Oregon coast trip with Ray Troll and Kirk Johnson, part 2: fossil localities of the Newport Embayment

We got up early the following morning to prepare for a long day of field work. We had some ambitious plans: we were to check out three of Doug Emlong’s fossil localities, all in one day. This included an area south of Depoe Bay, and the well-known Moloch (pronounced Moolack) Beach north of the Newport Lighthouse. These localities are all exposures of various units deposited within the mid-Cenozoic Newport embayment, an ancient basin that occupied what is now the central Oregon coastline, from Waldport to Lincoln City (or further; I’m unclear as to the limits of the depositional package, but it certainly does not continue to Astoria, as mid-cenozoic rocks in this region are considered part of the Astoria embayment). Marine rocks in coastal Oregon have yielded a substantial assemblage of fossil marine mammals, among other marine (and terrestrial vertebrates). Indeed, we owe much of our knowledge of marine vertebrates from this time and place to the dogged perseverance (if not outright obsession or addiction) of Emlong, and other collectors who followed him like Guy Pierson and James and Gail Goedert. The three formations we visited were the ‘middle’ Oligocene Yaquina Formation, the late Oligocene-early Miocene Nye Mudstone, and the late early-early middle Miocene Astoria Formation. FYI, some paleontologists – myself included prior to this trip – assume that it’s Spanish in origin and pronounced “Yakeena”. Turns out it’s pronounced “Yakwinna”, and it’s named after the nearly extinct Yaquina Indians; an alternate spelling of their language is actually Yakwina. Anyway, now you know. There’s a Yaquina bay, Yaquina Formation, and the Yaquina lighthouse.

Ray and I discuss the finer points of desmostylian posture while Kirk does something practical.

Ray and I are still discussing desmostylian posture while waiting for a table at the Otis Cafe.

 

The spouting horn at Depoe bay, Oregon. We stopped to check this out on our way to the localities.

Before we left for the field, we drove from the Sitka Center to the local favorite ‘Otis Café’. Over an enormous breakfast consisting of the world’s best fench toast and bacon, Ray, Kirk, Sarah, and I discussed the intricacies of reconstructing the posture of desmostylians. Frank Boyden joined us a little late for breakfast. On a whim, Kirk asked the waitress if she knew who Emlong was – and as it turned out, her sister had been a girlfriend of Emlong’s. Apparently, he had asked her out after high school, and she wasn’t interested. He tried again after he got his first payment for his Smithsonian collecting job (which he started in 1967), and bought a car – and then she went out with him. I made sure to buy a T-shirt from the establishment before we left Lincoln County.

 

Kirk and I put together a plan for the day at our first stop.

 

Although we didn't find any fossils, a walk on the beach is likely to turn up all sorts of evidence of modern dead critters - a tufted puffin carcass, in this case. We spotted about a dozen seabird carcasses, including several puffins (Fratercula), murres (Uria), and cormorants (Phalacrocorax). 

Kirk has a habit of scampering up the nearest promontory.

 

Another puffin.

Our first stop was the Yaquina Formation. Emlong collected a number of significant fossils from the Yaquina – by far the most important of which is the type and only known specimen of the toothed mysticete Aetiocetus cotylalveus (not cotylaveus). The holotype skeleton was collected by Emlong in March 1964, and includes a well preserved skull, most of a vertebral column (39 vertebrae), 23 ribs, several loose teeth, part of a sternum, and several chevrons. Emlong originally considered it to be an archaeocete, given the presence of teeth and the lack of derived mysticete features. The remarkable thing is that Emlong, with zero technical background in paleontology – with encouragement from J. Arnold Shotwell and Remington Kellogg – described and named the fossil himself, in his only publication – less than two years after the fossil was dug out of the rock on the beach. It was later identified by Leigh Van Valen as a primitive baleen whale (but I’ll talk about that in a separate post). Other finds from the Yaquina Formation included the holotype of the primitive desmostylian Behemotops emlongi, named after Emlong (later synonymized with Behemotops proteus from the Olympic Peninsula in Washington; this taxon is sort of the “Pakicetus” of desmostylians), and skulls and mandibles of the more derived desmostylian (with a fabulous name) Cornwallius sookensis, which were eventually described by my good friend and colleage Brian Beatty (the species was originally named from the Sooke Formation on Vancouver Island, British Columbia). Lastly, the early pinniped Enaliarctos tedfordi was described from this locality by Annalisa Berta in 1991. Emlong collected the holotype of this specimen – a complete skull – in 1964. We looked around for about a half hour, and didn’t find a damn thing. Then again, the sand level was pretty high.

 

Sarah at Moloch Beach with the Astoria Formation in the background.

We moved to the next locality, a couple miles north – to examine additional outcrops of the Yaquina Formation and the late Oligocene-early Miocene Nye Mudstone. This was near the type locality of Enaliarctos mitchelli, which is from right around the Oligo-Miocene boundary. There was plenty of fossilized wood – probably limonitized or mildly pyritized, as indicated in Emlong’s paper. That’s about all that we found in either the Yaquina or the Nye, though. Despite a long history of important fossil discoveries from this locality, I was beginning to get disappointed with how poorly fossiliferous the localities were – I’m used to fossil localities in central California where literally hundreds of bones, teeth, and bone fragments are found for every skull that is recovered – and on a single trip, a hundred vertebrate fossils can be found after less than an hour of looking. We had visited two localities that had yielded several holotype specimens each, and not found a shred of bone.

