Recent fieldwork in the Purisima Formation, Part 2: a possible new species of Herpetocetus?

Back in late May, Dick Hilton (Sierra College) and I did a three day field trip collecting fossil vertebrates from a locality in the Purisima Formation I recently got a permit for. On the second day, excavated a large block of sediment with what I assumed at the time were sirenian bones. I had not seen the bones except in cross section, and because they were somewhat dense, I thought they might be from a sea cow. We quickly carved out a large block, and due to the cohesive nature of the sediment, we were able to wrap it in tinfoil and duct tape. It was one of the first finds of the day, and I thought there could definitely be something neat inside. Because we were only a half mile from the cars, I left my pack with Dick and hoofed it back to the car with the thirty pound block, and also to grab some gatorade I had left in my car. When I returned, Dick was taking a siesta, and after some lunch, we headed further down the beach. Only a few hundred feet down I spotted a distinctly potato-shaped thing sticking out next to a piece of bone: it rather looked to me like a tympanic bulla, and I climbed up a bit to check it out. It was in fact a tympanic, and when the rest of the piece came out, I was able to see that it was in fact a nearly complete squamosal, complete with the bulla and posterior process of the petrosal. Dick and I thought the trip had been a success just because of this specimen, especially because it was from a section of cliffs where neither of us expected to find anything.

Dick Hilton digging up a huge baleen whale tympanic.

I couldn't have been more wrong. Unfortunately, I didn't know that I was until after the SATLW (Aquatic Tetrapods) conference. I did have a day or two before the conference to prepare the squamosal, and it did indeed have a plug-shaped posterior process of the petrosal, indicating it belonged to the Herpetocetinae, which includes Herpetocetus, Nannocetus, (probably) Piscobalaena, and Cephalotropis (according to Steeman, 2007). After the conference, I opened up the duct taped jacket and began preparation. After a couple hours the exposed pieces were still not making sense, and then I found a couple of bones that looked like they were adjacent to one another. When I removed them, there was a tiny neck of bone connecting them – and after a little more preparation, I realized it was a Herpetocetus petrosal and posterior process. Damnit, another goddamn Herpetocetus.

The petrosal and posterior process of the new specimen, with the facial nerve canal labeled. Upper left is ventral, lower left is dorsal, and right is medial view.

The skull with (partially incorrectly) articulated petrosal of the new skull in dorsal (top) and ventral (bottom) views.

Once I had enough of the block prepared, I realized I had quite a bit of the ventral portion of a small braincase preserved. It includes both exoccipitals, one occipital condyle, the basioccipital, the right squamosal, and the complete petrosal. After preparation, the petrosal is most similar to petrosals of Herpetocetus. This may be a bit technical, but herpetocetine baleen whales have several peculiar features that define them as a group. The posterior process of the petrosal – which is typically an elongate strap of bone that connects with the skull posteriorly – is very short and plug-shaped in these animals. Additionally, the posterior process (which is rarely found attached in isolated fossil mysticete petrosals) is flat and contributes to the lateral side of the skull, instead of being 'hidden' in a trench between the squamosal and exoccipital bones. Secondly, some herpetocetines have a flattened anterior process that is blade shaped; this structure is typically conical and robust or knoblike in most other mysticetes. Clearly, this specimen exhibits both of these features. Additionally, Herpetocetus spp. exhibit a large triangular flange on the side of the bone, which overhangs the squamosal – also present in this specimen. Additionally, herpetocetines all have extremely small earbones relative to most mysticetes. Unfortunately, the neck of the posterior process appears to have been deformed slightly, and when the main portion is articulated correctly, the posterior process sits in its trough a little wonky, and when the posterior process is articulated correctly, the main portion doesn't articulate well.

The posterior process, squamosal, and tympanic of Herpetocetus bramblei.

The two alternate articulations of the petrosal showing correct articulation of the posterior process (left) and correct articulation of the body of the petrosal (right).

The temporal region of the skull of Herpetocetus bramblei with the petrosal outlined in red.

