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.