 Sarah wading through a field of mostly unfossilferous boulders.

 

 Kirk attempting to crack a concretion the old fashioned way.

We left, hoping that a trip to Moloch beach would prove to yield some better vertebrate material. Moloch beach has an extensive exposure of the early middle Miocene Astoria Formation – which yielded one of the earliest discovered fossil marine mammals from the west coast – Desmatophoca oregonensis, an earlier relative of the large sea-lion like phocoid Allodesmus kernensis. Later, Remington Kellogg and Earl Packard described a new type of baleen whale from Moloch beach, which they named Cophocetus oregonensis. Later, several new pinnipeds were described from the Astoria Formation by Larry Barnes and colleagues: Pteronarctos goedertae, Pteronarctos piersoni, Pacificotaria hadromma, and Proneotherium repenningi; all of these, except P. goedertae, were found at Moloch beach. Subsequently, two more fossil pinnipeds were described from the Astoria Formation: Enaliarctos emlongi (possibly from the Nye Mudstone – near the Nye/Astoria contact) and the tiny phocoid Pinnarctidion rayi. These two were from a separate locality – where the bizarre “oyster bear” Kolponomos newportensis was discovered (…also by Emlong). Oddly enough, Enaliarctos emlongi is one of only two pinnipeds from that locality that don’t begin with P.

 Some beautiful bivalves from the Astoria Formation.

We found a few chunks of rolled bone fragments – but nothing really interesting. Fossil localities with marine mammals are usually pretty easy to prospect – because whales are freaking huge, and have huge bones. It’s usually not hard to find vertebrae and ribs of baleen whales, and again, I was struck by how rare vertebrate remains were. Sure, there were some nice mollusks – but compared to fossil localities in California, like the Purisima Formation at Capitola where there are tons of beautiful mollusks littering the beach – the Astoria at Moloch beach was sort of average in terms of the number of invertebrates. After an hour or two of searching, I finally spotted a huge bone – the first in situ specimen at the locality. It was a large (~1.5 meter long) mandible of a baleen whale, perhaps something like Cophocetus. It’s technically legal to collect concretions from the Oregon coast with vertebrate remains in them – but not to dig bones out from the cliffs or wave cut bench. None of this detracts from Emlong’s legacy – in fact, the inability of three vertebrate paleontologists and several amateurs to find much of anything at any locality after a day of winter field work only makes his discoveries more amazing. My suspicion – and Kirk Johnson’s – is that Emlong capitalized on the fact that concretions sit around for a long time, and nobody before him collected vertebrate bearing concretions in such a systematic manner. There must have been concretions which had accumulated on the beach for thousands of years, and Emlong and subsequent collectors have effectively collected most of that ‘lag’ of concretions, leaving little for current visitors.

 

Ray sketching Kent Gibson's billfish.

After leaving the beach, we visited the nearby home of local amateur fossil collector Kent Gibson, who had found a partial billfish skull in a concretion at Moloch beach (possibly from the Nye Mudstone). It’s some sort of a huge Aglyptorhynchus-like billfish. Kent had an impressive collection, including a beautiful little pinniped skull that could be fairly important, if it were prepared and placed within a museum collection. Ray – being a fish guy – was wanting to see the billfish and other specimens. Upon arriving at Kent’s house, we saw a yard littered with fossils. Ray borrowed some sidewalk chalk from Kent’s kids and started drawing an outline of the billfish’s body as it would have appeared in life, to scale, with the fossil in place. Altogether it was pretty neat. But, we were getting hungry and Frank Boyden had invited us to dinner at his awesome cabin, decorated with his artwork and the artwork of others. Frank showed us some parts of his collection, including original prints by late 19^th century French ‘bohemian’ artist Odilon Redon. At one point, Frank needed to install a railing in his house – instead of installing any old railing, he went to the beach, got a stalk of bull kelp, and casted in bronze – and it is one of the coolest damn things I’ve ever seen. Frank showed us his printmaking studio, which was spectacular, and useful for me as an artist to learn about more involved artistic methods – pencil and paper is my bag, because it’s simple and primitive (and dirt cheap).

 

Frank's "cell phone"

 

We never got a break, even during dinner: Frank had all sorts of bits of animal skeletons. Here kirk and I puzzle over a large fish skull.

Yum!

 

I don't remember what was going on here.

Next up: behind the scenes at the Oregon coast aquarium, Sea Lion Caves, and the conclusion of the trip

Oregon coast trip with Ray Troll and Kirk Johnson, part 1: Lincoln city, Emlong's demise, Sitka Center

A little while ago I realized that I had totally forgotten to talk about our trip to Oregon with Kirk Johnson and Ray Troll last February. I can’t believe it’s been a year already; after our trip to Oregon, my wife and I only had two weeks to finish packing for our three year trip to New Zealand, so I know exactly why I neglected to post about this earlier. Kirk and Ray are working on a new book project, sort of a sequel to “Cruisin the Fossil Freeway”, which was a combination of science, humor, Ray’s awesome art, and the tale of a huge road trip across the American west. This new project changes the focus from the western interior to the Pacific coast of North America – the new book project is titled “Cruisin the Eternal Coastline”, and deals with fossils from Baja California to Barrow, Alaska. Kirk and Ray received a Guggenheim fellowship in 2011 to begin leg work for the project. I first met the dynamic duo in October 2011, literally the day after I found out I had been accepted into the Geology Ph.D. program here at Otago. I showed the guys some of the fossils from my collection, which at the time I was still studying and curating (and are now all in UCMP collections). The next day, we visited a bunch of fossil localities in Santa Cruz, and visited a large mural by Ray at the Long Marine Lab in Santa Cruz.

