A bony toothed bird from the Purisima Formation, part 2

After I got the bone identified as a bird, I emailed pictures to my colleague N. Adam Smith, who at the time was a Ph.D. student at University of Texas at Austin, studying with Julia Clarke. We both agreed on the identification of the specimen as a pelagornithid, and also agreed that it could be written up quickly, and we immediately began working on the manuscript. This was the fastest paper I ever wrote - partially because each of us did about 50% of the work, and we went through a bazillion drafts (a new draft every 24-36 hours for four weeks in September and October), and we finally submitted it on Halloween.


We were pretty anal about properly figuring and labeling all the anatomic structures of this specimen in our paper; we were wholly dissatisfied with previous papers which had not labeled the relatively divergent anatomical structures of pelagornithid humeri sufficiently. Many anatomical features are fairly modified relative to non-pelagornithids, and without adequately labeled (or unlabeled) figures, it is difficult for the non-specialist to interpret their morphology; we thought we'd do everyone a favor and do it properly. One exception is Bourdon et al. (2010), who studied Eocene pelagornithids from Morocco (whose paper was also not out yet when we submitted our article).

Figure 2 from our paper, highlighting the anatomical structures of UCMP 219007.

A comparison of humeri of pelagornithids and modern pelecaniform and procellariiform birds. A- Pelagornis sp. (UCMP 219007); B- Pelagornis chilensis, late Miocene, Bahia Inglesa, Chile (holotype, from Mayr and Rubilar-Rogers 2010); C- Pelagornis miocaena, Miocene, France; D- Pelagornis sp., Pisco Formation, Peru (Pliocene); E- Morus bassanus, Gannet, extant (CAS specimen); F- Phoebastria irrorata, Waved Albatross, extant (CAS specimen); G - cf. Macrodontopteryx (synonymized with Dasornis iby Bourdon, 2010), Eocene, Belgium; H- Pelagornis mauretanicus, Pliocene, Morocco.

Many features of pelagornithids (and specifically, Pelagornis spp.) are highly divergent relative to other pelecaniformes (as you can see above, compared with Morus). Additionally, as you can see, our specimen is one of the most well preserved pelagornithid humeri now known, even more so than the beautiful holotype of Pelagornis chilensis, the humerus of which still has quite a bit of matrix encrusted and glued onto the bone, obscuring some of the fossae. One of the pneumatic fossae is actually pneumatized, and bears a pneumatic foramen that appears to connect to the internal cavity of the bone, a condition we had not read about or observed in any fossil or modern relative.

Shaded drawing I made and used for figure 3 of our paper, showing the pneumatic foramen.

Lastly, for our paper I thought I would try a skeletal reconstruction of Pelagornis. It was on my to-do list for the paper, and we already had a couple of drafts sent back and forth when Pelagornis chilensis graced the cover of JVP: it couldn't have been more timely. Although not in the original paper, associated with the press release were several skeletal reconstructions. I emailed the artist Carlos Anzures in Chile to ask for permission to modify it for our study. Well, I didn't just modify it; I redrew it by hand, reposed it, inked the drawing on vellum, and then edited the image in adobe illustrator, to eventually get something like what you see below:

Part of Figure 1 of our paper, showing the skeletal reconstruction of Pelagornis.

Next time: more on pelagornithid evolution and ecology, as well as biogeography and the implications of our find.

Bourdon, E., Amaghzaz, M., and Bouya, Baadi. 2010. Pseudotoothed birds (Aves, Odontopterygiformes) from the Early Tertiary of Morocco. American Museum Novitates 3704:1-71.

Mayr, G., and D. Rubilar-Rogers. 2010. Osteology of a new giant bonytoothed bird from the Miocene of Chile, with a revision of the taxonomy of Neogene Pelagornithidae. Journal of Vertebrate Paleontology 30:1313–1330.

