head) occur in Enaliarctos.

In summary, there are very few features that actually unite Puijila and pinnipeds. The cladistic analysis of Rybczynski et al. (2009) was relatively limited, both in terms of the number of fossil and modern species used, and also with regard to the number of morphological characters used in the analysis. An earlier study – considered to be the landmark phylogenetic analysis of pinnipeds, Berta and Wyss (1994) – utilized 143 characters, while Rybczynski et al. (2009) only used 42. Granted, the earlier study focused on relationships within pinnipeds – and many of those characters may or may not apply to Puijila and other similar arctoids.

Because of the above, I am skeptical that Puijila has a close relationship with pinnipeds – and although I’m not convinced, I am equally receptive to the idea pending further analyses. There is much we’ve been waiting for – a detailed description of its anatomy and large, detailed figures of its skeleton were not included in the original study, which is understandable given the short length of Nature papers (however, it was not included as supplementary info either). There is certainly more work to be done, and there are rumors of a more detailed phylogenetic analysis in the works; such a study should include a comprehensive description of the skull and skeleton of Puijila accompanied by exhaustive figures (formerly difficult, but several modern journals have made this a far less difficult prospect), sample a broader variety of caniform carnivorans as well as more fossil and modern pinnipeds (fossil pinnipeds with postcranial skeletons such as Allodesmus, Thalassoleon, Leptophoca, Acrophoca, Piscophoca, Imagotaria, Neotherium, and Proneotherium) as well as the “beach bear” Kolponomos (which was not included in the original analysis or discussed by Rybczynski et al. 2009). Puijila certainly could belong to some group of otterlike “protopinnipeds” as hypothesized, but given the few characters uniting them, it very well could be some sort of mustelid or other aquatic carnivore.

Further reading

Official Puijila website (Canadian Museum of Nature)

Puijila, a very basal 'pinnipedimorph' (this blog)

Commentary by Ed Yong (Not exactly Rocket Science)

Commentary by Brian Switek (Laelaps)

Literature cited

Berta, A., C.E. Ray and A.R. Wyss. 1989. Skeleton of the oldest known pinniped, Enaliarctos mealsi. Science 244:60-62

Berta, A. 1991. New Enaliarctos* (Pinnipedimorpha) from the Miocene of Oregon and the role of "Enaliarctids" in Pinniped Phylogeny. Smithsonian Contributions to Paleobiology 69.

A. Berta. 1994. New specimens of the pinnipediform Pteronarctos from the Miocene of Oregon. Smithsonian Contributions to Paleobiology 78:1-30

Rybczynski, N., Dawson, M.R., Tedford, R.H. (2009). "A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia". Nature 458 (7241): 1021–24

R. H. Tedford, L. G. Barnes, and C. E. Ray (1994). "The early Miocene littoral ursoid carnivoran Kolponomos: Systematics and mode of life". Proceedings of the San Diego Society of Natural History 29:11-32.

Nobody likes Aetiocetus =(

I randomly came across this while trying to look up information for a summary about Aetiocetus weltoni I'm writing for a webpage (more info on the new webpage soon!).


Anyway, I became the first person to officially 'like' Aetiocetus. Please think of the toothed mysticetes; the Aetiocetus weltoni holotype specimen is alone this Valentine's Day. Please show Aetiocetus some love.

Pinniped ancestry: the "Oligocene Seal" from South Carolina

One of the most fascinating aspects of the study of marine mammals are the origins of the land to sea transition in various groups. Often marine mammals are so adapted for marine existence, that it is difficult to identify what group (fossil or modern) they descended from. Such has been the case with the origin of whales, for example. While I'm certainly interested in cetaceans, there has been a ton written about them, and I'm currently more intrigued by pinnipeds.

While modern cetaceans don't necessarily look like their artiodactyl relatives, pinnipeds generally retain enough features that allows them to be readily identified as carnivoran mammals, straight down to the dog-like bark of California sea lions. Certainly, this should make identifying the terrestrial progenitors of pinnipeds an easier task. Or does it?