Ray and Kirk got into contact with me because of my interest in west coast fossil vertebrates – specifically marine vertebrates. Granted, there are all sorts of spectacular land mammal localities as well (and even non-Cenozoic localities, but I won’t dare talk about those…), but the eastern North Pacific margin is home to one of the most extensively sampled marine vertebrate assemblages on earth. The majority of this record is from the coasts of California and Oregon. Ray and Kirk sent me an invitation to join them in coastal Oregon, to track down some of the haunts and old localities of one of my biggest paleontological heroes – Doug Emlong. The guys were even able to cover our travel expenses with their fellowship! Sarah and I left San Francisco, and headed up I-5 and reached Grant’s Pass by midnight. We left early the next morning, having to make it to the Overlook Motel in Lincoln City by 1pm. We just barely had time to take a short detour off Highway 20 to head south to Toledo to visit the type locality of Simocetus rayi, which was described by Ewan Fordyce (my Ph.D. adviser) in 2002. We followed the locality description by my advisor – which is effectively the same as Emlong’s notes. I’m not sure what has happened in the area, but there weren’t any cliffs or exposures of the Alsea Formation anywhere within a mile or two of the indicated point. It’s possible that exposures along the river are now overgrown – as I’ve seen with all sorts of localities in Humboldt County, California.

The type locality of Simocetus rayi - or, somewhere nearby it. Emlong's notes weren't always accurate, and there don't really appear to be any fossiliferous outcrops in the vicinity. Or, any outcrops at all. If there once were cliffs here, they have long since grown over with vegetation.

We finally made it to the motel with ten minutes to spare, just in time for Ray and Kirk’s talk on “Cruisin the Fossil Freeway”. They go on book tours, and have a ~40 minute presentation version of the book – and it’s a real hoot. I had seen it previously at the Bone Room in Berkeley during their bay area leg of the trip in October 2011; it was great, except for the fact that a member of the audience who knew a bit about fossils muttered to themselves and nodded agreement or verbally confirmed everything that came out of Ray or Kirk’s mouths – which was a bit irritating. The attendance at their talk in Lincoln City, however, was enormous – well over a hundred (maybe even two hundred) people showed up, which was phenomenal (both speakers were impressed with the turnout). After the talk, we met all sorts of locals interested in fossils, rocks, and paleontology – and spent at least another hour chatting with folks before leaving the motel. We met several local private collectors, as well as some members of the fossil club “NARG”, who I had heard about for years – they have the oddly non-specific title “North American Research Group”, but they are a seriously organized group of amateurs who are actually able to acquire permits from the state of Oregon to collect, prepare, and curate fossils into various permanent collections. And they do it all as volunteer work; several years ago, they collected a huge balaenopterid mysticete skull from the Empire Formation of Oregon; it’s still under preparation.

I also got to meet the esteemed Frank Boyden of the Sitka Center for Art and Ecology, north of Lincoln City; the center was established in 1970 by Frank and his wife Jane as a residency program for artists, scholars, and academics, with a humble beginning as a summer camp. Upon arriving at the motel, I learned that the talk was being sponsored by the Sitka Center. Frank is a fascinating person to talk to – warm, eccentric, talented, hospitable, and a total luddite. I knew we had some sort of accommodation, but this was one of those things that I had barely planned: Sarah and I were busy as hell with preparations for the move to the southern hemisphere, and Ray and Kirk had told me that everything was taken care of. I guess I was expecting a hotel room somewhere. What I didn’t realize was that Frank was graciously putting us up in some of the cabins at the Sitka Center – Kirk and Ray had their own, and Sarah and I had another. It was a wonderful surprise, totally out of left field. They’re these incredible “sea ranch style” cabins in the Oregon rainforest (sea ranch architecture will be familiar to anyone who’s spent any time on the central or northern California coastline, especially along Highway 1 in Sonoma and Marin Counties). I remember asking Ray whether or not we’d have wireless internet, and Ray reminded me that “Frank has a rock with painted buttons on it for a cell phone.” That was a good enough answer, I suppose. I should have remembered, because earlier at the talk I remember somebody asking him about a cell phone number and he gleefully pulled out his rock "phone".

 

Inside view of our incredible sea ranch style cabin in the Oregon rainforest at the Sitka Center.

