Monday, July 21, 2014

Eodelphis kabatensis illustration on the cover of JVP

Last year I was contacted by my friend and colleague Mizuki Murakami (now Dr. Murakami), who wanted to commission an illustration of a fossil odontocete from Japan for a manuscript he was working on and planning on submitting to the Journal of Vertebrate Paleontology in the hopes that it would be accepted and selected as the feature article. To make a long story short, it was. The illustration depicts "Eodelphis" kabatensis - a fossil delphinid and possible ancestral globicephaline or orcinine (think "blackfish" in general) that was originally named in the late 1970's by Hideo Horikawa from the late Miocene of Japan. Horikawa originally named it as Stenella kabatensis, recognizing its delphinid affinities - but subsequent workers have noted it doesn't belong in the genus Stenella, referring to it with scare quotes as "Stenella" kabatensis. Mizuki's new study redescribes this fossil (consisting of a well preserved braincase, periotic, tympanic bulla, partial mandible, and hyoid) and gives it a new genus name: Eodelphis. Unfortunately as it turns out - Eodelphis is a preoccupied name for Cretaceous marsupial. So, it will require an additional paper proposing yet another replacement name.


The cover of JVP with my illustration of "Eodelphis" kabatensis.

Eodelphis was found by Murakami et al. to be the earliest diverging member of the Orcininae, a tenuously supported group also including the modern killer whale Orcinus (and the fossil Orcinus citoniensis), the miniature killer whale-like dolphin Arimidelphis, and the robust bottlenose-like dolphin Hemisyntrachelus. Further work is needed to tell if this clade is genuine; other analyses of molecular data have been pretty variable in the placement of Orcinus. To reflect these relationships and the fact that Eodelphis would have probably been somewhat more generalized, Mizuki requested a dolphin with a body shape similar to the more "primitive" living globicephalines like the pygmy killer whale (Feresa attenuata), Risso's dolphin (Grampus griseus) and the melon headed whale (Peponocephala electra). The end result was essentially a mix of sorts of these three species - a plausible "look" for an ancestral large bodied delphinid (whether orcinine or globicephaline).


I was pretty damned happy to see a physical copy once it arrived here in Dunedin. I think this is my labmate Cheng-Hsiu Tsai's copy. I've had art show up in press releases before, but this is the first time my artwork has made it onto the cover of a journal.


And, here's the original illustration.

Thursday, June 26, 2014

More discoveries from the Naseby Greensand - sharks, amber, and giant penguins

Last week, Marcus came in from four days of fieldwork in the Naseby Greensand, and started lugging in box after box and bag after bag of fossils and sediment. He seemed pretty excited - unusually excited considering he had just returned (normally I'd be a bit tired and would need some recovery time at home), and he proclaimed that he had collected a bunch more shark teeth and a penguin skeleton.


After a couple of hours, Marcus had laid most of his finds on a number of trays on the museum table. Here, Marcus, Ewan, and Tsai examine Naseby specimens at tea time.


Preparator Sophie White and visiting student Ehecatl Hernandez-Cisneros (Universidad Autonoma de Baja California Sur) examining unprepared blocks of penguin-bearing rock. Labmate Yoshi Tanaka is on the left.


Some of Marcus' shark and fish teeth - an odontaspid sand tiger (big tooth with cusplets) and a possible cutlass fish, Trichiurus (large black triangular tooth). This photo is horribly out of focus, but I did not want to ask Marcus to take out all of his specimens again just for a marginally better photo.


Marcus also brought back some rather large chunks of amber - on the previous visit I found a smallish piece about the size of a large corn kernel (my first piece of amber ever!); this one was about the size of a donut hole. Amber, for the uninitiated, is fossilized tree sap/resin.


Chunks o' penguin - at least two humeri, a partial tibiotarsus, an ulna, pedal phalanges, and a half dozen vertebrae or so are represented.


Here's the proximal end of the left humerus - as you can see, this is a pretty damn big bird. This humerus is pretty incomplete...


...but the other humerus is virtually complete. The right humerus is in several pieces, but can be easily glued back together once dried. Provisionally speaking, this humerus is similar in size and morphology to the recently described giant penguin Kairuku, but obviously preparation is necessary to tell for sure.


Marcus and Ewan discussing the weekend's bounty, and Sophie determining the best course of preparation for the material. Marcus is thinking seriously about continuing this project into a Master's project and describing the vertebrate assemblage; he's got his work cut out for him! It reminds me quite a bit of my first research project - going to a virtually unstudied exposure of the Purisima Formation in California, collecting every vertebrate fossil, and publishing (nearly) every specimen. The best part is that Marcus was still unsatisfied with this rather large haul, and went out last weekend and brought back even more shark teeth, and found a phosphatic tooth-rich bonebed horizon that is fairly densely fossiliferous. We may be going on a field trip there next week sometime.

Wednesday, June 25, 2014

Fishing in the Oligocene: catching a big teleost in the Naseby Greensand

I haven't had much opportunity for field work in the past year or so. Our lab was fairly active during my first year and a half of studies here, but we got to the point where too many plaster jackets had accumulated in various places, and we didn't have any room to add any more. During my first year, on one single visit to a quarry in South Canterbury, in less than two hours we found a penguin skeleton, two dolphin skeletons, a fragmentary dolphin mandible, and two (or three?) very partial baleen whale skeletons. We had to return two more times to successfully excavate and jacket everything. The two dolphin skeletons have finally - in the last month - been exposed in the lab, and the less spectacular of the two has a partial skull with a more or less complete braincase, associated teeth, and postcrania; the other specimen is a virtually complete skeleton with skull, mandibles, teeth, tympanic bullae, periotic, most of the vertebral column, complete left and right forelimbs, and ribs. In comparison with much of the other material we have here, it is one of the most complete odontocetes we have - and probably one of the most (if not the most) complete fossil odontocetes from the Oligocene, anywhere. My adviser, Ewan Fordyce, recently received funding for a preparation "triage" for unopened plaster jackets; this recently collected material has all been dealt with, and now our preparators are beginning to open jackets from 2010. One enormous, ~2.5 meter long jacket with much of a baleen whale skull inside remains to be opened, but it is very promising progress on a rather large backlog of unprepared material.

So, when I got the invitation from undergraduate Marcus Richards (B.Sc. Honors) to go out to his field area in North Otago in the Kyeburn area (with the prospect of finding some Oligocene shark teeth and to help dig out a big teleost skeleton he had found) - I jumped at the opportunity. Marcus is doing a study of the stratigraphy, age, and paleontology of the Naseby Greensand - a stratigraphic unit of probable late Oligocene age that is thought to be a lateral equivalent of the Kokoamu Greensand a bit further north. The Kokoamu Greensand is generally mapped north of the Kakanui Range - an east/west oriented mountain range that meets the sea about an hour's drive north of Dunedin, near the sleepy town of Palmerston. On the south side of the Kakanui Range, similar greensand occurs but without the overlying Otekaike Limestone, and it is thought to be closer to shore; here it is mapped as the Naseby Greensand, it is considerably less well understood, probably because the outcrops are fewer, less spectacular, and generally more difficult to access than those in the Waitaki Valley region. A few weeks prior, Marcus had brought in a handful of fragments he had collected, including a couple of flat bones, a couple vertebrae, and a large dentary with well-preserved needle-like teeth. He indicated there was more left in the hillside, and that it could be quite large. The vertebrae were similar in size to modern fish approaching two meters in length - and this fish could easily be the size of a modern enormous tuna or small swordfish.