The prevailing opinion throughout much of the 20th century was that the Pinnipedia are diphyletic; the sea lions and walruses formed the "Otarioidea", who descended from the Ursidae, and the true seals (the Phocidae) descended from mustelid (or musteloid) ancestors. In 1973, Ed Mitchell and Richard Tedford described Enaliarctos mealsi from the Early Miocene Pyramid Hill member of the Jewett Sand in Kern County, California. Enaliarctos still bore an ursid-like shearing dentition, which is absent in all modern pinnipeds (which have generally homodont postcanine teeth). Enaliarctos was purported to be the common ancestor of the Otarioidea.

Later work (which at some point will be detailed on here) by Andre Wyss (UC Santa Barbara) and Annalisa Berta (San Diego State University), proposed a drastically different phylogeny of the pinnipeds, which suggested that pinnipeds were instead monophyletic, and that walruses (Odobenidae) were more closely related to the true seals (Phocidae), forming a new group, the Phocomorpha. Dozens of molecular phlyogenetic analyses have unequivocally supported pinniped monophyly, chucking the old diphyletic view out the window. The major tenets of the new studies are the following: 1) all pinnipeds descended from a common ancestor; 2) Enaliarctos is basal to the Otariidae, Odobenidae, and Phocoidea; 3) the Otarioidea is paraphyletic, as odobenids and desmatophocids are more closely related to the phocids; and 4) pinnipeds were derived from an ursid (bear) like ancestor sometime during the Late Oligocene, probably in the Northeast Pacific, where the oldest pinniped fossils are known.

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

In 2002, Irina Koretsky and Al Sanders reported on some partial femora from the Late Oligocene of South Carolina. According to Koretsky and Sanders, these femora are most similar to those of extant phocids, and list several features they share in common. However, they argued that the Late Oligocene age of these, as well as the occurrence of these in deposits of the Atlantic Coastal Plain, indicate that true seals were already present in the Atlantic Ocean when the very primitive Enaliarctos was just appearing in the Pacific Ocean. Thus, the monophyletic origin of pinnipeds was not supported by this fossil, and it appeared that true seals evolved in the Atlantic separately from the Otarioidea, which are (during the Oligocene and the Miocene) restricted to the North Pacific.

There are, of course, some issues with this study and its inherent implications, irrespective of the incomplete nature of the fossils. For starters, the fossil record is notoriously crappy; in fact, the Early Oligocene marine record is the poorest of all with regards to marine mammal fossils. Very few cetaceans are known from the Early Oligocene worldwide, for example, primarily due to the scarcity of marine rocks for this time, due to low sea levels caused by the Eocene-Oligocene climate crash. Pinniped fossils just "show up" after sea levels rise and deposit more marine sediments during the late Oligocene, in both the Pacific (Enaliarctos) and Atlantic (Phocid femora). So - it is entirely possible for even more primitive pinnipeds to be found in earlier sediments (or, as "lazarus taxa" in Late Oligocene rocks).

The completeness of these fossils requires additional scrutiny. Some of Koretsky's other work focuses on the major elements of the fore- and hind-limb of true seals (and lower jaws) but generally placing low importance on cranial material (Koretsky and Ray, 2008). Koretsky and Sanders (2002), however, did not compare these specimens with femora of Enaliarctos, or basal odobenids such as Proneotherium and Neotherium (or an unnamed basal odobenid described by Naoki Kohno early on, ~1990). Additionally, now that the putative stem-pinniped Puijila darwini has been described, it's femora should be compared with these specimens as well. These could very well turn out to belong to something more like Enaliarctos or Puijila that we don't yet have a record of in the Atlantic. However these fossils are interpreted, their Late Oligocene occurrence (if the provenance is accurate) is intriguing, and further field investigation of Late Oligocene sedimentary rocks of the Atlantic Coastal Plain (and elsewhere!) should be considered.