To finish our first day of the trip, we tracked down the place where Douglas Emlong died. Using the police report deposited within the Emlong archive at the USNM, we tracked down the exact spot to a small ledge off the side of the road on the Otter Crest Loop between Depoe Bay and Newport, Oregon, just a few hundred yards north of the overlook parking lot. Emlong was a troubled person, and clearly suffered from some psychological issues. There is evidence of obsessive-compulsive disorder, or perhaps bipolar disorder – I’ve had many friends suffering from either, but Emlong’s case seems to have been more severe. He tended to quickly spend money he received from the Smithsonian, and in correspondence with Clayton Ray, he reacted rather extremely after learning that the Smithsonian was unable to appropriate enough funding to continue paying him (sometime around 1977-1978). In June 1980, Emlong returned empty handed from a trip to southern California, and after being back in Newport for less than 24 hours, leapt to his death off a cliff adjacent to the Otter Crest Loop. We only thought it fitting to make a pilgrimage to where the troubled genius met his end.

 

Douglas Emlong's last view. Not a bad one, in my opinion.

 

 

Ray, Kirk, and others reflecting on where Douglas Emlong met his end.

 My wife looking down the cliff - it's about a five hundred foot plunge to the Pacific below.

Next up: A visit to the Yaquina Formation

Was Pelagiarctos a "killer" walrus? Part 5: life restoration

Now that I’ve published research that made the front page of the fox news website, I can consider myself satisfied as a scientist. The Pelagiarctos article has made some additional press, including Science World Report, the Orange County Register, the Otago Daily Times (our local newspaper), and my favorite popular article, titled "Ancient "killer walrus" cuter than originally thought." Also, take a look at Brian Switek's write up on Laelaps.

 

It's in there, in between the articles about the second amendment and how the government 

will be coming after you.

I thought I’d go ahead and explain in a post about the making of the life restoration of Pelagiarctos, and discuss what it may have looked like in life. As detailed in our phylogenetic analysis, Pelagiarctos is most closely related to the late Miocene walrus Imagotaria downsi. Imagotaria downsi is known from the Santa Margarita Sandstone and Sisquoc Formation of Northern and southern California (respectively), and is early late Miocene in age (Tortonian stage – 9-12 Ma). The type specimen of Imagotaria downsi is sort of a cruddy specimen, but a beautiful collection of well preserved fossils was reported by Charles Repenning and Richard Tedford in 1977 from the Santa Margarita Sandstone near Santa Cruz, California. Two skulls including an adult female (“Rep’s Girl” as some marine mammal paleontologists call it) and a subadult male are sea lion like in their morphology. They have long snouts, the skulls are flat-topped, and have low saggittal crests, large canines, and deep mandibles. Although superficially sea lion-like in general form, they lack the supraorbital shelves typical of otariids.

The female skull of Imagotaria downsi from Santa Cruz, affectionately known as "Rep's girl".

The lack of similarity between Pelagiarctos and the modern walrus is evident in its morphology. In the modern walrus, the canines are reduced in size to small pegs, no larger than the premolars (and are thus called ‘premolariform’); the incisors are totally absent, and the “chin” of the modern walrus mandible tapers to a triangular point that lacks teeth and instead has a longitudinal furrow. The transverse tapering of the mandible accommodes the hugely expanded tusks, which for the uninitiated, are the upper canines. The reduction in size of the lower canines presumably also permits enlarged upper tusks – while the complete loss of incisors probably allows an unobstructed pathway for suction into the oral cavity (see the section on odobenid dental and mandibular evolution in Odobenidae in our paper).

 

Rough line drawing of "Rep's girl".

Instead, Pelagiarctos – like Imagotaria – appears to be rather sea lion-like in overall morphology, perhaps something similar to one of the larger, more robust sea lions such as the New Zealand sea lion (Phocarctos hookeri), South American sea lion (Otaria byronia), or Steller’s sea lion (Eumetopias jubatus); the mandible of California sea lions is noticeably smaller and less ‘deep’ than Pelagiarctos. So, we have an overall idea of the shape of the head of Pelagiarctos. To start, I took a line drawing of the skull and mandible of Imagotaria downsi, and in adobe illustrator reduced them to the same mandible size. Then, I took the facial part of the skull, and shortened it to fit the short toothrow of Pelagiarctos. Figuring that the rostrum of Pelagiarctos would have probably been deeper and more robust like the mandible, I also made the facial region more dorsoventrally deep.

 

Cranial reconstruction of Pelagiarctos sp. based on the proportions of Imagotaria downsi.

Then, using this new skull reconstruction, I sketched it in an oblique view by using a reference photo of an Imagotaria skull in the same oblique view, while adding in the changes in proportions. I made sure to sketch it in an angle where I had a photograph of the new Pelagiarctos specimen, so that I could later on digitally overlay the photo of the mandible.

 

 

What did Pelagiarctos look like? More like a sea lion, or a fellow walrus? Due to its early position and early timing in pinniped evolution, it probably had some sort of external ears. It was not a gigantic cold-adapted pinniped like the walrus, so it may have primitively retained abundant fur or hair. It's long whiskers as I've reconstructed it are consistent with a piscivorous habit, rather than the molluskivorous feeding behavior of the modern walrus. My initial black and white graphite drawing is shown here.