We unfortunately don't have many photos from the first day, so a quick synopsis is necessary. Marcus, postdoctoral teaching fellow Uwe Kaulfuss (a paleobotanist/paleoecologist), my wife Sarah, and I drove out to the locality, stopping three different times for coffee at Uwe's insistence (I thought I was a coffee freak). It was forecasted to be one of the last nice days before winter really set in, and it was in fact the official first day of winter in NZ. In the sun, it was about 10-12C (50-54 F for American readers back home), so not frigid, but not toasty by any means either. I generally have a difficult time in any weather over 75 F (~24C) anyway, so this was actually optimal. Marcus showed us the spot where the fossil fish was: up on a hillside, with a small cliff below. The cliff was steep enough to prevent us from walking directly uphill to it, requiring us to hike down to it from above through tussock grass, which is a bit awkward to walk through since you can't see the ground where your feet are planting - a bit alarming when you're within a few feet of a ten foot drop. We spent most of the day collecting the few bits that were exposed on the surface, digging a trench the fossil, uncovering more bones (by accident) in the trench and bagging up those, and eventually getting the fossil into a condition ready to jacket. During the excavation we bagged up another half dozen vertebrae and what looks to be a partial skull. At 4pm the sun went down, and my hands went into icy water to start mixing the plaster (by the way, if you are ever digging in a spot where you need to get water up a steep incline and don't want to risk hauling it up in a bucket that can spill - just pour the water into a large freezer ziplock bag, it works great). The water was straight out of the river below and was so unbelievably cold. As the sun went down over the hill, we felt the air temperature drop to about 0C (32F) within five minutes. Marcus, Uwe, and myself worked quickly to apply the jacket, clean up, and leave. A return to the locality would be necessary - soon - in order to remove the jacket before it just got too damn cold to do anything about it.


Four days later Marcus, Tsai, and I returned to the locality to finish the excavation. In this photo of Marcus and I you can see the vertical face just a few feet behind Marcus, which originally was an even slope until we chopped a big ledge into the hillside.


There was a pretty nice view looking north towards Dansey's Pass. And yes, that's snow. There should even be more of it this time of year. Matter of fact, the first day, the road was still closed because of a snowstorm that blocked the pass (further up the road, of course) so we had to park and walk up about two kilometers. When we returned, the road was opened again and Marcus drove to within about 100 meters of the excavation site.


Marcus eventually got fed up with having to hike way around the hill, so he carved in a handful of precarious footholds for a more direct ascent from the spot at the bottom of the hill where we kept most of our gear.


Within a half hour we had flipped the jacket over and began trimming it down. Prior to trimming, the jacket weighed well over 150 pounds or so - not enormous, but far larger than it had to be. As it turned out, the bedding here was also near vertical or perhaps around a 60 to 70 degree angle - so the bedding plane with the fossils was actually exposed on the side of the pedestal. We began "carefully" scraping rock out of the opposite side, working our way down to the ~4-6" thick zone where disarticulated fish bones were known to be present. Here Tsai and Marcus are working on the final trimming. We had to cut away about 10" of empty plaster jacket siding after removing rock from the jacket. The rock, by the way, was this wonderfully compliant lightly consolidated muddy greensand and very easy to dig through. Although the others were a bit skeptical and thought we risked damaging the bone, I insisted that we scrape it down until we get to the bone layer, leaving a 4" thick "surfboard" of rock inside a relatively light and easy to remove jacket. There is nothing worse than having a jacket that is too difficult to safely lift. Also, there was another safety concern nagging at the back of my mind...


Generally it's best to use paper towel as a separator. Without a separator, the plaster will stick directly to the rock and bone alike and become a complete pain to remove. Newspaper works fine, but occasionally ink can be transferred onto the specimen. The first day we had forgotten to bring anything for wrapping small fossils or as a separator, so Marcus had to run back to the Dansey's Pass Coach Inn and see if they could spare some toilet paper and newspaper (which they did, and we were very greatful for it). In the past decade, I've also learned that a camelback not only keeps you hydrated, but is an excellent way to get a nice coat of water onto a separator like paper towel or newsprint. If you put on the separator dry, the wind will often just blow it away; it's also easier to get it to conform to the shape of the rock pedestal if it's damp.


That's some cold river water. This time, we started jacketing at about 2pm.


Marcus and I putting the final touches onto the opposite side of the jacket.


And that about does it - after a bit of waiting, we had to figure out how to remove the jacket. That morning I inquired with various geology staff whether or not anyone had a cargo net - an odd question, but we have so much random equipment here you never know and might as well ask. Unfortunately, that was one piece of equipment nobody seemed to have. I wanted to lower the fossil down the hillside rather than haul it up and over - which would be a nightmare. The rock is soft enough that unless considerable effort went into carving steps, that much weight would just result in someone sliding. Watching a carefully made jacket with a priceless specimen inside bouncing down a hillside and bursting apart is one of my worst nightmares.


While we were unable to find a cargo net, I did find an alternative...


In the paleo equipment storage room, we've got an unusually thick burlap sack (or hessian sacks as they call them here) that's usually used as something to put the chainsaw on top of when out in the field. I figured that if we could put the jacket inside of it, we could tie ropes to it and carefully lower it down the hillside.


Fortunately, the jacket was just small enough to be slipped inside the burlap sack. Unfortunately, the burlap sack (like most) does not have brass grommets, so in order to tie ropes to the sack, I used an old trick I learned in my days in boy scouts: find a small rock from the river below, stick it into the corner at the opening, pull the burlap tight around the rock, and then tie the rope around the neck of the "pouch" that the rock is sitting in: the rock is wider than the rope knot, and cannot leave the small pouch you've made.


It worked like a charm.


I was actually surprised at how light the jacket was - it took barely any effort at all to control it as it went down the hillside.


And, the best part is, we made it into the car at around 4pm just around when the sun went behind the hill. Here's Marcus with his prized catch inside, ready for the two hour trip back to town. We're really looking forward to seeing what is inside the jacket, and for having the other fish bits that we collected during the trenching process prepared.

Next up: more of Marcus' treasures from the Naseby Greensand.

Thursday, June 12, 2014

Fossil discoveries at the Calaveras Dam in the east bay

I recently saw a news piece on KQED.com about some middle Miocene marine mammal fossils being found during the repairs and construction going on with the Calaveras Dam in the east bay (East San Francisco Bay area, that is). Few marine mammal fossils have been collected from the east side of the bay in the last 75 years thanks to extensive overgrowth and proliferation of paleontologically unmitigated construction, so I was pretty happy to hear about this.

The original article can be read here: Fossils Unearthed during Calaveras Dam work near Sunol Regional Park, by Sharol Nelson-Embry


A (lower?) tooth of Carcharocles megalodon, from www.blogs.kqed.org.

The fossils include baleen whales, desmostylian remains, and even Carcharocles megalodon teeth, above. The deposit is apparently mapped as being part of the Temblor Formation - I had no idea it was mapped as far north as the bay area, and am wondering if its not some local lateral equivalent.


East Bay Regional Park personnel share some of the finds with visitors. From www.blogs.kqed.org.



There's some sort of baleen whale in here, and the piece sticking out is identified as an ear bone. Needless to say, my curiosity is piqued!

I'll admit now that I have known about this for a while, and am pleased that they've made a series of further discoveries. The middle Miocene is well-known from Sharktooth Hill and a couple of other localities in Southern California and Oregon, but not further north. So, it will be interesting to see if the diagnostic marine mammals are the same species seen further south - or not. I even had a discussion about these fossils with someone at SVP, and I cannot now for the life of me remember who that person was. If that person is reading this right now... please email me! Normally my memory isn't this terrible, so I apologize in advance.

Otherwise, I've sent an email to the folks in charge as I'm genuinely curious to see which museum this material is heading off to eventually.