A bony toothed bird from the Purisima Formation, part 1

One foggy morning while doing fieldwork in the Purisima Formation, I spotted a cylindrical bone in the base of a cliff. It initially appeared hollow, but at the time of discovery, I wasn't so sure - sometimes mud and weathering products can obscure certain details of an exposed fossil. Eventually, I decided that it was most likely hollow - I scratched the inside of the bone, and had grains of ancient sand in my palm rather than bone fragments. The first step of excavating a fossil is trying to identify it: if you are positive about A) what bone you have discovered, B) what taxon it belongs to, and C) how it is oriented, you may excavate the fossil in a large block and not damage it. Sometimes you cannot limit your identification to one taxon, and this case was an example.

The end of the bone as it was exposed in the field.

Given the size of the bone, and how common marine mammals are, I assumed the most likely possibility was some sort of a fossil odontocete (toothed whale) jaw: the posterior lower jaws of odontocetes are hollow, and walled with thin bone. The only problem with this identification was that in cross section, odontocete jaws are flattened and sometimes nearly kidney-shaped - while this specimen had a more oval cross section. Nevertheless, it was my best guess at the time. When confronted by a situation like this- where you are uncertain of points A and B above, the best option is to carefully expose as much as possible until you can positively identify it. This is sometimes called "field prepping" (i.e. preparation), and sometimes may result in fragile bits of bones being broken off if you screw up or make a mistake while excavating (because field tools are less precise than lab tools, among other reasons). Aside from potentially resulting in breakage, field prepping takes time - time you may not have, if for example, you are working at low tide within the intertidal zone and have two hours left to finish.

The two sides of the unidentified bone.

Towards the end of the excavation, it was becoming clear that whatever I had found was something strange. I still thought I had an odontocete jaw, and at the time it was my best guess (I'll explain why later). I joked to myself in the field "Perhaps you've found the world's first Pliocene pterosaur!" Little did I know, I was more right about that joke than I realized at the time.

It had a slight curve to it, but it did not fan out at the posterior end like it should have if it were a jaw. I collected it in three big pieces, and upon these coming out, I saw that the sediment inside the bone was cemented - explaining why it was so well preserved, and not crushed. When I began preparing it at home, I was surprised to see that there was no enlarged mandibular foramen - again, a large hole should have been there - but instead, there was no opening in the bone.

A dentary of the bottlenose dolphin Tursiops; the enlarged posterior end and mandibular foramen can be seen on the right side of the picture (from Mead and Fordyce, 2009).

So what the hell was it? Upon leaving the field, I thought all I had was some weird odontocete with a strangely shaped jaw - perhaps a small sperm whale; they often have skinny lower jaws. However, I was once again surprised (and frustrated) by my lack of an identification, now that I had prepared the end of it (whichever end it was!). So I took a guess: some sort of a large bird bone. I did not take my thought too seriously, but the bone was in fact hollow, so I humored myself and opened up my copy of Lee Creek Volume III, and flipped to the article on the Yorktown Fm. bird assemblage.

One side of the complete end of the mystery bone.

The other end of the mystery bone.

Lo and behold, I had a match! The proximal end was a nearly exact match with the proximal fragment of a Pelagornis humerus figured by Olson and Rasmussen (2001); Pelagornis is a gigantic extinct species of bony toothed bird. I couldn't believe it: there was a very specific reason that I had not considered a bird as the owner of the unidentified bone: it was too large to represent any bird already known from the Purisima Formation, even a pelican or an albatross (in fact, it was over twice the size). I did not consider a pelagornithid simply because there are no documented occurrences of pelagornithids in younger than early Late Miocene rocks from the eastern North Pacific: there are plenty of Middle Miocene records of the bird Osteodontornis,

and a couple of records of it from the Monterey Formation. I had always assumed that they had gone extinct in the NE Pacific before the Pliocene; not only that, but this was a late Pliocene fossil. There are some Tortonian stage-like critters from the lowermost Purisima - a possible record of Imagotaria, as well as Megaptera miocaena, a Nannocetus-like cetotheriid, a possible record of Dusisiren, and some odds and ends - but this bird was far, far younger than this assemblage.Comparison of the fossil pelagornithid humerus (A, C) with the fragment from the Pliocene Yorktown Formation of North Carolina figured by Olson and Rasmussen (2001).