References:

Koretsky, I.A. and 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. Smithsonian Contributions to Paleobiology 93: 179-183.

Koretsky, I.A., and Ray, C.E. 2008. Phocidae of the Pliocene of Eastern USA. In: C.E. Ray, D. Bohaska, I.A. Koretsky, L.W. Ward, and L.G. Barnes (eds.), Geology and Paleontology of the Lee Creek Mine, North Carolina, IV. Virginia Museum of Natural History Special Publication 14: 81-140.

Benthic feeding in basal mysticetes, part 2: Mammalodon, the freak

Sorry about the "short" delay; the last week or so has been pretty rough, between my Paleobiology course, getting sick, and administering/grading my first exam. But, all of that's over now, so I've been able to allot some time to this again.

My last post concerned paleopathology and histology of the "cetothere" Diorocetus hiatus, published by Brian Beatty and Alton Dooley last summer in Jeffersoniana. In it they posited that Diorocetus may have been a benthic feeder based on peculiar pathologies as well as an interesting pattern of rib osteosclerosis.

Comparison of the size of Mammalodon and a blue whale. From http://museumvictoria.com.au

There's been some buzz in the science blogosphere recently about the truly bizarre Australian toothed mysticete Mammalodon, the subject of a new monograph by colleague Erich Fitzgerald. I'll admit I've been anticipating this paper since Erich's talk at SVP in 2008 (the same session as my first ever SVP talk, you know, the one where no one could see any of my text). Some other blogs have covered Mammalodon already, but mostly just some of the stuff you already hear in the news; ya, it was a mysticete with teeth (all toothed mysticetes look pretty weird), and it likely a benthic suction feeder, so what? There's far more interesting 'meat' in the paper, if you will, that someone who wasn't a mysticete worker and therefore didn't have time or interest to read 110 pages might not pick up on. Okay, I didn't read the description, but I've read the in depth discussion.

The skull and dentary of Mammalodon. From http://museumvictoria.com.au

Mammalodon colliveri was originally described in 1939 from the Oligocene Jan Juc Formation of Australia, although it was not identified as a toothed mysticete until the 1980's when Ewan Fordyce (U. Otago, New Zealand) undertook additional preparation of the fossil. In 1966, Doug Emlong (an extremely prolific and gifted amateur collector) described a peculiar toothed cetacean he discovered in the Oligocene of Oregon: Aetiocetus cotylalveus. Emlong thought it was an archaeocete, but Leigh Van Valen soon after recognized several mysticete features. Toothed mysticetes may seem odd at first, but when you think about it - 1) teeth are primitive for cetaceans and indeed mammals, and 2) they had to eat with something before baleen evolved. Mammalodon shares many similarities with Janjucetus, including a short rostrum, short triangular supraoccipital, and large orbits; however, Mammalodon is distinct in having laterally oriented teeth, and a relatively flat rostrum.

Comparison of Mammalodon (left) and Janjucetus (right). From Fitzgerald (2010).

Mammalodon has some strange features - a short, flat snout, large, upward facing orbits, large foramina on the maxilla, upper teeth that project laterally, and peculiar wear facets on the lower dentition that look like they were filed down at the same time (so to speak) - i.e. they share wear facets oriented on one single plane. Some authors have interpreted the denticulate teeth of basal mysticetes like Llanocetus and Mammalodon to have had a role in filter feeding, much like the teeth of the extant crabeater seal (Lobodon carcinophagus). Fitzgerald (2010) rejected this interpretation, as he did earlier (2006) for the tooth morphology of Janjucetus. Based on the probable presence of hyaline cartilage in the jaw joint of Mammalodon (as opposed to fibrocartilage in lunge feeding balaenopterids), Fitzgerald also rules out lunge filter feeding. Bony correlates of baleen, nutrient foramina, are absent on the palate of Mammalodon, suggesting that it did not possess baleen (such as later diverging aetiocetids - I'll talk more about those next time). Taken in full, few features of Mammalodon suggest filter feeding, rather than raptorial/pierce feeding (aka, biting stuff). Aside from this, some of the features unique to Mammalodon such as the very short rostrum, large maxillary and mandibular foramina, and extreme tooth wear suggest an alternative behavior. Typically, large foramina indicate improved blood flow and innervation to a region; for example the tactile whiskers of pinnipeds are correlated with a greatly enlarged infraorbital foramen (a pinniped synapomorphy), relative to "fissipeds". In this case, the short rostrum, probable highly innervated oral region, and wear most likely due to substrate interaction, all point towards benthic suction feeding. Additionally, the up-and-forward facing orbits would have conferred some degree of binocular vision, similar to the walrus and the bizarrer walrus convergent odontocete, Odobenocetops.