Tuesday, June 10, 2014

The best known fossil pinniped, part 4:Phylogenetic relationships and evolution of Allodesmus, and future directions

Finally, we're at the last post in this series - one that I've been procrastinating on, as I knew it would be a total bear to write. But, now I'm done! Hooray. Next up after this - a recent announcement of fossil marine vertebrate discoveries in the East Bay (e.g. east San Francisco Bay Area) and some photos from a recent field excavation, or as I like to call it, going fishing in the Oligocene.



The phylogenetic position of Allodesmus

The relationships of Allodesmus have been a serious bone of contention (pun intended…sorry) in pinniped paleontology for several decades, and is a bit of a polarizing issue within the field. I have my own biases which no doubt will shine through below, but will try to show both sides of the argument. Two major camps exist within pinniped paleontology: those in favor of pinniped diphyly and otarioid monophyly (Otariidae + Odobenidae + Desmatophocidae + enaliarctines), and those who embrace pinniped monophyly and phocoid monophyly (Phocoidea is a Desmatophocidae + Phocidae clade).


A handy hand drawn phylogenetic tree with illustrations of skulls. From Barnes et al. (1985). Although outdated, no subsequent illustration has ever been put together of this caliber for pinniped evolution, and I've always wanted to redo this given our substantially expanded fossil pinniped record.
Mitchell (1966) arguably represents the first “modern” treatment of Allodesmus, and while he did not explicitly propose any phylogenetic hypothesis for pinnipeds, he  recognized that Allodesmus was quite derived and probably not directly ancestral to living sea lions. Prior workers, in the absence of other fossils, implicated the fragmentary remains of Allodesmus in the ancestry of modern pinnipeds. We now know that desmatophocids were a relatively highly derived evolutionary experiment that lasted for about 10 Ma – and ultimately went totally extinct – and despite predating true seals (by 5 Ma), walruses (by 2-3 Ma), and fur seals and sea lions (by 10 Ma or so) – desmatophocids evolved independently from early pinnipeds and did not give rise to any of these modern groups. Given the sheer abundance of Allodesmus in the mid Miocene fossil record, it is ultimately unsurprising that it was one of the earliest discovered fossil pinnipeds; unfortunately, this also remained one of the only well known fossil pinnipeds for quite some time, and it was not until the 1970’s that paleontologists could make heads or tails of it.
Allodesmus was classified as an otariid relatively early on by such researchers as Remington Kellogg, Theodore Downs, and Victor Scheffer. Mitchell (1966) suggested some relationship with walruses and sea lions, and erected the subfamily Desmatophocinae to include it and Desmatophoca (and curiously, the walrus Dusignathus) within the Otariidae (=Otarioidea of other workers). It must be stated that during the 1960’s, 1970’s, and 1980’s, most pinniped researchers were working under the implicit assumption that pinnipeds were diphyletic – with walruses and sea lions sharing a common bear-like ancestor, and true seals evolving separately from a mustelid ancestor (more on this later).


The phylogenetic hypothesis of Barnes (1972). 
Barnes (1972) recognized that desmatophocids diversified prior to the appearance of otariids, and even recognized that otariids were more primitive than desmatophocids in many regards, despite diversifying long before the appearance of the earliest fossil otariids. Barnes (1972) was appropriately skeptical that otariid ancestry had anything to do with desmatophocids, and suggested that otariids were secondarily derived from a primitive ancestral stock, and similarly indicated that desmatophocids could probably not be implicated in walrus origins either. Barnes’ (1972) proposed phylogeny can be seen above. Mitchell (1975) published a phylogenetic hypothesis which did not differ appreciably from Barnes (1972).


The phylogenetic hypothesis of Mitchell (1975). 
A later study by Repenning and Tedford (1977) showed a more or less similar phylogeny, with desmatophocids and odobenids sharing a more recent common ancestor than otariids. Repenning and Tedford (1977) further agreed that no modern pinnipeds could have been derived from the desmatophocids.


The phylogenetic hypothesis of Repenning and Tedford (1977). 
New research published by Andre Wyss in 1987 indicated the possibility that pinnipeds were not only monophyletic (spurred by early studies of molecular phylogeny), but that walruses and true seals (together with desmatophocids) might form a monophyletic group (the clade Phocomorpha). As a response to this, Barnes, in his 1989 description of the enaliarctine Pteronarctos goedertae, published a new phylogeny for fossil and modern pinnipeds (see below). Curiously, one of the earliest comments regarding Wyss’ hypothesis of pinniped monophyly was that his “conclusion is contradictory to that reached by many other researchers who have examined many of the same characters as Wyss”. Although a fair comment here, this point has been reiterated time and again by proponents of pinniped diphyly, in print and in person to the point where it is reminiscent of an appeal to authority. But I digress. Barnes (1989) shows a hand-drawn cladogram depicting otarioid relationships, and pointed out a couple of minor holes in Wyss’ arguments, including the observation that phocids, desmatophocids, and the enaliarctine Pinnarctidion all share a “mortised” (e.g. vertically thickened/expanded) zygomatic arch (or cheekbone for the uninitiated). Barnes pointed out that some odobeninae also possess this in addition to sirenians and desmostylians, and that the convergent nature of this feature means it should be avoided in phylogenetics. Such arguments are commonplace in vertebrate paleontology, and the idea that certain types of characters ought to be avoided because they are convergent is pervasive. However, the moment any character evidence is ignored – for any reasoning – is the moment that subjectivity is introduced into the analysis. Conversations with Jonathan Geisler back in January 2011 opened my eyes to this, and as a result, my own philosophy is to include as much character evidence as possible.


The phylogenetic hypothesis of Barnes (1989). 
Regardless, Barnes (1989) did not present a computer-assisted analysis, but rather listed a series of characters supporting otarioid monophyly, and other clades within the Otarioidea. In a non-computer assisted analysis, a hand-drawn cladogram is assembled based on the listing of characters supporting “premeditated” clades – no testing is involved, and it is completely subjective. The 1980’s saw the proliferation of computer-aided cladistic analysis (referred to hereafter as just cladistic analysis). For the uninitiated, cladistic analysis emphasizes the grouping of organisms based on shared features rather than differences. This sort of analysis is conducted by producing a list of characters (e.g. characteristics or features) with different character states (e.g. conditions). An example of a classic (and already mentioned) character for fossil pinnipeds would be:

Character 1: zygomatic arch. 0-splintlike, zygomatic process tapers. 1-mortised, distal zygomatic process is dorsoventrally expanded.

This character would be coded as such:

Grizzly bear (Ursus): 0
Enaliarctos (earliest fossil pinniped): 0
Northern Fur Seal (Callorhinus): 0
California Sea Lion (Zalophus): 0
Walrus (Odobenus): 0
Desmatophoca: 1
Allodesmus: 1
Harbor Seal (Phoca): 1
           
            All species coded as ‘1’ would be grouped by the computer into a clade. In this case, the supported clade would be the clade Phocoidea. It is possible to have more than two character states; only derived character states (e.g. anything other than zero) will unite species together. When an analysis includes hundreds of characters like this, it is likely that some will be mutually exclusive: for example, in the context of this discussion, some characters might support otarioid monophyly and others might support phocoid or phocomorph monophyly. What happens when two characters support mutually exclusive groups of species? The short answer is that, as you might suspect, they cancel each other out. At larger scales, if an analysis includes dozens of characters that support mutually exclusive clades – they will also cancel each other out if they are of roughly equal proportions. This can be solved by one of two ways: ignoring characters that support a clade you don’t like, or searching for additional characters that might support one hypothesis over another. Admittedly, the first option sounds dangerously unscientfic (…because it is), but plenty of paleontologists are guilty of this practice, unfortunately.