So, we’ve got a general shape of the skull and head – but what would it look like? There are still a couple more considerations. For example – would it have had fur? Long vibrissae (whiskers), or short vibrissae? Would it have had thick blubber instead, like the modern walrus? And what about ears – modern walruses (and true seals) don’t have external ears, but sea lions and fur seals (Otariidae) have dinky little ear flaps. Before I continue with this discussion, I must stress that this is all highly speculative. Using the “extant phylogenetic bracket”, and assuming that molecular analyses have correctly identified sea lions and walruses as sister taxa, we can infer that it would look closest to a sea lion or a modern walrus. Okay, that basically includes all of the aforementioned features. The modern walrus is technically closer – but it is a highly derived animal, whereas Pelagiarctos is a very generalized sea lion-like pinniped. I reconstructed Pelagiarctos with external ear flaps to reflect the fact that most early pinnipeds probably had ear flaps or even large external ears (e.g. like an otter). After all, external ears are primitive, and it would be silly to assume that true seals and walruses have lacked ears throughout their evolutionary history. Considering the molecular support for a sea lion + walrus clade, it appears that external ear loss is convergent in the walrus and true seals anyway. What about fur, then? Only a few pinnipeds truly lack dense fur or hair – the walrus, and the elephant seals. The southern elephant seal and the walrus are both high latitude, cold water adapted - but they are also substantially larger than Pelagiarctos. Given the temperate latitude and similarity in size of Pelagiarctos with modern sea lions, which lack fur but have dense hair – it can be parsimoniously reconstructed as “fuzzy”. On that note, I really ought to talk about Heather Liwanag's awesome study on the evolution of marine carnivore fur/hair. Lastly, I reconstructed it with long whiskers because it’s a pelagic hunter – the short, stubby whiskers of the modern walrus are an adaptation for “feeling” benthic invertebrates and sediment.

And the final reconstruction, all colorized and everything. I had a lot of fun doing this reconstruction, and it seemed to do the trick.

Anyway, this concludes my series of posts on the new study by Morgan and I. Hope you enjoyed reading it (and hopefully the actual paper as well).

References-

Boessenecker, R.W. and M. Churchill. 2013. A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos. PLoS One 8(1) e54311. doi:10.1371/journal.pone.0054311.

Epic fossil whale collage

I walked into my labmate Cheng-Hsiu Tsai's office recently and saw that he had a new desktop background - there were some specimens I didn't even recognize. It's a collage he made with nearly every published fossil mysticete he could find (and some modern mysticetes). Tsai, who is currently on a two month research trip to Taiwan, Japan, and Australia - said it would be OK for me to share it here with you all - so, enjoy!

Was Pelagiarctos a "killer" walrus? Part 4: No, probably not. The feeding ecology of Pelagiarctos reassessed

Sorry for the short break – I’ve been fairly busy the last two weeks doing a number of things, but most of all revising a manuscript that was accepted last week on barnacle-encrusted sea lion bones from Oregon. I’m also pleasantly satisfied with additional press attention our Pelagiarctos article got over the last couple of weeks, and the PLOS metrics indicates it’s already gotten 3,000 views, which is quite a few more than my 2011 fur seal article (under 100), although that’s probably because it’s 1) linked to in all the news articles and 2) not paywalled.

Comparison of the holotype (B, C) and referred mandible (A) of Pelagiarctos. From Boessenecker and Churchill (2013).

When Morgan and I started our research on the new specimen of Pelagiarctos, we realized that the most interesting application of the research would be reevaluating the interesting hypothesis by Barnes (1988) that Pelagiarctos thomasi was a specialized macrophagous predator. To recap, Barnes interpreted this novel hypothesis based on several lines of evidence: 1) Pelagiarctos thomasi is relatively rare in the Sharktooth Hill Bonebed relative to other pinnipeds (apex predators are rare because they require a large population of prey items to subsist upon), 2) sharp postcanine teeth roughly similar in morphology to those of bone-cracking hyaenids and borophagine canids, 3) a fused mandibular symphysis, suggesting an adaptation towards high bite force, and 4) large body size. In addition to these interpretations, Barnes (1988) further interpreted all the isolated teeth as being from males – as the holotype “chin” has large canines, and at least one of the postcanine teeth slipped right in to the empty alveolus of the holotype. The rest of the postcanines are of similar size, suggesting to Barnes that they were all from one gender. Most pinnipeds – and all fossil walruses for which we have sufficient sample sizes (even wee little Proneotherium) are sexually dimorphic, with larger males. Furthermore, one of the holotype canines was broken in life and then worn from continued use, which Barnes (1988) interpreted as the result of male-male combat. Barnes further speculated that the lack of females could be caused by geographic separation of sexes – certainly an intriguing possibility, but difficult to test with such a small sample size.

An example of a vagrant pinniped: a leopard seal that wound up on a New Zealand beach. Apparently this happens somewhat often, but regardless - New Zealand is not in the normal range of this animal. From keaphotography.org

We identified several other hypotheses which could just as parsimoniously explain the rarity of Pelagiarctos within the Sharktooth Hill Bonebed. Given the extremely large sample size of fossil vertebrates from the bonebed, and a century of intensive collecting, the rarity is probably a real phenomenon and thus probably not a result of preservational bias (least of which because Pelagiarctos is a large animal and has a higher preservation potential than the smaller but numerically more abundant Neotherium). Numerous studies of modern pinnipeds have demonstrated that they are prone to vagrancy – in the ocean, after all, it’s easy to get caught up in currents or forage further away than other members of your species. It’s also possible that Pelagiarctos was simply a pelagic, offshore pinniped, rarely straying into coastal waters off Orange County (“Topanga” Formation) or the Temblor Sea (Sharktooth Hill). Furthermore, the Sharktooth Hill Bonebed was deposited over a protracted period of time (~700,000 years) due to a depositional hiatus, and it’s possible that a short period of time could have seen introduction of Pelagiarctos (from further south, north, or further out in the Pacific) along with a brief change in climate, ecology, or circulation.

