Southern California Research Trip, Part 3: Natural History Museum of Los Angeles County (collections)

The purpose for our trip to visit the LACM collections was to examine a large collection of pinniped fossils housed there. Curator Emeritus Dr. "Larry" Barnes has been studying fossil pinnipeds since his master's thesis in the late 1960's (which he published in 1972, on Allodesmus and other desmatophocid pinnipeds), and has researched a wide variety of fossil pinnipeds including the early diverging and 'primitive' enaliarctines (a paraphyletic group of early pinnipeds), the relatively large and aberrant desmatophocids (an extinct group of phocoids known only from the North Pacific), all manners of fossil walruses, and fossil sea lions and fur seals. Larry has named quite a few fossil pinniped taxa from the northeastern Pacific region (Enaliarctos mitchelli, Pteronarctos goedertae, Pteronarctos piersoni, Pacificotaria hadromma, Desmatophoca brachycephala, Allodesmus gracilis, Proneotherium repenningi, Pelagiarctos thomasi, Gomphotaria pugnax, and Proterozetes ulysses), and there are a whole slew of holotype specimens to look at at the LACM - including a number of other important finds, including crania and jaws of the walrus Imagotaria downsi and the even earlier Neotherium mirum (but not quite as old as Proneotherium...). Our goal was to photograph all of these skulls and jaws, and take all sorts of measurements of them for our research. Between Morgan and I, we took about 5 gigabytes of photographs of these fossils. At the moment, we have two concurrent research projects which will soon be culminating in submittable manuscripts: a phylogenetic analysis of fossil and modern sea lions and fur seals (Otariidae; Morgan gave a talk on this at SVP this last fall), and another project describing some new material of the extinct "killer" walrus Pelagiarctos, originally described by Larry Barnes from the Sharktooth Hill Bonebed, and discovered by LACM head preparator and all around fun guy Howell Thomas. At bare minimum, we needed to examine, photograph, and measure the holotype "chin" and the referred teeth. Anything else we got done was a bonus - and our bonus included looking at dozens and dozens of skulls, jaws, and teeth of various other pinnipeds.

The hollywood hills can be seen very well from the prep lab, which is several floors up. You can just make out the hollywood sign below the top of the mountains.

The holotype "chin" of Pelagiarctos thomasi.

A referred lower left third or fourth premolar of Pelagiarctos, published by Barnes (1988).

My wife borrowed some of the clay we used for propping oddly shaped specimens up during photography and made a walrus and a manatee; the manatee even has
motorboat propeller scars (just for J. Velez-Juarbe!)

A referred lower jaw of Neotherium mirum from the Sharktooth Hill Bonebed, published by Barnes (1988); this is the only other early walrus from the middle Miocene bonebed.

My wife happened to find a book of 3D cat photos with 3D glasses. Don't ask.

Three different jaws of Allodesmus from the Round Mountain silt; but how many species? According to Barnes, there are three species: the topmost is the holotype of Allodesmus kelloggi, the middle is the holotype of Allodesmus kernensis, and the bottom one is Allodesmus gracilis. Others would lump all these in to Allodesmus kernensis (which would have taxonomic priority).

Three different early walruses! From left to right, they are Proneotherium repenningi from the Astoria Formation of Oregon (early Middle Miocene), Neotherium mirum from the Sharktooth Hill Bonebed of California (late Middle Miocene), and Imagotaria downsi from the Santa Margarita Sandstone (early Late Miocene) of Santa Cruz County, California.

The beautifully preserved holotype skull of Pacificotaria hadromma from the Astoria Formation of Oregon. According to Berta (1994), this may be a junior synonym of Pteronarctos.

Morgan and I conducting research amid a chaotic mess of fossil pinnipeds and other paleontological debris.

Downtown Los Angeles from the window in the prep lab. The US Bank tower can be seen in the middle. If you recall, it was blown to smithereens in Independence Day.

The rostrum and upper dentition of a referred snout of Desmatophoca oregonensis.

Morgan photographing the obscenely gigantic jaw of the bizarre double tusked behemoth of a walrus Gomphotaria pugnax. Seriously, that thing is offensively large.

The holotype skull of Allodesmus kelloggi, described by Ed Mitchell in the mid 1960's from the Sharktooth Hill Bonebed.