An excellent summary figure contrasting the "newly" proposed phylogeny under the "Phocomorpha hypothesis" of Berta and Wyss (1994) with the "classical" view of pinniped diphyly advocated by most earlier researchers. From Berta and Wyss (1994).
            A response to the phylogenetic hypothesis of Barnes (1989) was a large cladistic analysis of morphological data by Berta and Wyss (1994) that still remains the only comprehensive phylogenetic analysis of pinnipeds (as alluded to below, Morgan Churchill and I presented an even larger analysis at the 2010 SVP meeting, but it needs a lot more work and was a good “first stab”; comprehensive phylogenetic analysis of pinnipeds remain a viable future research project). This study used 143 characters including skeletodental, soft tissue, and even behavioral characters. Berta and Wyss (1994) found strong support for a monophyletic Pinnipedia, monophyly of the Phocomorpha (walruses + desmatophocids + true seals), and monophyly of the Phocoidea (Desmatophocidae + true seals + Pinnarctidion). Berta and Wyss (1994) identified that the sheer majority of purported synapomorphies for the Otarioidea also occurred in terrestrial arctoids (indicating that they are primitively present in “otarioids” and are thus not phylogenetically informative), and that many other features are also present in true seals (which, of course, were not considered by Barnes because of the a priori assumption that pinnipeds are diphyletic).


The phylogenetic hypothesis of Berta and Wyss (1994); black bars denote the number of synapomorphies for each node (I think). 
            A biting response to this analysis was published less than a year later by Barnes and Hirota (1995) who criticized the definition of a few features (some of which were later acknowledged by Deméré and Berta, 2002, to be valid criticisms). Barnes and Hirota (1995) made some comments on Berta and Wyss characters which in my mind don’t make much logical sense. For example, they criticize the use of a character based on the presence of an enlarged digastric insertion on the mandible as it is “related to the musculature and functional morphology of the dentary and not of phylogenetic significance” (Barnes and Hirota, 1995:356). So what? I fail to see the distinction here: all morphological features are influenced by function to some degree, and either characteristics have a known function, or the function is unknown and we simply do not know enough to make an informed statement about the functional significance of a certain feature. The second puzzling statement is a criticism of the use of soft tissue features by Berta and Wyss (1994), as “soft anatomical structures that are not reflected by bone morphology cannot elucidate the relationships of fossil taxa”. While it is true that such soft tissue features are not preserved in desmatophocids, they are present in the walrus, which is sister to the desmatophocid + true seal clade (Phocoidea) in the analysis of Berta and Wyss (1994). Here’s the problem with this statement: when it comes to cladistic analysis, soft and hard tissue characters hold no inherent value over one another: they are all equally important according to the computer. To the computer, a soft tissue character codable only for modern pinnipeds is no different from, say, mandibular characteristics that can only be coded for fossil and modern species with preserved mandibles: no distinction is made. Thus, the argument that a certain character is irrelevant because it can only be coded for a small number of species is erroneous. To further illustrate this, there are some skeletal characteristics that could potentially be coded for fossil pinnipeds – if found beautifully articulated – that can generally only be coded in modern specimens. Subsequent studies have focused on smaller groups of pinnipeds, and not a single morphological study since has really tested any of the larger clades within pinnipeds – and that includes the phylogenetic position of Allodesmus as a true seal relative.
            So, where does that leave us today? It’s now 20 years since Berta and Wyss (1994) was published, establishing a new paradigm for pinniped phylogeny – and we are still without a followup to it. It is an excellent paper, and I strongly recommend that any student of pinniped evolution read it. However, there’s a serious catch. Virtually all published studies of molecular data have unilaterally supported an otariid-odobenid clade (Otaroidea – walruses and sea lions), and also supporting pinniped monophyly. So, molecular phylogeny suggests a bit of a compromise between the two extremes. But, molecular analyses – like soft tissue data – are inapplicable to the question of where Allodesmus fits in. The postcranial skeleton of Allodesmus is very similar to odobenids and otariids – while many features of the skull are more similar to true seals. Personally, I’ll remark upon the fact that there are far fewer skeletal features linking walruses with Phocoidea than there are supporting the Phocoidea (desmatophocids + true seals), and I could be convinced of otarioid monophyly if someone were to carefully identify a suite of synapomorphies. In this context, my own suspicion is that molecular work is probably correct – but as of yet I cannot point to much morphological evidence in support of it – and that Allodesmus most likely, given the volume of shared features identified by Berta and Wyss (994), does share common ancestry with the true seals. Much, much more work is necessary to test all of these hypotheses, and I am not particularly beholden to any idea, other than it is abundantly clear that pinniped diphyly is an outdated concept not supported by modern science and lacking molecular and anatomical support. Another post on pinniped diphyly would be instructive.

Evolution of Allodesmus

Regardless of larger phylogenetic relationships, a few comments can be said about the evolution of this fossil pinniped are worth making. Allodesmus is the sister genus of Desmatophoca – and if a genuinely separate genus, Atopotarus is closer yet to Allodesmus. Desmatophoca is fairly old – the type specimen of Desmatophoca brachycephala is perhaps as old as 21 Ma, demonstrating that desmatophocids diverged fairly early from enaliarctines. Desmatophocids in general are noteworthy for being the earliest large bodied pinnipeds to evolve; both species of Desmatophoca are large, and most species of Allodesmus are even larger. Numerous changes occurred between the evolution of Allodesmus from Desmatophoca-like morphology (fossils from the Astoria Formation purportedly show that Desmatophoca oregonensis and an “Allodesmine” co-occurred, thus demonstrating that the two do not share an ancestor-descendant relationship – but this undescribed Allodesmus/Allodesmine has yet to be described; Barnes and Hirota, 1995). Changes in the skull and mandible include elongation of the rostrum, enlargement of the orbits, development of a prenarial shelf, further elaboration of the “mortised” zygomatic arch, fusion of postcanine tooth roots, simplification of tooth crowns, elongation of the mandible, and enlargement of the posteroventral flange for the digastric insertion of the mandible.
            Curiously, Allodesmus appears to have gone extinct by the early Messinian or late Tortonian (~9 Ma), based on the age of the youngest known specimens from the Montesano Formation of Washington and the Santa Margarita Sandstone near Santa Cruz. Post-middle Miocene specimens of Allodesmus are also relatively rare: the post-middle Miocene record is effectively restricted to the partial skeleton from the Montesano Fm. of Washington, about a dozen teeth from the Santa Margarita Sandstone near Santa Cruz, and a few teeth from the Monterey Formation of Orange County I saw at the Cooper Center last Fall. In contrast, the late Miocene record of larger pinnipeds is dominated by “imagotariine” and dusignathine walruses like Imagotaria, Gomphotaria, Dusignathus, Pontolis (and two other unnamed dusignathine genera) and the early odobenine Aivukus. Other pinnipeds include the early otariids Pithanotaria starri and Thalassoleon. Interestingly, early and Middle Miocene walruses (e.g. Proneotherium, Neotherium, Pseudotaria) that co-occur with desmatophocids are mostly relatively small bodied, similar in size to large fur seals and female sea lions (Pelagiarctos is a notable exception, although it wasn’t very large). However, in the late Miocene, walruses both increase in body size (the “smaller” walruses like Imagotaria were only the size of large California sea lions, while monsters like Pontolis were five or six meters in length – southern elephant seal sized) but also became more diverse.