Check back for part 2, soon.

References:

Boessenecker, R.W. and N.A. Smith. 2011. Latest Pacific basin record of a bony-toothed bird (Aves, Pelagornithidae) from the Pliocene Purisima Formation of California, U.S.A. Journal of Vertebrate Paleontology 31(3):652-657.

Mead, J. G., and R. E. Fordyce. 2009. The therian skull: a lexicon with emphasis on the odontocetes. Smithsonian Contributions to Zoology 627:1-248.

Olson, S. L., and P. C. Rasmussen. 2001. Miocene and Pliocene birds from
the Lee Creek Mine, North Carolina. Smithsonian Contributions to
Paleobiology 90:233–365.

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

New published article (Part 2): taxonomic problems with Herpetocetus and "cetotheres"

The "cetotheres" have long been a troubled group of fossil baleen whales. Typically, they have throughout there long and confusing taxonomic history been treated as a wastebasket group to include all extinct mysticetes that lack the synapomorphic (i.e. distinguishing) features of the extant groups of baleen whales (gray whales, Eschrichtiidae; rorquals, Balaenopteridae; and right whales, Balaenidae). For a very long time, this group included strange early-diverging mysticetes such as Parietobalaena, Pelocetus, Diorocetus, Aglaocetus (all Miocene mysticetes from the Chesapeake Group of Maryland and Virginia), Cophocetus from Oregon, Cetotherium from the Miocene of the Ukraine, and my favorite mysticete, the problematic Herpetocetus (among others). Many authors during the latter half of the twentieth century doubted that this was a natural grouping, and I suspect that the proliferation of this notion in the literature has more to do with taxonomic laziness on the behalf of mysticete systematists than anything else.

While the taxonomic problems associated with "cetotheres" are a topic for a different post altogether, a brief summary is warranted for the backdrop of the implications in my recently published article. With the advent of cladistics, some studies found that 'cetotheres' are a paraphyletic group of stem-mysticetes (i.e. that they are an unnatural group characterized by primitive rather than derived features). For several years it seemed that the term 'cetothere' should be shit-canned for all eternity, until Bouetel and de Muizon (2006) published a large study on a small Herpetocetus-like 'cetothere' from the Pliocene and latest Miocene of Peru, called Piscobalaena (after the Pisco Formation). They found that some 'cetotheres' form a natural monophyletic group (i.e. a group that is defined on derived features that includes all the descendants of a common ancestor). Because this clade included Cetotherium rathkei, they called this clade the Cetotheriidae sensu stricto, and other 'cetotheres' the cetotheres sensu lato. This same relationship has been supported by several other phylogenetic analyses.

The lectotype jaw of Herpetocetus scaldiensis. From Bouetel and de Muizon, 2006.

Within the true cetotheres, Herpetocetus is the most derived member, and also the youngest surviving member. As previously mentioned, it was based on a lower jaw from the Pliocene of Belgium. When it was described in 1872, a type specimen was never selected, and the lower jaw was selected as a 'lectotype' over thirty years later. The jaw of this animal is pretty distinctive,
Subsequently, many authors have used the distinctive jaw morphology to refer isolated jaws to the genus Herpetocetus. A nearly complete mysticete skeleton from Japan, including a skull, was identified as Herpetocetus due to its jaw morphology. Subsequently, fossils of Herpetocetus have also been reported from the Pliocene and latest Miocene (6-2 Ma) of California, and the early Pliocene (3-5 Ma) of the east coast (North Carolina), basically indicating a 6-2 million year record only in the Northern Hemisphere.

So you can see, when I first thought long and hard about these early Late Miocene (10-12 Ma) Herpetocetus lookalikes, why I was somewhat confused. Herpetocetus also has distinctive earbones and skulls (based on specimens associated with jaws), and there aren't any earbones or skulls with the typical "Herpetocetus morphology" that occur any older than 6 Ma (there is one undescribed skull from the 6.8 Ma Santa Cruz Mudstone I've identified as Herpetocetus aff. bramblei). What is known from the 10-12 Ma Santa Margarita Sandstone, in addition to the jaws in question, is Nannocetus eremus.