An undescribed late Pleistocene jaw of a California sea lion, Zalophus sp., from the Newport Bay mesa.

Last, but not least, another shot of those three walruses -
Proneotherium, Neotherium, and Imagotaria.

What's up next? One or two more posts on the southern CA trip including the Page Museum as well as the Santa Barbara Museum of Natural History, and eventually, I should probably try and cover some recent marine mammal research, I still have to cover a paper I got published on our wedding day, Kolponomos, and a bazillion other things.

Dead baby fur seals at the California Academy of Sciences

Well, it’s been over a month since I’ve posted anything. It’s been a busy winter – in the mean time, my wife and I have celebrated Thanksgiving in California with my family, and have been in Montana for the last week with her family. I’ve been typing like a beast (30 pages for one manuscript just since I’ve been back in Big Sky country) over the last month or so. I’ve been working on my longest manuscript yet (not including my thesis, however it will soon overtake it), which as of this morning reached 110 pages. Additionally, we’ve been trying to get certain things ready for our imminent move to New Zealand. Just prior to Christmas vacation, I spent a couple of days visiting the Ornithology and Mammalogy collections at California Academy of Sciences.

A menagerie of bird and mammal skeletons and mounts.

A giraffe skull sits next to the sign in book.

A row of shelving filled with fur seal and sea lion skulls and skeletons.

A beautiful mounted skeleton of a sea otter (Enhydra lutris).

I’ve been making a couple visits per year to Cal Academy since 2006; I originally visited when the new building was under construction, and the academy (exhibits, departments, and all) were at the temporary storage facility in SoMa (South of Market in Downtown San Francisco, for the non Bay Areans) to check out their collection of Purisima Formation fossils, and to utilize their ichthyology and mammalogy collections to identify shark teeth and pinniped bones from various Miocene and Pliocene strata from Northern California.

A bunch of large mysticete vertebrae awaiting curation.

A pilot whale (Globicephala macrorhinchus) skull in the CAS collections.

On previous visits, I’ve searched the Mammalogy collection of skeletons to make comparisons with modern and fossil bones and teeth of fur seals, walruses, pilot whales, porpoises, and baleen whales. In 2010, I collected some (relatively basic) data on the variation of tooth root lobe morphology in northern fur seals (Callorhinus ursinus) for comparison with fossil fur seals, which I published in JVP earlier this year. A current project I am working on is writing up an entire marine vertebrate assemblage (~200-300 fossils), and I am working on a lengthy manuscript on the marine mammal compliment of the assemblage. Needless to say, the large and very well curated collection of marine mammal skeletons at California Academy of Sciences has been indispensable throughout this endeavor, and has made many fossil identifications possible and paved the way towards insights into marine mammal osteology.

Many crania and jaws of the Northern Elephant Seal (Mirounga angustirostris) are too large for storage boxes and sit right on the shelves.

A walrus (Odobenus rosmarus) skull with two baculi thrown in for good measure (no pun intended).

A bunch of boxes full of Galapagos Sea Lion skeletons (Zalophus californianus wollebaeki).

On my most recent visits, my objectives were threefold: first, to take photographs of many extant species of otariids (fur seals and sea lions) for a morphobank project with my colleague Morgan Churchill; second, to photograph nearly every skeletal element from an adult northern fur seal in order for comparison with fossil fur seals from California (e.g. Thalassoleon, which has previously been hypothesized to be closely related to Callorhinus); and third, to photograph and examine lower jaws of neonatal and fetal fur seals and sea lions.

Several drawers filled to the brim with boxes of small (fetal, neonatal, and juvenile) otariid skulls. Most of these are Callorhinus ursinus.

I won’t get into the specifics quite yet, nor will I talk about the fossils that spurred my curiosity regarding the third subject – I’ll only say that it is pretty damn neat if I may say so myself. That being said – I am very interested in the morphology of deciduous (milk) teeth in young fur seals, as well as the timing of molar and premolar eruption in the lower jaws of these animals. I’ll briefly mention that modern pinnipeds are a bit weird in that they (like most) mammals have milk teeth, but they are often shed before birth, so that the pups are born with a full set of adult chompers. Their milk teeth have a very reduced functional period, and additionally are reduced to tiny little pegs (unlike the milk teeth of terrestrial carnivores). Although they still develop milk teeth, pinnipeds are trending toward monophyodonty – that is, having only one set of teeth as opposed to two (diphyodonty). Cetaceans are monophyodont, and pinnipeds are an excellent example of a second clade of marine mammals following the same evolutionary trend.