Future Directions

Clearly, the issue of the phylogenetic position of Allodesmus amongst pinnipeds is not quite a dead and beaten horse, rather one that has been assaulted numerous times but failed to die. As things stand, we know barely more about the relationships of this species than we did in 1990 – which is not to deride either side of the debate. In my opinion, the answer has not yet been adequately addressed, and more character evidence - and a much broader taxonomic sample - are needed. Smaller studies with limited taxonomic sampling are inherently going to be less adequate than broader approaches, and I think the next big step is going to be putting together a comprehensive phylogeny of all modern and fossil pinnipeds (at least, the ones complete enough to be useful, that is). This is something Morgan Churchill and I are planning on in the somewhat distant future; our first stab at this was presented on a poster at the 2010 SVP meeting in Pittsburg, which showed a somewhat similar topology to that of the Berta and Wyss (1994) paper. As we speak, some promising research is being done by Reagan Furbish, a student of Annalisa Berta at San Diego State University. Reagan had a pretty neat poster about her Master’s thesis work on the phylogenetic position of Allodesmus, which actually won an award for best student poster at the Marine Mammal conference here in Dunedin last December. Needless to say I’m really looking forward to seeing what else she digs up.


An undescribed skull and mandible of Allodesmus sp. from the Monterey Formation, on display at the San Diego Natural History Museum. Does this represent a new species of Allodesmus? Or a previously described species? The short answer is, nobody knows (yet). 
In addition to these ongoing issues, there is a whole lot more material of Allodesmus known now. The late Miocene Allodesmus specimen at the Burke Museum (Montesano Formation, Washington) is still undescribed, and there are numerous isolated teeth in collections at UCMP and the Santa Cruz Museum representing similarly young specimens of Allodesmus from the Santa Margarita Sandstone near Santa Cruz (the latter being an easy project I’ll probably take on in search of “low hanging fruit”). Last fall I saw a partial but nonetheless informative skull (with mandibles and an atlas) of Allodesmus kernensis from Sharktooth Hill at Sierra College; this, and other new specimens from SDNHM (including another nice, partially disarticulated skull), certainly warrant further study. If you read Mitchell’s (1966) paper on Allodesmus, yeah, it’s big and thick and well illustrated, but the skull description is actually quite brief. It’s been supplemented by the descriptions in Barnes (1972), but more material always offers to provide new insights. Another undescribed Allodesmus from the Monterey Formation is on display at SDNHM. There is undescribed Sharktooth Hill Bonebed material at LACM that needs publishing, but I can’t say more about it. Barnes and Hirota (1995) also mention an early Miocene “allodesmine” from the Astoria Formation of all places.


Skulls like this (Allodesmus kernensis, Sharktooth Hill Bonebed, SDNHM) are by no means as impressive as some of the previously published specimens - but even squashed, roadkill specimens like this preserve a hell of a lot of morphology and beg - no, deserve careful study. 
Allodesmus has been arguably oversplit, and the taxon is in dire need of revision. Detailed study of new material – whether from Sharktooth Hill or beyond – will help resolve questions of diversity, biogeography, and phylogeny.
What else can be done? The sample from the Sharktooth Hill Bonebed alone is sufficient enough to permit studies of variation of any number of elements (skulls, mandibles, teeth, postcrania), in addition to providing well-preserved specimens for functional analysis (feeding ecology, muscle attachment mapping, further studies of locomotion) and studies of ontogeny and sexual dimorphism, as well as isotope geochemistry (e.g. Oxygen and Carbon isotopes for studying paleoecology). There is literally a host of avenues for future research – just on a single genus of pinniped. The sky’s the limit – and Morgan and I can’t do all of it! I hope this reaches someone who can help out with the California marine mammal fossil record – there is so much more left to do, even on the best known fossil pinniped.

References

L. G. Barnes. 1972. Miocene Desmatophocinae (Mammalia: Carnivora) from California. University of California Publications in Geological Sciences 89:1-76.

L.G. Barnes. 1989. A new enaliarctine pinniped from the Astoria Formation, Oregon, and a classification of the Otariidae (Mammalia: Carnivora). Contributions in Science, Natural History Museum of Los Angeles County 403:1–26.

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.

L.G. Barnes, D. P. Domning, and C. E. Ray. 1985. Status of studies on fossil marine mammals. Marine Mammal Science 1:15–53.

A. Berta and A. R. Wyss. 1994. Pinniped phylogeny. Proceedings of the San Diego Society of Natural History 29:33–56.

T.A. Deméré and A. Berta. 2002. The Miocene pinniped Desmatophoca oregonensis Condon 1906 (Mammalia: Carnivora), from the Astoria Formation of Oregon; pp. 113–147 in R. J. Emry (ed.), Cenozoic Mammals of Land and Sea: Tributes to the Career of Clayton E. Ray. Smithsonian Contributions to Paleobiology 93

E. D. Mitchell. 1966. The Miocene pinniped Allodesmus. University of California Publications in Geological Sciences 61:1-105.

A.R. Wyss. 1987. The walrus auditory region and the monophyly of pinnipeds. American Museum Novitates 2871:1–31.

Thursday, June 5, 2014

The best known fossil pinniped, part 3: life habits, paleoecology, and biogeography of Allodesmus



An undescribed skeleton of Allodesmus from the Miocene of Japan, on display at the National Museum of Nature and Science in Tokyo.

The abundance of Allodesmus in the Neogene marine record in concert with its completeness made investigation of its paleoecology and life habits inevitable. However, most of what follows is scoured from a few publications, and ample scope for further studies of functional morphology, ontogeny, and sexual dimorphism exist for future researchers.

 
This doesn't really belong anywhere in here, but when I found this strange photo I knew I couldn't leave it out. Ignoring the bizarre pose and composition of the slab and the unecessarily included models, this picture does actually give you an idea of how large Allodesmus was.

Ontogeny and Body Size

A few studies have touched upon growth in Allodesmus, and have mostly discussed issues of age determination rather than growth-related changes in morphology. Mitchell (1966) briefly investigated epiphyseal fusion in Allodesmus, and found that (unsurprisingly), in the forelimb epiphyses fused at the elbow before other parts of the forelimb, and that in the hindlimb, fusion begins at the hip and ankle before progressing to the knee joint (for casual readers, epiphyses are the ends of long bones that begin as separate osteological units and later fuse to the shaft – known as the diaphysis – the radius and ulna have a proximal epiphysis, a distal epiphysis, and the diaphysis; the diaphysis generally composes most of the bone).
            A classic and widely used method for age determination in pinnipeds and other marine mammals is counting periodic growth marks in teeth in sectioned teeth under a microscope. Additionally, in pinnipeds (and presumably other carnivores) preserve a series of annular ridges/grooves in the root, corresponding to periodic growth marks in the cross section of the tooth. Mitchell (1966) was one of the earliest researchers to apply this method to fossil pinnipeds, and sectioned teeth of Allodesmus from the Sharktooth Hill Bonebed. Although the canines of the Allodesmus kelloggi holotype did not yield good results owing to “varying replacement phenomena” (unclear if this refers to an in vivo process or diagenesis), canines of similar size (and presumably root closure) were sectioned and exhibited a minimum of 13 growth marks, suggesting a minimum age of 13 years for Allodesmus kelloggi.
            Allodesmus kelloggi was estimated to be 2.6 meters in length by Mitchell (1966); this is the most complete skeleton of a desmatophocid known, so other Allodesmus (=Allodesminae of Barnes and Hirota, 1995) may be scaled from this species. It should be pointed out here that Allodesmus kelloggi is the smallest known species of Allodesmus. Mitchell (1966) pointed out that other specimens from Shartooth Hill would be much larger (up to 3.35 meters), surpassing even the Northern sea lion Eumetopias jubatus (3+ meters) in size. Taking measurements of other skulls of Allodesmus, small body sizes for Allodesmus sadoensis (2.1 meters) and Allodesmus packardi (2.2 meters) are probable. A much larger body size is indicated for LACM 9723 – the largest known Allodesmus kernensis/gracilis specimen – this individual, scaled up from Allodesmus kelloggi, would have been 3.8 meters in length. Lastly, the positively enormous adult rostrum of Allodesmus sinanoensis (=Allodesmus megallos of Barnes and Hirota 1995) would have been a whopping 4.8 meters in length! To put this in context, this would be an animal the size of the largest male Northern Elephant Seal (Mirounga angustirostris – 4.3-4.9 meters), and surpassed only by the Southern Elephant Seal (Mirounga leonina – 4.2-6 meters).
            Despite having a relatively large sample size from the Sharktooth Hill Bonebed, little investigation of sexual dimorphism has been attempted – and remains a lucrative research topic for future researchers.