However – it shows several features that differentiate it from all species of Herpetocetus as well as other herpetocetines like Nannocetus and Piscobalaena. Firstly, the anterior process is medially oriented – it is usually anteriorly facing instead. Second, the posterior process is very transversely narrow and elongate – it is typically more nearly circular in other species. Lastly, the most bizarre feature is that it has a very long anterior fissure of the facial nerve canal which is contorted into an S-shape – something I have not seen in any mysticete, fossil or modern.

Various mysticete petrosals in ventral view, showing two fossil rorquals (Plesiobalaenoptera and Balaenoptera sursiplana), a modern balaenid (Eubalaena japonica), the new specimen, and two other Herpetocetus specimens.

This is pretty exciting, and I am looking forward to preparing the other specimen, which includes part of a squamosal and a tympanic, and most likely a petrosal. It should not be too difficult to get these specimens written up and described.

Further Reading

Geisler, J. H. & Luo, Z.-X. 1996. The petrosal and inner ear of Herpetocetus sp. (Mammalia: Cetacea) and their implications for the phylogeny and hearing of archaic mysticetes. Journal of Vertebrate Paleontology, 70, 1045–1066.

Steeman, M.E. 2007. Cladistic analysis and a revised classification of fossil and recent mysticetes. Zoological Journal of the Linnean Society 150:875–894.

Steeman, M.E. 2010. The extinct baleen whale fauna from the Miocene-Pliocene of Belgium and the diagnostic cetacean ear bones. Journal of Systematic Palaeontology 8:63-80.

Whitmore, F.C., and L.G. Barnes. 2008. The Herpetocetinae, a new subfamily of extinct baleen whales (Mammalia, Cetacea, Cetotheriidae). In C.E. Ray, D.J. Bohaska, I.A. Koretsky, L.W. Ward, and L.G. Barnes (eds.). Geology and Paleontology of the Lee Creek Mine, North Carolina, IV. Virginia Museum of Natural History Special Publication 14:141–180.

Recent fieldwork in the Purisima Formation, Part 1: Gigantor whale jaw

If you pay attention to paleo-related news on the intertubes, you may have seen a recent article about a 700 lb dinosaur bone excavated from the Morrison Formation near Fruita, Colorado. Fellow MSU student Krista Brundridge was even interviewed and involved in the excavation. They only state that the bone is from the animal's back, so I can only assume that it's a huge sauropod vertebra. Which means that maybe the kind folks over at SV-POW! will be drooling over the news. If people really wanted to dig up humongously sized plaster jackets, they'd come to California and dig up whales. Why, back in may, Dick Hilton and I prospected a locality in the Purisima that hasn't been collected by paleontologists in over twenty years, and over the course of two days, found dozens of multi-ton blocks just sitting there on the beach. Many of them had vertebrae (which unlike those of sauropods, are much more conservative in their anatomy), ribs, and other odds and ends. However, I counted many that had skulls. One block that was the size of a pickup truck had a complete skull, at least one lower jaw, and apparently part of an articulated vertebral column and ribcage.

Me posing with half of a gigantic whale jaw.

Wait a second, you say. Dinosaur paleontologists scrounge up every scrap of bone, and re-re-describe old fossils (i.e. Dryptosaurus was first described, then re-described, and then re-re-described), and bitch and moan about there not being enough material for new researchers. How would complete skulls of baleen whales just sit on the beach without some intrepid explorer to come along and excavate or collect them? Below, I've got a photo of what used to be a complete baleen whale jaw sitting in a large boulder, ~20 feet above the beach. I climbed up to it, which was pretty hairy – usually the Purisima Formation is sandstone, and easy to carve handholds in, but this was nasty hard fractured mudrock. This jaw must be in a concretion that weighs the same as my small Honda. For baleen whales, jaws are "relatively" diagnostic (see here, here, and Boessenecker 2011), so specimens like this are of interest. Baleen whale skulls are of course diagnostic, and it is unfortunate that they are languishing like this.

It was kind of a pain to get down from there.