A baby fur seal head (Callorhinus ursinus).

A neonatal Callorhinus ursinus skull in lateral view.

In order to examine the tiny milk and permanent teeth of these pups and fetuses, I brought along my new toy – a small, portable, USB powered digital microscope which plugs into my notebook laptop (…another new toy, which I’m using from a secure location in Montana). It displays the image on the screen, and can acts as a camera as well. Fortunately, there is a button to take a picture with in the software, rather than having to manually press a button on the microscope (which, due to its small size, usually jiggles it and screws up the picture). At an earlier UCMP visit in October, I was able to take around 200 photos of 100 tiny fossil specimens in a little over two hours. With the digital microscope, I was able to take a bunch of photos of milk and permanent teeth from nearly a dozen or so specimens of northern fur seal (Callorhinus), California sea lion (Zalophus), and Steller’s sea lion (Eumetopias). Unfortunately, there weren’t any northern fur seal fetuses, or specimens with deciduous premolars – but the data for sea lion fetuses I collected was more than sufficient to answer my fossil-related queries.

Yours truly using my digital USB microscope to examine the morphology of

fetal and neonate fur seal teeth; this specimen is a Northern Fur Seal (Callorhinus ursinus).

Milk teeth and unerupted adult teeth in the lower jaw of a California sea lion (Zalophus californianus) fetus.

October pinniped excavations

Dick Hilton and I excavating a pair of fur seal (Thalassoleon) dentaries from the base of the cliff.

A famished yearling California Sea Lion on the beach.

The weekend before the annual meeting of the Society of Vertebrate Paleontology in Las Vegas, my wife and I joined Dick Hilton from Sierra College for what we assumed would be a routine visit to the Purisima Formation at Point Reyes. We drove up on a Friday night, and cooked hot dogs at the campground with Dick, and set up our tent for the weekend. The following morning, we set out along the shoreline, and within five minutes, found what appeared to be a pinniped skeleton. Since we wanted to get on to more prosperous localities further down, we left it there with the intention of digging it up the following day (Sunday).

My wife pointing to something tiny she is proud of finding...

It's a beautiful fur seal (Thalassoleon) molar! She has a real eye for finding things like tiny pinniped and shark teeth, which is why I keep her around.

Dick Hilton trying to explain something to my wife and I. At least I hope he was talking to my wife, because it sure looks like I wasn't paying attention.

As we headed further on down to the good section of shoreline, I found a well preserved porpoise earbone (petrosal), and a few other odds and ends. Not too long afterward, and nearly at the same time, Dick spotted a couple bones eroding out with an associated tooth, and my wife spotted a well preserved fur seal tooth (Thalassoleon), only a few meters away. It took us the better part of an hour to dig the bones up – which turned out to be a pair of associated fur seal dentaries! Unfortunately, neither specimen had any cheek teeth, but one did have a broken canine. Either way, only the middle chunk of the dentary is preserved in the holotype of Thalassoleon macnallyae (from the same locality), and these are the most complete and well preserved jaws of this taxon now known. We hiked down the beach a little further, and collected a couple of pinniped limb elements – a proximal end of a tibia, and a metatarsal. After collecting these, we headed back towards the cars. On our way back, I spotted a string of a dozen articulated pinniped vertebrae – a second skeleton we would have to excavate the following day.

A cast of the holotype skeleton of Parabalaenoptera baulinensis on display at the visitor center.

For comparison, there is also a skeleton of an adorably tiny (~15 feet long) minke whale (Balaenoptera acutorostrata) on display as well.

My wife examining some baleen (presumably from a balaenopterid) at the visitor center.

We also finally had a chance to visit the visitor’s center; previously, I had always been there on a weekday, when the center was closed. I was particularly excited to check it out because it has one of the only known casts of the holotype skeleton of Parabalaenoptera baulinensis (which was excavated from the Santa Cruz Mudstone at a nearby locality) on display – there is one other, but it is at the College of Marin in Kentfield, and is falling apart and badly needing repairs.

My wife decided she was done, and decided to spend the day reading A Game of Thrones on the beach and napping and taunting birds all day.