Mitchell's (1966) elephant seal-like reconstruction of Allodesmus. Although some have criticized the addition of a proboscis (Adam and Berta, 2001) I don't feel like it's such a bad call myself. However, more time looking at the structure of the prenarial shelf in this pinniped would permit me to make a more informed interpretation.


Life Restoration

This is by far the most speculative part of this post. Mitchell (1966) hypothesized that due to the large size of Allodesmus, and relatively short forelimbs (although that really remains to be established), Allodesmus likely had thick layers of blubber, and further speculated that Allodesmus lacked fur and was possibly hairless like elephant seals. Another observation first made by Mitchell (1966) with the first skull of Allodesmus was that it exhibited a peculiar prenarial shelf, somewhat similar to elephant seals. Based on the size of this prenarial shelf, and the position of muscle attachment scars, Mitchell (1966) speculated that Allodesmus had a short proboscis like extant elephant seals. However, Berta and Adam (2001) suggested that Allodesmus may not have a proboscis, citing as yet unpublished research. The question of whether or not Allodesmus had a proboscis has barely been answered, and future studies could certainly go further.

The teeth of Allodesmus, from Mitchell (1966). J-M are classic examples of "phallic" Allodesmus cheek teeth.
Feeding Ecology

The skull of Allodesmus is quite different from many other pinnipeds. It has one of the proportionally longest palates of any known pinniped, fossil or modern. All of the teeth of Allodesmus are single-rooted with bulbous, simple cheek teeth bearing a single cusp; isolated Allodesmus teeth are frequently found by fossil collectors at Sharktooth Hill and appear “phallic” to many amateurs (check out the photo; you can do the math). The canines are relatively small in Allodesmus in comparison to similarly sized otariids and odobenids (with the exception of the adult “snout” of Allodesmus sinanoensis; =Allodesmus megallos of Barnes and Hirota, 1995). The mandible is relatively gracile but bears a well developed flange for the digastric insertion, as in modern elephant seals (Mirounga). Allodesmus curiously lacks well developed nuchal and sagittal crests as in many fossil and modern otariids and many odobenids, and also has an unusually small coronoid process of the mandible – suggesting reduced temporalis musculature (the temporalis is the primary jaw closing muscle; those of you who are dog owners can feel it by petting the top of your dog’s head while it is chewing; cat owners should not try this). Lastly, the eye sockets of Allodesmus are proportionally enormous; they are so large, that Debey and Pyenson (2011) suggested that Allodesmus was a deep diver, like modern elephant seals.
The lengthening of the palate is probably related to suction feeding (Adam and Berta, 2002), and Allodesmus was reconstructed as a pierce/raptorial feeder by Adam and Berta (2002). The simplification of the postcanine teeth and reduction in size of the posterior postcanine teeth suggests reduced utility of the dentition, potentially even more so than other pinnipeds. The underdeveloped cranial crests and small coronoid process suggests a decreased importance of jaw closing musculature relative to many other pinnipeds. All of this, in concert with the enormous eye size and potential deep diving ecology, in my opinion, suggests a possible suction feeding elephant seal-like habitus. However, it is important to note that craniodental morphology correlates poorly with diet in pinnipeds.

Allodesmus kernensis (=Allodesmus gracilis of Hirota and Barnes, 1995) at the San Diego Natural History Museum reconstructed in a very sea lion like pose. Check out the length of the forelimb - at first glance, it screams "sea lion" in terms of function.
Locomotion

Osteological characteristics of limb bones and the hypothesized monophyletic clade formed by desmatophocids and phocids (Phocoidea) led Berta and Adam (2001) to interpret Allodesmus as a hindlimb-dominated swimmer. However, a subsequent study by former Gingerich student Ryan Bebej (2009) based on proportions of limb bones identified that Allodesmus was most similar to modern fur seals and sea lions, which are forelimb-dominated swimmers. In fact, fur seals and sea lions swim in a somewhat similar fashion to penguins (although have a forelimb that bends more at the elbow). Interestingly, Allodesmus was found to be slightly less aquatically adapted than extant pinnipeds by Bebej (2009), which is borne out by the fact that Allodesmus first appeared within the first 10 million years of the evolutionary history of pinnipeds. Significantly, Allodesmus has an otariid/odobenid like ankle, indicating that this pinniped could terrestrially "walk" as opposed to wriggle like modern earless seals (Phocidae). Modern true seals cannot rotate their ankle forwards, meaning their hindflippers are always pointing posteriorly and cannot be used for locomotion, and so they must wriggle around awkwardly on beaches like a kid trapped in a sleeping bag.

Biogeography

Lastly, Allodesmus is now known from the middle and late Miocene of California, Baja California, Washington, and Japan. This indicates that this genus was widely distributed across much of the Northern Pacific, including most of the west coast of North America. Allodesmus had a circum-North Pacific distribution, paralleled with many other Mio-Pliocene marine mammals (Desmostylus, Paleoparadoxia, Albireo, Kentriodon, Thalassoleon, Callorhinus, Hydrodamalis, Dusisiren, and many others), and many modern cetaceans and pinnipeds. Allodesmus courseni (=Atopotarus of some authors) and Allodesmus kernensis are known from both California and Japan, suggesting that some species of Allodesmus may have enjoyed a wide geographic range. Curiously, desmatophocids never escaped the north Pacific. Why? My hypothesis would be that Allodesmus was cold-water adapted, and unable to cross the warm equatorial waters that serve as a formidable thermal barrier to north-south dispersal even today. Similarly, Allodesmus never invaded the Atlantic, suggesting it was unable to disperse through the Central American Seaway, although many pinnipeds and other marine mammals were able to disperse from the western North Atlantic to the eastern South Pacific during the Miocene.

Next up: part 4, the controversial phylogenetic position of Allodesmus, and future directions for research.

P.J. Adam and A. Berta. 2002. Evolution of prey capture strategies and diet in the Pinnipedimorpha (Mammalia, Carnivora). Oryctos 4:83-107.
L. G. Barnes. 1972. Miocene Desmatophocinae (Mammalia: Carnivora) from California. University of California Publications in Geological Sciences 89:1-76.
 
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.
 
R.M. Bebej. 2009. Swimming mode inferred from skeletal proportions in the fossil pinnipeds Enaliarctos and Allodesmus (Mammalia, Carnivora). Journal of Mammalian Evolution 16:77-97.

A. Berta and P.J. Adam. 2001. Evolutionary history of pinnipeds. In Mazin J.M., Buffrenil V. de (eds), Secondary Adaptation of Tetrapods to Life in Water. Verlag Dr. Friedrich Pfeil, Munich, pp. 235-260.
 
L.B. Debey, and N.D. Pyenson. 2013.Osteological correlates and phylogenetic analysis of deep diving in living and extinct pinnipeds: what good are big eyes? Marine Mammal Science 29:48-83
 
E. D. Mitchell. 1966. The Miocene pinniped Allodesmus. University of California Publications in Geological Sciences 61:1-105.
 