 

A sea lion and a fishy smorgasbord. Photo by David Doubilet.

The fused mandibular symphysis is a bit more ambiguous. The only modern pinniped with a fused symphysis is the extant walrus Odobenus rosmarus, and it’s not immediately clear why, or how it could be adaptive relative to feeding. My hunch is that it’s a secondary consequence of having a pachyosteosclerotic mandible – the lower jaw of Odobenus is thickened around the chin and dense, and development of this may have resulted in symphyseal fusion. The earlier walrus Alachtherium/Ontocetus has an unthickened chin and lacks fusion – but Valenictus chulavistensis (the strange sister taxon of Odobenus) has a fused symphysis, and also lacks a thickened “chin”. Extreme pachyosteosclerosis of the skull and mandible in Odobenus has been suggested as a possible adaptation for keeping the head negatively buoyant during benthic foraging. One other fossil odobenid has a fused symphysis – Dusignathus seftoni from the San Diego Formation. It’s not even clear what Dusignathus ate, so it’s not a very good analogue either. Barnes (1988) argued that a fused symphysis in Pelagiarctos thomasi suggested and adaptation for large bite forces – however, carnivorans with high bite forces such as borophagine canids and hyaenids (which Barnes compared the dentition of Pelagiarctos to), as well as sea otters – all have unfused symphyses, possibly to allow slight movement of the mandibles so as to avoid tooth damage (Scapino, 1981). So what was mandibular fusion in Pelagiarctos thomasi for? Who knows! That’s for someone else to figure out. Besides, the new specimen didn’t have a fused symphysis anyway.

 

Comparison of calculated trophic level and body mass in pinnipeds. Lower trophic level corresponds to feeding upon benthic invertebrates, and high trophic level corresponds to eating large fish and cephalopods. From Boessenecker and Churchill (2013).

 

A walrus after a successful seal kill. These events have only been witnessed a few times by humans. Apparently, walruses will use their powerful suction normally reserved for mollusks to literally suck the meat right from the bones. From moblog.net.

  

 Another gory shot of a walrus feeding on a poor seal. From Vlasman and Campbell, Diseases and Parasites of Mammals of the Eastern Arctic.

We reinvestigated the issue of body size as well. Morgan has been working on a method to estimate the body mass of fossil pinnipeds, and his preliminary results indicated that the length of the lower toothrow is the single best predictor of body mass in a dataset of modern pinnipeds (fortunate for us, since all we had was a mandible to work with). Morgan was able to estimate the body mass of Pelagiarctos sp. at approximately 350 kg (~770 lbs), which is similar to some modern sea lions (male South American sea lions, California sea lions). There are much larger sea lions, however – the Steller’s sea lion (Eumetopias jubatus), which weigh up to 1,150 kg (2,500 lbs). Steller’s sea lion is the fourth largest pinniped (after the two elephant seals and the modern walrus), but is not a macrophagous predator: it feeds predominantly on fish, although it will occasionally prey upon juvenile pinnipeds. The modern walrus also occasionally preys upon juvenile seals and marine birds – yet it is clearly adapted and specialized for mollusk predation. All large bodied otariids predominantly eat fish as well, and many adult male sea lions of other species as well will also occasionally consume warm blooded prey when given the opportunity. Morgan further investigated this by calculating the trophic level of modern pinnipeds and plotting it relative to body mass. The result is that there is no apparent trend between body mass and diet – with one exception: the largest pinnipeds fed both at the high and low trophic levels (e.g. fish, cephalopods, as well as benthic invertebrates – e.g. walruses and bearded seals). In other words, large body mass doesn’t necessarily indicate anything specific about feeding ecology or diet. A previous analysis by Peter Adam and Annalisa Berta (2002) only found a very poor correlation between morphology and diet. That evidence of adaptations for macrophagy is lacking within pinnipeds is highlighted by the leopard seal: it does not use its postcanine teeth to feed upon penguins and seals, and only uses them for filter feeding for krill the rest of the year (8 months or so out of the year). When it feeds upon large bodied prey, it nips with its incisors and canines – which are not really any different from those of fish-eating pinnipeds. In other words, the only modern pinniped which could be argued to be a macrophagous apex predator only has dental specializations for feeding upon krill.

Arguably the only macrophagous pinniped - the leopard seal spends most of the year eating krill, and doesn't use its delicate postcanine teeth for killing penguins and seals, and instead only for filter feeding. Figures from Hocking et al. (2013).

So, not a "killer" walrus after all, but still a pretty intimidating beast.