Various archaeocetes (top row), mammalodontids (second row) and aetiocetids (bottom two rows). From Fitzgerald (2010).

Most interestingly are the implications of the phylogenetic hypothesis of this study on the evolution of feeding in the mysticetes, relative to other recent hypotheses. Raptorial feeding is primitive for cetacea as a whole, including basal mysticetes. Interestingly, Llanocetus, Janjucetus, and Mammalodon all form a southern toothed mysticete clade, and Fitzgerald (2010) lumped Janjucetus and Mammalodon into the family Mammalodontidae, scrapping the family Janjucetidae he proposed earlier (2006). Llanocetus exhibits no adaptations for suction feeding, although Janjucetus does, suggesting that suction feeding is derived for this clade, but not a typical feature of basal mysticetes in general. Thus, this suggests that whatever feeding mode the mammalodontids employed was likely not representative of early mysticetes, contra Fitzgerald (2006).

Feeding evolution in baleen whales. From Fitzgerald (2010).

What the hell is Llanocetus, anyway? Llanocetus is perhaps the most interesting and strange described/undescribed cetacean out there. Well, what does that mean? Llanocetus was collected from the late Eocene La Meseta Formation of Antarctica. Yes, the Eocene of Antarctica, my friends. Why is that particularly awesome? The Eocene is dominated by archaeocetes, and elsewhere on earth during the late Eocene fantastic critters like Basilosaurus and Dorudon were kicking ass and taking names. And Llanocetus is the earliest known mysticete, let alone record of the Neoceti. The original description of Llanocetus denticrenatus by Ed Mitchell (1989) includes a maxillary fragment, mandible fragment, and an endocast - overall, marginally crappy. Later on, Ewan Fordyce revisted the site and collected what he initially thought was an archaeocete, and it even included (apparently) vestigial hindlimb elements (plural), similar to the condition in basilosaurid archaeocetes (which are not too phylogenetically divorced from Llanocetus, after all). This turned out not only to be a toothed mysticete, but the remainder of the holotype skeleton. My guess is that whoever originally collected the holotype scraps was freezing their ass off and said "to hell with it" and left. However, even though a cast of the skull is now on display at the USNM, the rest of the holotype is not yet described, and the dotted outline provided by Fitzgerald (2010) is the most informative figure ever published of this rather interesting beast. Anyway, I'll be pretty excited whenever the description gets published (much of the above information was presented by Fitzgerald, 2010, in his discussion of taxa used for the cladistic analysis).

The next post will (hopefully) be less-rambling, and will detail the transition from teeth to baleen in archaic mysticetes.

References:

Fitzgerald, E.M.G. 2006. A bizarre new toothed mysticete (Cetacea) from Australia and the early evolution of baleen whales. Proceedings of the Royal Society B: Biological Sciences
273: 2955–2963.

Fitzgerald, E.M.G. 2010. The morphology and systematics of Mammalodon colliveri (Cetacea:Mysticeti), a toothed mysticete from the Oligocene of Australia. Zoological Journal of the Linnean Society. 110p.