On the second day, we spent about seven hours excavating the first pinniped skeleton, which resulted in about 100 pounds of tin-foil jackets. This skeleton is probably of a large fur seal or small walrus, and the skeleton was completely disarticulated; as soon as we were close to removing one bone, another would be under it, or behind it. There were probably about two dozen or so bones in the cliff that we excavated. At about 4 in the afternoon, we wrapped up the first excavation, and walked down the beach to relocate the articulated skeleton. It took a while to relocate it, but as soon as we did, we started excavating it in a large block. Thanks to the specimen being articulated, we were able to finish this excavation in a little over an hour. Once we got back to the car, we loaded up nearly two hundred pounds of fossils we had collected in only two days in the field; furthermore, the most ridiculous aspect of the weekend was that by weight, cetacean fossils comprised less than 1% of our haul (only one specimen). For the uninitiated – pinniped fossils are relatively rare, and my master’s thesis sample of specimens indicates that there is a 4:1 ratio of cetacean fossils to pinnipeds, and that pinnipeds constitute only 8% of the marine vertebrate assemblage from the Purisima Formation at Santa Cruz. To collect a pair of associated dentaries, a tooth, a couple of associated hindlimb bones, and two skeletons (one being articulated) all in one weekend – is surprising, and tripled the number of major pinniped finds I’ve made. I’ll post some updates when some of this material gets prepared.

She nearly got this gull to come to her backpack. Sorry, no pictures of the pinniped excavation.

Fossil Fur seals from Northern California, part 2: The Gilmore Fur Seal

In 1948, Gretchen Burleson published a short article on some fossil pinniped jaws discovered in the Pliocene San Diego Formation, a sandstone mollusk-bearing unit that forms the hills of the San Diego area. These were some of the earliest pinniped fossils to be described from California - previously only a handful had been described, including the strange phocoid Allodesmus from the Sharktooth Hill Bonebed near Bakersfield, California, the woefully incomplete walrus (then assumed to be an otariid) Pliopedia pacifica from the Kettleman Hills, the hopelessly squashed fur seal Pithanotaria from Santa Barbara, and the even stranger Dusignathus santacruzensis from Santa Cruz.

All of these creatures were assumed then to belong to sea lions: most of them were large, and relatively robust, and differed markedly in many respects from true seals. Most of the early descriptions of pinnipeds we now know to be walruses are seemingly obsessed with comparing them to sea lions, and no doubt early workers such as Kellogg were frustrated with the alien nature of many of the fossils: they were about the same size as sea lions, but there were just so many little differences. The answer would not come until much later when decidedly modern researchers like Charles Repenning realized the true walrus affinities of many of these critters (like Pliopedia and Dusignathus).

Unlike the rather large and aberrant jaws of Allodesmus kernensis and Dusignathus santacruzensis, the fossil jaws from San Diego looked like a perfect match for a modern sea lion or fur seal: it had a shallow jaw with small triangular cuspate teeth, and the jaw was rectangular (i.e. the dorsal and ventral margins are parallel). The larger jaws of other better known pinnipeds had too many specialized features to be ancestral to sea lions: Dusignathus had widely flaring jaws without incisors and a canine that projected anteriorly, while Allodesmus lacked cusps on its postcanine teeth, which looked instead like little onions or bulbs. Burleson (1948) assigned these specimens to Pithanotaria, despite the much older age of Pithanotaria starri material described by Kellogg (1922) and the lack of actual morphological characters that identified the jaw of Pithanotaria. Burleson (1948) thought this specimen had a morphology intermediate between Pithanotaria and the modern Northern Fur Seal, Callorhinus.

Skull and dentition of a modern female Callorhinus ursinus, showing

single rooted, cuspate teeth.

In a much later paper by the preeminent paleo-pinnipedologist Charles Repenning and carnivoran researcher Richard Tedford (1977), this specimen was briefly discussed and they concluded that it did not represent Pithanotaria and was likely much closer to Callorhinus ursinus. After observing trends within the dental evolution of walruses like Imagotaria, Repenning and Tedford (1977) had identified the utility of the stage of root fusion as a taxonomic guide. For example, all modern otariids (fur seals and sea lions), the walrus, and some seals have single rooted teeth, while primitive pinnipeds and terrestrial carnivorans retain a number of double and triple-rooted teeth. For whatever reason, these root lobes coalesced through time and resulted in single rooted teeth in a number of taxa.