Sunday, May 11, 2014

The best known fossil pinniped, part 2: How many species (...and genera) are there of Allodesmus, anyway?

Last week I summarized the history of research on Allodesmus (and Atopotarus). How many species of Allodesmus exist? And how many genera of desmatophocids are there? On one extreme, one could take the view that there are only two genera – Allodesmus and Desmatophoca – and that Atopotarus, Megagomphos, and Brachyallodesmus are all synonyms of Allodesmus. On the other hand, a more diverse view of the Desmatophocidae would include as many as 10 species in the aforementioned 5 genera. We’ll start with genera – and then look at the species level.

How many genera of desmatophocids are there?

I won’t bother with Allodesmus and Desmatophoca, since these are both clearly “real” and the oldest available names for generic concepts.

AtopotarusAtopotarus is largely diagnosed by the retention of primitive characteristics in comparison to Allodesmus spp. For example, Atopotarus lacks the prenarial shelf of more derived Allodesmus such as Allodesmus kernensis/kelloggi/gracilis, has a less inflated braincase, and retains double-rooted postcanine teeth (premolars and molars). In contrast, the teeth of Allodesmus are single rooted. All these features were listed by Barnes and Hirota (1995) as distinguishing A. courseni from Allodesmus at the generic level. Mitchell (1966) was the first to suggest that Atopotarus courseni was possibly a species of Allodesmus – prior to his description of Allodesmus kelloggi, insufficient cranial and postcranial material was known to really evaluate the generic validity of Atopotarus. This skepticism was echoed by Barnes (1972), Kohno (1996) and Deméré and Berta (2002) – although its generic distinctiveness was endorsed by Barnes and Hirota (1995). I’ve always been on the fence about Atopotarus – it’s barely distinguishable from Allodesmus as it is slightly more plesiomorphic and its morphology – with the exception of the possibly lost second lower molar – could reflect the ancestral morphology of the entire genus. Amongst extant pinnipeds, including phocids – closely related clusters of species (e.g. Zalophus, Arctocephalus, Monachus), with the exception of the Phoca-Pusa-Halichoerus complex – tooth rooting doesn’t vary this much between species, potentially suggesting that Atopotarus might be real. More fossil material of Atopotarus is necessary to further evaluate it, since the holotype is a somewhat flattened articulated specimen exposed in relief in a large slab.


The holotype specimen of Atopotarus courseni, from Downs (1956).

Brachyallodesmus: this genus was erected by Barnes and Hirota (1995) for Allodesmus packardi, the skull from Portola Valley in southern San Mateo County. Features used by these authors to distinguish it from other Allodesmus include canines with an oval cross section (rather than round), an inflated braincase lacking strong nuchal crests, enormous orbits with an extremely narrow intertemporal region, and some primitively retained characteristics such as bilobed premolar roots, a furrow on the side of the braincase marking the position of the pseudosylvian sulcus on the brain, and a less flattened tympanic bulla. This species is arguably much less primitive than Atopotarus courseni, and while I’m on the fence about the generic distinction of Atopotarus, the claim that Allodesmus packardi is generically distinct is spurious in my opinion, and in my preference for taxonomic conservatism (aka lumping), I’ve always held the consideration that this is a species of Allodesmus.
Megagomphos: This genus of desmatophocid was also erected by Barnes and Hirota (1995) for a fragmentary rostrum previously known as Allodesmus sinanoensis (originally erroneously placed in Eumetopias). This specimen is the same size as the largest specimens of Allodesmus from California. Characteristics used by Barnes and Hirota (1995) to elevate it to a separate genus include the lack of a prenarial shelf (like Atopotarus) and the presence of larger canines than other Allodesmus. Kohno (1996), however, identified several features of this specimen suggesting that it was immature, such as unworn teeth that have large pulp cavities and are not completely erupted. In contrast, Barnes and Hirota (1995) thought that this specimen was an adult because of the shape of the tooth roots and purported fusion of the premaxilla-maxilla suture, but didn’t discuss the ontogenetic stage of this specimen any further. In contrast, Kohno (1996) interpreted the specimen to have a large prenarial shelf, eliminating one purported feature excluding it from Allodesmus; similarly, it exhibits single rooted postcanine teeth and no features of the dentition preclude it from being Allodesmus. Furthermore, one Allodesmus synapomorphy – the prenarial shelf – unequivocally links this specimen with Allodesmus to the exclusion of all other pinnipeds. Although Barnes and Hirota (1995) considered this specimen to lack a shelf, it is present but since the specimen is bilaterally compressed and crushed, which has made the shelf appear less apparent than in life. While this specimen has a few minor differences with other described species of Allodesmus such as procumbent, large canines – no features suggest that establishment of Megagomphos was necessary.

In conclusion, evidence supporting the generic distinction of Megagomphos and Brachyallodesmus is limited to non-existent – but Atopotarus may be “real”, although more cranial material is necessary to evaluate Atopotarus.

How many species of Allodesmus?

Allodesmus from Japan: To date, four species of Allodesmus have been described from Japan. These include the aforementioned Allodesmus sinanoensis, the well-preserved Allodesmus sadoensis, and the more fragmentary Allodesmus naorai (the “Mito seal”) and Allodesmus megallos. Allodesmus sadoensis is known from a nearly complete skull and partial mandibles, and is readily distinguished from all other Allodesmus by having anteriorly crowded and procumbent (forward pointing) postcanine teeth, more vertically oriented mandibular symphysis, and lower postcanine teeth without gaps between them. Allodesmus naorai is similar to Allodesmus packardi, and differs only in a few minor features such as having a slightly wider interorbital region and supraorbital processes positioned further posterior – potentially diagnostic features. The fourth species, Allodesmus megallos, was also named by Barnes and Hirota (1995) and diagnosed based on its enormous size, procumbent tusk-like canines and proportionally larger incisors. However, Kohno (1996) independently referred this specimen to Allodesmus sinanoensis, based upon the shared large size, large procumbent canines, and enlarged incisors, and considered this specimen to be an adult – it is substantially larger than the holotype of A. sinanoensis, now recognized to be a juvenile. Furthermore, Kohno (1996) pointed out that both this specimen and the juvenile A. sinanoensis type specimen were from the same rock unit. This specimen, by the way, represents one of the most gigantic of all pinnipeds – it has an estimated skull length of 55-59 centimeters, just a hair smaller than the giant walrus Pontolis (60 cm), and even larger than the double tusked walrus Gomphotaria (40 cm). I think Kohno (1996) makes a reasonable case that this specimen is an adult of Allodesmus sinanoensis, and therefore that Allodesmus megallos is a junior synonym. In conclusion, three species of Allodesmus appear to be known from Japan.

A size comparison with casts of the partial gigantic rostrum of Allodesmus sinanoensis (=Allodesmus megallos) and the type specimen of Allodesmus kelloggi.

Allodesmus from Sharktooth Hill, California: Five species of Allodesmus are known from the middle Miocene of California, and three of them have all been named from the Round Mountain Silt: Allodesmus kernensis, Allodesmus kelloggi, and Allodesmus gracilis. As stated in the previous post, Allodesmus kernensis was described from a partial mandible with an erect canine, a deep mandibular symphysis, and a somewhat double-rooted lower molar. Mitchell (1966) originally drew attention to the observation that the mandibles of Allodesmus kelloggi and other mandibles from the Sharktooth Hill Bonebed consistently differed from Kellogg’s type specimen in having a shallower mandibular symphysis, having a more erect canine, and having a single rooted lower molar. Mitchell (1966) also pointed out that the locality data for the Allodesmus kernensis holotype actually pointed to two different, mutually exclusive localities, and suggested that the locality data indicated that the Allodesmus kernensis holotype was collected somewhat below the stratigraphic level of the Sharktooth Hill Bonebed, lower down within the Round Mountain Silt. Because of these perceived differences, Mitchell restricted A. kernensis to the type specimen, named his new skeleton A. kelloggi, and referred all known Allodesmus material from the bonebed to his new species.