So what did Pelagiarctos feed on? Probably fish, cephalopods, the normal menu for large bodied pinnipeds. It very well probably did feed upon warm blooded prey – occasionally, anyway (again, like modern pinnipeds). We’re not arguing that Pelagiarctos did NOT eat warm blooded prey – rather, we’ve made the case that Pelagiarctos lacked any adaptations which would lend themselves to macrophagy. One last point of interest – within the Sharktooth Hill Bonebed, Pelagiarctos is not even the largest pinniped; it’s dwarfed by Allodesmus, which Morgan estimated at 1400 kg (~3,000 lbs)! That’s just enormous (and approximately ¾ the size of modern northern elephant seals). Allodesmus, on the other hand, had enormous orbits possibly indicating deep diving adaptations (to which its large body size may have helped with as well), and a long snout with simple teeth – a definite contrast to the short “bulldog” face and dentition of Pelagiarctos.

References:

Adam PJ, Berta A (2002) Evolution of prey capture strategies and diet in the Pinnipedimorpha (Mammalia, Carnivora). Oryctos 4: 83–107.

Barnes LG (1988) A new fossil pinniped (Mammalia: Otariidae) from the middle Miocene Sharktooth Hill Bonebed, California. Contributions in Science, Natural History Museum of Los Angeles County 396: 1–11.

Boessenecker RW, Churchill M (2013) A Reevaluation of the Morphology, Paleoecology, and Phylogenetic Relationships of the Enigmatic Walrus Pelagiarctos. PLoS ONE 8(1): e54311. doi:10.1371/journal.pone.0054311

Hocking, D.P., Evans, A. R., and E.M.G. Fitzgerald. 2013. Leopard seals (Hydrurga leptonyx) use suction and filter feeding when hunting prey underwater. Polar Biology 36:2:211-222.

Scapino R (1981) Morphological investigations into functions of the jaw symphysis in carnivorans. Journal of Morphology 167: 339–375

Was Pelagiarctos a "killer" walrus? Part 3: new specimen from Orange County

In early spring 2011, just as I was finishing up my master’s degree at Montana State, I received an email from Tom Deméré, the paleontology curator of the San Diego Natural History Museum, inviting Morgan and I to study a new fossil of Pelagiarctos from the “Topanga” Formation. Fortunately, I would get a chance to examine it closely in person soon afterward – in June, I would be attending and presenting my master’s taphonomy research at the 6^th triennial conference on secondary adaptations of tetrapods to life in the water (usually abbreviated SATLW or simply referred to as the aquatic tetrapods conference), which was being hosted by Tom Deméré and Annalisa Berta at San Diego State University and the museum.

Although I had successfully delivered my master’s defense presentation and graduated without a hitch a month and a half prior, I was still nervous to give my presentation because it was in front of a totally different audience – technically, the conference was about secondary adaptations, and I was giving a talk on taphonomy. However, I tooled it towards what we can reasonably infer from the marine vertebrate fossil record, including about exactly how aquatic organisms were based on their preservation – which, I concluded at the time was not much. The talk was also fairly long; although I had 18 minutes to speak, which is fairly long, I had not had the time to shorten it. 36 hours before driving down I-5, I was on the beach at Bolinas prospecting with Dick Hilton when I got a funny phone message from Tom ‘asking’ me if it would be okay to move my talk to the first day; so I said my goodbyes to Dick and raced home down Highway 1 so I could spend a day and a half polishing the presentation off. And then worried half the drive down I-5 that I didn’t shorten it enough.

 

  

A comparison of the new Topanga Formation specimen (A) and the holotype (B) of Pelagiarctos.

 

The talk went without a hitch, and later in the conference Morgan and I were able to sequester a few hours in the SDNHM type room to examine the new specimen of Pelagiarctos. It consisted of a fragmentary pair of mandibles, with the left mandible being nearly complete and having much of its dentition (missing only a premolar, the two molars, and an incisor). Unlike the type specimen from Sharktooth Hill (which Morgan and I got a chance to examine in person at LACM in January 2012), these mandibles were not fused together at the symphysis (intermandibular joint). Symphyseal fusion is not common in modern pinnipeds, where it is restricted to the modern walrus. I’ve also seen pathologic (diseased) mandibles of modern otariids where, due to some bone disease, the symphysis has fused along with a large mass of bone at the chin, accompanied by incisor and canine loss.

 

  

 The left mandible of the Topanga Formation specimen of Pelagiarctos. From Boessenecker and Churchill (2013).

The teeth present in the new specimen confirm that the large teeth referred to Pelagiarctos thomasi by Barnes (1988) were correctly referred. It’s not so surprising, since you could predict the mandible shape from the teeth: they are like giant versions of Neotherium teeth, and the mandible is like a giant Neotherium jaw. I never really doubted Barnes’ identifications – but it was nice to confirm them. The mandible of this new specimen is damned huge – it’s wide, deep, with a short toothrow. The canines are robust, again with grooves on the lateral and medial surfaces, giving the canine a figure-eight shape in cross section. The premolars are large, primitively retaining what’s called the metaconid cusp; most modern pinnipeds have teeth that are unicuspid (single cusp, usually conical), with small anterior and posterior accessory cusps in otariids. The main cusp (on lower postcanine teeth) is called the protoconid. The anterior and posterior cusps are the remnants of the paraconid (anterior) and hypoconid (posterior) cusps. The metaconid cusp is a fourth cusp which is present in many primitive pinnipeds, such as the early enaliarctines, as well as Proneotherium, Neotherium, and Pelagiarctos. The metaconid is located just behind the principal cusp (protoconid). Many modern phocids primitively retain all four cusps – the harbor seal is an excellent example. The crabeater seal additionally bears a number of extra “neomorphic” (=new or novel structure) cusps on the posterior tooth crowns, which are used for filter feeding.