The dentary of the holotype of Callorhinus gilmorei, from Berta and Demere 1986.

Repenning and Tedford (1977) were surprised that Burleson (1948) had not noticed the interesting configuration of the tooth roots of this specimen: the third and fourth premolars and the molar were still double rooted, while only the first and second premolars were single rooted; in the modern Northern Fur Seal, Callorhinus ursinus, all the lower premolars and molar are single rooted. It was indeed a fur seal, but retained some interesting primitive features.

In 1986, after an extensive excavation of a bonebed in the San Diego Formation that would be christened the Mission Hills Bonebed, additional remains of this fossil pinniped were discovered including several jaws, teeth, skull fragments, and postcranial bones. The discovery of a partial skeleton of an immature female skeleton allowed Annalisa Berta (San Diego State University) and Tom Demere (San Diego Natural History Museum) to describe the San Diego fur seal as a new species - and sure enough, they found that its features placed it as a close relative of the modern Northern Fur Seal, Callorhinus. They named it Callorhinus gilmorei, named after Dr. Raymond Gilmore. In other regards, Callorhinus gilmorei was a relatively small fur seal - substantially smaller than modern skeletal remains, with less strongly developed cusps on postcanine teeth, and a more 'primitive' state of root fusion.

The new specimen of Callorhinus gilmorei from the Rio Dell Formation of Northern California described by Boessenecker (2011)

Subsequently, Kohno and Yanagisawa (1997) reported a tiny partial jaw from the late Pliocene of Japan. This jaw exhibited double rooted cheek teeth (although the anterior premolars were not preserved), and had accessory cusps on the cheek teeth, so they identified it as Callorhinus gilmorei. This extended the range of the Gilmore fur seal to the western Pacific - similar to the range of the modern Callorhinus ursinus.

Needless to say, I had a few ideas to follow once I started looking into Bushell's fur seal specimen. Fossils of C. gilmorei had so far only been found in Middle to Late Pliocene deposits, whereas in the late Miocene and earliest Pliocene of Japan, California, and Mexico the earlier fur seal Thalassoleon occurred (which has all double rooted teeth, and lacks cuspate cheek teeth, among other differences). The new specimen only has one cheek tooth - but it has a well developed accessory cusp, like C. gilmorei, and the first two premolars are both single rooted - also like C. gilmorei. In addition, it is relatively small - many other modern otariids are substantially larger. Furthermore, C. gilmorei appears to be the only middle-late Pliocene otariid in the entire Northeastern Pacific fossil record, which made the identification process somewhat easier.

Next up: Other fossil otariids from California and Oregon, and the Pleistocene Callorhinus
specimen.

References:

Berta, A., and T. A. Demere. 1986. Callorhinus gilmorei n. sp., (Carnivora: Otariidae) from the San Diego Formation (Blancan) and its implications for otariid phylogeny. Transactions of the San Diego Society of Natural History 21:111–126.

Boessenecker, R.W. 2011. New records of the fur seal Callorhinus (Carnivora: Otariidae) from the Plio-Pleistocene Rio Dell Formation of Northern California and comments on otariid dental evolution. Journal of Vertebrate Paleontology 31:2:454-467.

Burleson, G. L. 1948. A Pliocene pinniped from the San Diego Formation of southern California. University of California Publications in Zoology 47:247-254.

Kellogg, R. 1922. Pinnipeds from Miocene and Pleistocene deposits of California. University of California Publications, Bulletin of the Department of Geological Sciences 13:23–123.

Kohno, N., and Y. Yanagisawa. 1997. The first record of the Pliocene Gilmore fur seal in the Western North Pacific Ocean. Bulletin of the National Science Museum, Tokyo 23:119–130.

Repenning, C. A., and R. H. Tedford. 1977. Otarioid seals of the Neogene. US Geological Survey Professional Paper 992:1–87.

Fossil Fur seals from Northern California, part 1: discovery

Earlier this week saw the publication of my third article, concerning fossil fur seals of the genus Callorhinus from the Pliocene and Pleistocene of Humboldt County in Northern California. This paper has been in the works since 2006; I presented a poster on this topic at SVP in 2007. I did some of the initial research in 2006 and 2007, and after my SVP poster, I tried a couple more drafts of the manuscript - but it, along with a couple of other projects, fell by the wayside until I started graduate school. It wasn't until I had the herpetocetine jaw paper off my plate that I returned to this project, and in may of last year I submitted my completed MS to the Journal of Vertebrate Paleontology after three years of intermittent research.