The holotype skull of Allodesmus kelloggi. Check out the size of that orbit!

            Many of these claims were criticized by Barnes (1970, 1972). He pointed out that in the context of variation of modern Zalophus (California Sea Lion), the features identified by Mitchell as separating Allodesmus kernensis from the rest of the bonebed sample are within the range of variation expected for a pinniped species, with the exception of shape of the mandibular symphysis – which varies less within extant Zalophus than it does within the bonebed sample of Allodesmus. Regardless, Barnes (1970) pointed out that all of the morphologic features used by Mitchell (1966) to separate Allodesmus kernensis actually fell within the range of variation of Allodesmus mandibles from within the bonebed itself. Barnes (1970, 1972) then synonymized A. kelloggi with A. kernensis, and referred all known material from the bonebed to A. kernensis. Barnes further pointed out “no conclusive arguments that the holotype of A. kernensis was collected from some formation other than the Round Mountain Silt”. Although this does not really negate Mitchell’s suggestion that the holotype came from an older horizon, Barnes correctly points out that there is uncertainty regarding the A. kernensis type locality – which in my mind means that Mitchell’s hypothesis is speculative. In the context of known Allodesmus variation and the fact that the A. kernensis holotype falls within the range of variation reported for mandibles from the bonebed – I think the idea that the A. kernensis type is more primitive than the bonebed sample falls on its face, and that the hypothesis that A. kernensis was really collected from a lower, older horizon need not be invoked. After all, the type specimen was (thought to be) collected in 1911 by R.C. Stoner, according to the specimen label, or by Charles Morrice (according to Kellogg, 1922), in 1909-1912; locality data were not always accurate in those days. Given the two sets of contradictory data regarding the provenance of the type specimen, any argument being made about the locality of this specimen should be considered to be speculative at best. I speculate that, given how abundant vertebrate fossils are within the bonebed, and how rare they are outside the bonebed, that it is more likely that the specimen was in fact collected from the bonebed and that the locality data is inexact. This seems more reasonable to me, but I note that it is not falsifiable – and that Mitchell’s (1966) arguments are not falsifiable either (although perhaps less parsimonious than my suggestion).


Fifty years of taxonomic disagreement contained in a single photograph. How many species of Allodesmus are represented here? One? Two? or Three? From top to bottom, holotype mandible of Allodesmus kelloggi, cast of holotype of Allodesmus kernensis, and cast of referred mandible of Allodesmus gracilis.
Despite the rather sober arguments made earlier, Barnes and Hirota (1995) indicated that the wider variation within the “Allodesminae” resulted in the recognition that the seemingly minor differences between Allodesmus kernensis and the bonebed sample were in fact meaningful. In the absence of quantitative study (as Barnes, 1970, had done) they resurrected Allodesmus kelloggi – a name which they restricted to Mitchell’s type specimen – and went so far as to establish a third species, Allodesmus gracilis, for the remainder of material from the bonebed. Barnes and Hirota (1995) echoed many of Mitchell’s (1966) arguments and casually dismissed Barnes (1970, 1972) earlier, and in my opinion well-reasoned observations. They further pointed out that the holotype mandibles of Allodesmus kelloggi have a strange, widened flange of bone on the anterior part of the coronoid process, in addition to having a single-rooted lower molar, apparently unique amongst specimens from Sharktooth Hill. However, it is well known that modern pinnipeds have tooth roots that vary quite a bit – the short version is that arctoids primitively have triple or double-rooted premolars and molars, and that in the transition to aquatic life, many pinnipeds have lost their carnassial teeth in favor of simplified teeth for catching fish, roughly similar to what happened with dolphins. Dental simplification, in concert with crowding the teeth in the front of the jaw, has resulted in double rooted teeth of archaic pinnipeds fusing together, generally starting from the front of the jaw. In my 2011 paper on fossil Callorhinus, I noted that there is a fair amount of variation in the tooth roots of extant Callorhinus ursinus (Northern Fur Seal). In the context of extant pinniped dental variation (which is considerably more than terrestrial carnivores, probably because pinnipeds do not chew and thus do not require precise occlusion), this observation on Allodesmus kelloggi does not preclude it from being a member of Allodesmus kernensis.


The holotype skull of Allodesmus gracilis.

Deméré and Berta (2002), although not focused on Allodesmus taxonomy, noted that the occurrence of three species of Allodesmus within a narrow stratigraphic interval in the Round Mountain Silt is a bit hard to swallow, and I agree. I can understand the rationale behind restricting names to seemingly oddball specimens like the holotypes of Allodesmus kelloggi and Allodesmus kernensis – these are decisions done in spirit of taxonomic stability. However, any argument that these three perceived species are distinctive enough to be recognized as separate taxonomic entities needs to be done quantitatively – which has been done exactly once - by Barnes (1970). There is a huge discrepancy between the rather taxonomically conservative conclusions of Barnes (1970) and the rather optimistic splitting of Allodesmus into several genera.


The holotype mandible of Allodesmus gracilis - or a referred specimen of Allodesmus kernensis?

So, how many species and genera are there? I tend to be on the taxonomic lumping side of things, as modern pinnipeds show quite a bit of variation – and keeping this variation in mind, I think a bit of skepticism is in order regarding new taxonomic names for the densely sampled and well published record of pinnipeds from the eastern North Pacific. I think the following list best summarizes my opinions on which genera and species are real:

Atopotarus? Allodesmus? courseni
Allodesmus packardi (syn: Brachyallodesmus)
Allodesmus kernensis (syn: A. gracilis, A. kelloggi)
Allodesmus sadoensis
Allodesmus sinanoensis (syn: Megagomphos sinanoensis, Allodesmus megallos)
Allodesmus naorai


Next up: we still have at least two more parts to this, including the paleoecology of Allodesmus and the phylogenetic position of the family Desmatophocidae.

References

L. G. Barnes. 1970. A re-evaluation of mandibles of Allodesmus (Otariidae, Carnivora) from the Round Mountain Silt, Kern County, California. PaleoBios 10:1-24.

L. G. Barnes. 1972. Miocene Desmatophocinae (Mammalia: Carnivora) from California. University of California Publications in Geological Sciences 89:1-76.

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.

Demere, T. A., and A. Berta. 2002. The Miocene pinniped Desmatophoca oregonensis Condon 1906 (Mammalia: Carnivora), from the Astoria Formation of Oregon; pp. 113–147 in R. J. Emry (ed.), Cenozoic
Mammals of Land and Sea: Tributes to the Career of Clayton E. Ray. Smithsonian Contributions to Paleobiology 93.

T. Downs. 1956. A new pinniped from the Miocene of southern California: With remarks on the Otariidae. Journal of Paleontology 30(1):115-131.

R. Kellogg. 1922. Pinnipeds from Miocene and Pleistocene deposits of California. University of California Publications in Geological Sciences 13(4):23-132.

N. Kohno. 1996. Miocene pinniped Allodesmus (Mammalia: Carnivora); with special reference to the "Mito seal" from Ibaraki Prefecture, Central Japan. Transactions and Proceedings of the Palaeontological Society of Japan, New Series 181:388-404.

E. D. Mitchell. 1966. The Miocene pinniped Allodesmus. University of California Publications in Geological Sciences 61:1-105.