The holotype braincase of Nannocetus and a quick and dirty reconstruction based on the rostrum of Herpetocetus sendaicus.

Nannocetus is a really tiny (greatest width across the skull is about 10 inches) weird mysticete, originally described in 1929 by Remington Kellogg. A second specimen from the Santa Margarita Sandstone was described by Whitmore and Barnes (2008), and is the only other known 'true cetothere' from the Santa Margarita. However, Nannocetus is not yet known by a jaw; could Nannocetus be the rightful owner of the two dentaries I described?

If so, then the supposedly distinctive anatomy of the lower jaw of Herpetocetus is not distinctive, and raises important questions about referring isolated dentaries based on their morphology. Additionally, this problem raises an even more important issue: what, then, of fossil baleen whales described solely based on isolated lower jaws? Most of them are probably invalid, because lower jaws *might* only be diagnostic at the supraspecific level (i.e. at the level of a genus or subfamily - whatever the hell those are). "But Bobby, the type species of Herpetocetus is based only on a lower jaw!" Aw, crap. That's right. We've now come full circle: Herpetocetus may or may not be a valid name in the first place, if jaw morphology is insufficient for taxonomic purposes.

Before us mysticete taxonomists go off ready to sink Herpetocetus as a nomen dubium, there are a few important things I pointed out in the article which should be remembered: 1) The fossil dentaries DO show a couple of features distinct from Herpetocetus, including a mandibular foramen with a a lanceolate opening, unlike Herpetocetus. 2) Although highly likely, it is possible that these dentaries are not Nannocetus. However the age discrepancy does mean something in and of itself. 3) Distinctive skull fragments showing some synapomorphies of Herpetocetus were also in the "type series" described in 1872, so it is unfair to say that it was based only on a lower jaw.

With those exceptions in mind, I hope my new article has established some caveats for mysticete workers. Additionally, this work has identified the possibility that mysticete jaws are perhaps diagnostic to the generic level; this still means they are unsuitable as holotypes, but that they are by no means useless - the jaws of mysticetes tell us quite a bit about the animal's feeding and its relationships (although they are not as fine-tuned as, say, parts of the skull). Hopefully future fossil mysticete holotypes will be designated only on material that is really diagnostic, and hopefully will include comparable elements like earbones, braincases, and (also hopefully) the posterior end of the lower jaw.

Boessenecker & Perry 2011 is the featured Palaios article for March 2011

Last night, after a delicious dinner at one the best steakhouses in Montana, I returned to my apartment to find an email from the editors of Palaios. They both nominated my recent article "MAMMALIAN BITE MARKS ON JUVENILE FUR SEAL BONES FROM THE LATE NEOGENE PURISIMA FORMATION OF CENTRAL CALIFORNIA" to be the featured Palaios article for March of this year.

What does that mean exactly? First and foremost, that means my article is now open access, and freely available (to everyone) here (click here for the pdf). So, download the article while you still can access it! You have 30 days. Secondly, it means that I totally kick ass.

You can see the list of featured articles (including mine) here. Not only is my article right up at the top, but it's also one of the only ones in all caps. Too bad they couldn't put in bold, italics, and make it flash different colors while they were at it.

NOTE: Many of these links may not work past the end of March.

New published article (Part 1): herpetocetine jaws, and an example of finding a "simple" research project

The new issue of PaleoBios, the paleontology journal published by UCMP at UC Berkeley, includes my new article on herpetocetine jaws from the Santa Margarita Sandstone in central California. During the fall of 2008, I was in my first semester of graduate school, and was taking a difficult, time-intensive course on advanced stratigraphy. At the time, I already had two articles I had been working on: one on my undergraduate research concerning a new fossil vertebrate assemblage from the Purisima Formation, and another on Plio-Pleistocene fur seals from the Wildcat Group in northern California (both are currently in press). However, neither was in any shape to be published anytime soon - one was only half written, and the one that was nearly finished needed a lot of work (i.e. quality control). I needed a new manuscript to work on, to give me something to do that semester aside from stratigraphy, which had started to eat away at my brain. In other words, I needed to start something fresh from scratch, with a clear beginning, a clear end, and a clear message.