The first page of Boessenecker (2011)

The story really starts in 2004. My buddy Ron Bushell, who helped me identify many of my fossils when I was still in High School, was collecting at a fossil site in Humboldt County, California. At this particular locality, he was looking for large concretions from the Rio Dell Formation which occasionally bear beautiful scallops (Patinopecten) the size of dinner plates, and incredible 6-10" long gastropods.

Ron and his collecting partners walked down the riverbank looking for nodules bearing mollusks, and thought he had hit the jackpot when he found a large nodule, about 2 feet in diameter, just sitting there in the gravel bar. Now, Ron is an experienced nodule collector - he's spent a lot of time collecting nodules with mollusks from the Pliocene and Pleistocene of Humboldt County, and Eocene crabs from Oregon and Washington.

So, if you're a nodule collector, naturally you take out a sledge hammer and attempt to destroy the concretion. Many concretions have nothing in them, and it is better to crack them in the field rather than lug them home and find out later (at some crab localities, Ron knows well enough which concretions will have crabs, and which ones won't, and packs them all out, and cracks them in his garage). Well, he broke this concretion open, and instead of white shells being exposed, familiar (but much rarer) brown fragments flew out onto the river bank - he immediately knew that he had found bone.

Initial preparation of the Bushell specimen.

Normally, Ron would keep any vertebrate fossils from this locality, due to their rarity. However, he also noticed a tooth fragment - and he knew he had found something pretty important. So, just like any crab or mollusk fossil, he collected all the pieces, took them home, and glued them all together in his garage, and begun airscribing the fossil.

Continued preparation of the Bushell specimen.

As it turned out, Ron had found two associated lower jaws (left and right) of a small fur seal, preserved beautifully in relief in a large concretion. He posted these photos on the old "Collecting fossils in California" forum, and I was very interested once I saw it. After a few emails, he offered to let me study the specimen - an opportunity I was most excited for.

Finished preparation of the Bushell specimen.

The Bushell specimen as it was when I first saw it.

The following summer, my fiancee (then girlfriend) and I drove out to California for the summer, but took a detour through Oregon and Humboldt County in order to visit Ron and pick up this beautiful specimen. Thanks to Ron's generosity, this fossil was made available to study - and now (finally, five years later) Ron's wish that it be studied finally culminated in my paper in the Journal of Vertebrate Paleontology.

Next up - introduction to the "Gilmore Fur Seal", Callorhinus gilmorei.

Boessenecker, R.W. 2011. New records of the fur seal Callorhinus (Carnivora: Otariidae) from the Plio-Pleistocene Rio Dell Formation of Northern California and comments on otariid dental evolution. Journal of Vertebrate Paleontology 31:2:454-467

Research featured in the Santa Cruz Sentinel

Hey Folks,

My research with Frank Perry concerning bite marks on fur seal bones was recently highlighted in a recent article in the Santa Cruz Sentinel. Check it out!

http://www.santacruzsentinel.com/ci_17604819

New artwork II: 'rediscovered' specimen drawing

About two months ago, I was cleaning off my desk and found a sheet of vellum paper with an old specimen drawing I had done. This drawing was is of a pair of associated dentaries of the Pliocene fur seal Callorhinus gilmorei. I first presented on this fantastic specimen on my 2007 SVP poster at the Austin, TX meeting.


Unfortunately, I discovered this about three months after my manuscript describing this fossil was accepted in JVP, and there was no way to include it in the published article. To be honest, I could probably do better now, but I think it turned out reasonably well for a journal article figure. In the future I'm going to do a lot more technical illustrations of individual specimens, partly as practice, but also to showcase myself.

Stay tuned! The article will be published in the March 2011 issue of JVP: that's sometime in the next couple of weeks. (Holy god, it's March in only 48 hours!). More artwork is on its way.

Boessenecker, R.W. In Press. New records of the fur seal Callorhinus (Carnivora: Otariidae) from the Plio-Pleistocene Rio Dell Formation of Northern California and comments on otariid dental evolution. Journal of Vertebrate Paleontology 31:2. 14pp.