One problem, you might say, is that they're big, and in very tough rock. Yes, I spent five years of my life (intermittently) preparing a mysticete skull in a concretion that I collected from the Purisima Formation. Sure, it's a big heavy skull, but surely smaller and less heavy than any ceratopsid skull you can point at. Obviously, blue whales have bigger crania than dinosaurs like Triceratops. Most fossil mysticetes have skulls that are smaller than or roughly the same length as the largest "Torosaurus" skulls, but many museums out there don't hesitate to go dig up more Triceratops skulls. Is it the often concretionary matrix and the time-intensive nature of the preparation that makes whale fossils "unpopular"? I don't think so, because I can't count the number of dinosaur bones (even undiagnostic material like ribs) encased in hard rock being prepared.

Permanently borrowed from SV-POW! Thanks guys, this image is awesome.

Are whales and whale fossils just unpopular within vertebrate paleontology? Maybe. Given how whales captivate the imagination – mind you, not in the gory, Velociraptor-chasing-kids-through-a-kitchen and lawyer-eating sort of way but the holy-shit-its-a-brachiosaurus-on-a-grassy-hill sort of way – I highly doubt that cetaceans lack the cool-factor. They may not have big sharp pointy teeth... oh shit, I forgot that fossil sperm whales are far more impressive than any puny theropod. Sorry, Livyatan beats T. rex. I think the real problem is that we have the Jurassic Park generation in vertebrate paloentology now – and not to sound like a bitchy hipster, although I am of the correct age group – I was into paleontology before Jurassic Park came out.

Nevermind that in the background.

Perhaps this is a problem that is, within the United States, unique to Northern and Central California. Southern California fossil cetaceans are really well taken care of, and get excavated and pampered at places like LACM, the Cooper Center, and the San Diego Natural History Museum. The extremely rich Calvert Cliffs and other Mio-Pliocene units of the Chesapeake Group of the mid Atlantic coastal plain are covered by the Calvert Marine Museum, the Smithsonian, and my dear friend Butch Dooley at the Virginia Museum of Natural History. Florida fossils are generally covered by the FLMNH and the University of Florida. The comparatively rich fossil record in the Oligocene and Miocene of Washington State (and parts of Oregon as well) are covered by the Burke Museum in Seattle. However, all of the UCMP students who collected a ton of material from Northern California in the 1970's and early 1980's moved on elsewhere.

I don't mean to complain – having a surplus of fossils available for my research is nothing to complain about. However, it is depressing if not distressing to see so many fossils I could not collect, prepare, and study alone in five or six lifetimes, just sitting out there on the beach. So: to all of you dinosaur folks who feel perhaps the field is a little too crowded, too much of a circlejerk, or whatever, come join marine mammal paleontology! Trust me, there are is a large hoard of new genera and species out there just waiting for the taxonomically hungry. In five years of serious collecting, I've got enough material to research for another ten years, and this is barely scraping the surface. So, this is a call for action! If you're interested in marine mammal paleontology, go dig up a whale (instead of Apatosaurus #32, or NewGenusOfUninterestingChineseDinoBird #54, or re-re-redescribing something everyone is already familiar with) or find someone who can help you (...or me, for that matter).

Unfortunately, the sad reality is that that jaw I posted above will probably not be collected. I don't have the funding, resources, or the connections (read: friends with heavy machinery) to collect stuff like that now. To be honest, it isn't complete enough for it to be worth it anyway. But that's besides the point: it was at one point, and another one will come along that will be worth collecting. Will we be up to the challenge?

Sorry for the rambling here, the rest of these posts will be about fieldwork I did with Dick Hilton in May, I promise!

More problems with Herpetocetus

Back in June at the Aquatic Tetrapods conference I coauthored a poster with Joe El Adli (San Diego Natural History Museum) and Jonathan Geisler (New York College of Osteopathic Medicine) on some of the taxonomic problems of Herpetocetus. Herpetocetus, as I've mentioned before, is an enigmatic small bodied mysticete whale which many bizarre and derived features, while retaining some primitive features as well. Fossils of Herpetocetus are fairly common in Northern California, particularly in the Purisima Formation - or maybe I just have a knack for finding them. Thus far, there is only one described species of Herpetocetus from California: Herpetocetus bramblei, named by Whitmore and Barnes (2008) from a very partial skull (basically just a squamosal with part of the exoccipital, parietal, and pterygoid) with a petrosal from the Purisima Formation. In summer 2007, I excavated a nearly complete skull of this same species from near the type locality, and last summer, I excavated a second specimen which lacked the braincase but included a complete rostrum. Since this topotypic material was collected, additional specimens from other localities in the Purisima Formation indicate that two additional undescribed species are present - one of the new species was discovered very recently, and I'll have more on that soon.