The right dentary of UCMP 85431. Scale bar =10cm. From Boessenecker (2011).

A month earlier, I had given a presentation (coauthored with Jonathan Geisler) on a new skull of Herpetocetus bramblei I had collected from the Purisima Formation in 2007. While ruminating on possible projects, I suddenly remembered a partial lower jaw from the Santa Margarita Sandstone that looks a lot like the lower jaw of Herpetocetus*. The problem is, the Santa Margarita Sandstone is early Late Miocene in age (10-12 Ma), while the oldest known bona fide specimens of Herpetocetus are latest Miocene to earliest Pliocene in age (~5 Ma). In fact, the oldest known described specimen is the fragmentary type specimen of H. bramblei, which is right about 5.33 Ma. So, this specimen (UCMP 85429) is MUCH older than any known specimen of a "true" Herpetocetus.

*All species of Herpetocetus have relatively similar lower jaws, and currently the lower jaw has only been described for the type species, Herpetocetus scaldiensis (the type specimen of which is a lower jaw - more on this later).

The left dentary of UCMP 85429; scale bar = 10cm. From Boessenecker (2011).

The lower jaw of baleen whales has long been assumed to be a fairly diagnostic element, at least in certain groups. Herpetocetus scaldiensis certainly has a very distinctive mandible. Other fossil mysticetes certainly have distinctive mandibles as well. Many fossil mysticetes (H. scaldiensis, Balaenoptera davidsonii, Archaeschrictius ruggieroi, etc.) have been described just off of their lower jaws. Are dentaries really that diagnostic? Perhaps. Demere (1986) used mandibular features to reevaluate "Eschrichtius davidsonii" from the San Diego Formation, which was a chunk of a 30% complete mandible, missing the anterior and posterior ends. Being able to refer a new dentary to this taxon, he demonstrated that the "davidsonii" morphotype was actually a rorqual, and assignable to the genus Balaenoptera, which led to its recombination as Balaenoptera davidsonii. Clearly, mandibular morphology is important, and can be used to assess the taxonomy of certain groups, and 'fix' the taxonomy of certain problem taxa. Are these specimens the oldest known records of Herpetocetus?

Reconstructed lower jaw of Herpetocetinae genus and species indet., based on UCMP 85429 and 85431. From Boessenecker (2011).

Reflecting upon the known fossil record of "true cetotheres" - relatives of Cetotherium and Herpetocetus (an entire other topic worthy of its own post) - I was able to formulate some interesting questions I could ask (and attempt to answer), which would make a nice core of an article. With these objectives in mind, I started taking copious notes on the anatomy of the fossil specimens, and eventually typed these notes up into an anatomical description for the article. By the end of the semester, I had a manuscript that was about three-quarters finished. During spring 2009, I wrapped up the discussion, and constructed some figures. I had a few people look at it and make some comments. Morgan Churchill looked at it late in spring, and had some of the most constructive and useful edits. That summer, I TA'd the Geology Field Course for MSU, and during some of the weeks, I took my manuscript out into the field with me, along with a red pen. In between helping students, I sat out in the hot sun, and critically examined every sentence in the manuscript. I even drafted one of the figures (on vellum, with nice pens) around the campfire one night after a few beers. By the end of the second to last project at field camp, I had all my edits finished, and I sent it off to PaleoBios for review.



To be continued...

Boessenecker, R.W. 2011. Herpetocetine (Cetacea:Mysticeti) dentaries from the Upper Miocene Santa Margarita Sandstone of Central California. PaleoBios 30:1:1-12.

Deméré, T.A. 1986. The fossil whale, Balaenoptera davidsonii (Cope 1872), with a review of other Neogene species of Balaenoptera (Cetacea: Mysticeti). Marine Mammal Science 2:277–298.