 

 

The dentition of the Topanga Formation specimen. From Boessenecker and Churchill (2013).

More details of the dentition of the Topanga Formation Pelagiarctos, from Boessenecker and Churchill (2013); I had a fun time drawing the medial view of those teeth.

In addition to having these primitive features, a couple of new features not seen in earlier walruses are present: a lingual cingulum with small little “crenulations” forming a sawtooth type pattern, and the presence of a labial cingulum. A cingulum is a thickened ridge of enamel at the base of a tooth crown. Pelagiarctos is the only walrus with a labial (cheek side of the tooth) cingulum, and only one other walrus has a crenulated lingual (tongue side of the tooth) cingulum – the late Miocene walrus Imagotaria downsi. At this point the uninitiated reader might ask ‘what exactly makes this thing a walrus?’ The truth is, for the earliest known walruses, the only synapomorphies allowing identification as a member of the Odobenidae (walrus family) are skull features. Many of the features of the known specimens of Pelagiarctos appear in some sea lions – such as a mandible that is deepest near the canines. Although the fossils don’t have any specific features that are diagnostic at the family level – several features of the dentition are only found in early diverging “imagotariine” walruses. The Imagotariinae was a subfamily named by Ed Mitchell and used extensively in various papers by Barnes, but as pointed out by several studies over the past two decades it is a paraphyletic assemblage of primitive walruses. Nevertheless, it is a useful vernacular term; imagotariines are sea lion-like with primitive dentitions, and ranged in size from harbor seal size (Proneotherium) to elephant seal size (Pontolis magnus).

 

 

 

Comparison of walrus mandibles, including the Topanga Fm. Pelagiarctos specimen, Imagotaria downsi from the late Miocene Santa Margarita Sandstone of Santa Cruz County, Proneotherium repenningi from the early middle Miocene Astoria Formation of Lincoln County, Oregon, and Pontolis magnus from the late Miocene Empire Formation of Coos County, Oregon. From Boessenecker and Churchill (2013).

 

Because our new specimen was more complete than the holotype, we were able to include Pelagiarctos within a phylogenetic analysis for the first time. Previous analyses did not use many mandibular characters, so at first we constructed a matrix which focused on mandibular and dental characters, and only used pinniped species known by lower jaws (i.e. we didn’t include some species for which jaws were unknown). This meant we didn’t initially include the early walruses Prototaria and Pseudotaria from Japan. We originally did this because we felt we’d get more accurate results than if we included Pelagiarctos in an analysis where it couldn’t be coded for any cranial characters – it was a reasonable hunch at first. One of our reviewers suggested we use a more comprehensive dataset, so we merged our data set with that of Naoki Kohno’s (2006) analysis for his Pseudotaria muramotoi paper. We ended up with fantastic results, and better support for some of the relationships.

 

 

Cladograms from Deméré (1994), Kohno (2006), and our new study showing the varying position of Pontolis (underlined in red).

Most of the relationships in our analysis are consistent with previous studies like Deméré (1994), Deméré and Berta (2001), and Kohno (2006), with one exception. In Deméré (1994), Pontolis magnus grouped as a dusignathine walrus, and closely related to Dusignathus itself. In Kohno (2006), Pontolis instead formed a sister taxon relationship with Imagotaria. The Imagotaria-Pontolis clade is only one node below the dusignathines, so admittedly it is not a far distance. In our analysis, however, Pelagiarctos formed a sister taxon relationship with Imagotaria instead, based on two features: grooved canines, and a crenulated cingulum. Neither of these features are present in Pontolis. Instead, Pontolis plotted out as the last diverging “imagotariine” and the sister taxon to the dusignathine + odobenine clade – in other words, intermediate between the phylogenetic hypothesis of Deméré (1994) and Kohno (2006). It’s sort of a compromise between the two, in a way. Obviously, there are more cranial characters that need to be explored and new walruses to describe, so there is clearly further scope for a more comprehensive study of walrus phylogenetics, which is in the early planning stages.

Next up: the dramatic conclusion to this series on the new publication, focusing on the feeding ecology of Pelagiarctos, and the life restoration.

References:

Barnes LG (1988) A new fossil pinniped (Mammalia: Otariidae) from the middle
Miocene Sharktooth Hill Bonebed, California. Contributions in Science,
Natural History Museum of Los Angeles County 396: 1–11.

Boessenecker, R.W. and M. Churchill. 2013. A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos. PLoS One 8(1) e54311. doi:10.1371/journal.pone.0054311.

Deméré TA (1994) The family Odobenidae: a phylogenetic analysis of living and
fossil forms. In: Berta A, Deméré TA, editors. Contributions in Marine Mammal
Paleontology honoring Frank C Whitmore, Jr: Proceedings of the San Diego
Society of Natural History. 99–123.

Kohno N (2006) A new Miocene odobenid (Mammalia: Carnivora) from
Hokkaido, Japan, and its implications for odobenid phylogeny. Journal of
Vertebrate Paleontology 26: 411–421.