*Holotype, for the non-specialist, is the specimen which a new species is based off of. It should be representative of the new species in terms of its anatomy, and should be relatively complete enough to be comparable to other taxa. A type locality is where the holotype specimen originated.

There are several other described species of Herpetocetus from other corners of the globe - all from the Northern Hemisphere. The genus was first described from the Pliocene of Belgium (Herpetocetus scaldiensis) based on a partial dentary. A partial skull from the Pliocene Yorktown Formation was described as Herpetocetus transatlanticus, also by Whitmore and Barnes (2008). In the 1960's, an isolated tympanic bulla from Japan was named as the type specimen of Mitzuhoptera sendaicus, and a fossil mysticete skeleton with a skull, earbones, and dentary shared both the dentary morphology of Herpetocetus scaldiensis as well as the tympanic morphology of Mitzuhoptera sendaicus, and Oishi and Hasegawa (1995) transferred M. sendaicus to Herpetocetus, resulting in the new combination, Herpetocetus sendaicus. Each of these records is from either side of the Pacific (east and west) and the Atlantic (east and west).

How diagnostic are bullae and dentaries? I've already addressed problems with the jaw morphology of herpetocetines (here and here), and mysticetes in general. If you recall, there are two problems concerning the dentary of Herpetocetus spp. in particular: 1) The dentary of the possible sister taxon Nannocetus is not yet known, and dentaries substantially older than Herpetocetus (and possibly belonging to Nannocetus) are nearly identical to Herpetocetus (see below image), indicating that this general morphology is possibly characteristic of a larger group of whales. 2) Some species of Herpetocetus have dentaries that are very difficult to tell apart and lack autapomorphic characters (unique derived features), and thus are not suitable as holotypes. This logically results in the implication that Herpetocetus scaldiensis, which is based on a jaw, is the type species of Herpetocetus, and thus the species and genus may be taxonomically invalid or nomina dubia (means dubious name in latin).

The first figure of our poster, showing comparative drawings of various fossil herpetocetines.

Earbones have long been used for taxonomic purposes, and in many cases have been designated as holotypes. Sir Richard Owen designated many isolated bullae from the Plio-Pleistocene Red Crag of eastern England as holotypes (all of which have been sunk; e.g. Balaena definata). It is unclear how diagnostic earbones are for baleen whales: petrosals (otherwise known as periotics - the inner ear bone) have all sorts holes and knobs and crests and are rather easy to tell apart from genus to genus. A recent paper published by Eric Ekdale, Annalisa Berta, and Tom Demere (2011) indicate that earbones of extant mysticetes are diagnostic to the species and are easily told apart. Additionally, Steeman (2010) reexamined a large suite of earbones previously described by taxonomic mad man P.J. Van Beneden, who is largely responsible for constipating the entire field of mysticete systematics for over 100 years. Steeman (2010) found that many of these earbones - specifically petrosals - may be diagnostic tools, and generally reached a similar conclusion like Ekdale et al. (2011). But what about bullae?

The second figure from our poster, showing variation in tympanic bulla morphology from various herpetocetines. Note the overall similarity between Herpetocetus spp.

Bullae of three species of Herpetocetus have been described: H. scaldiensis, H. transatlanticus, and H. sendaicus. In our poster, we figured all known bullae (described or undescribed), including both the holotype of Mizuhoptera sendaicus and the referred specimen of Herpetocetus sendaicus, and a new bulla of Herpetocetus bramblei. Additionally figured are bullae of Nannocetus and Piscobalaena, also herpetocetines. We concluded, as we hope that you will when looking at this figure, that the bullae of different Herpetocetus species do not vary significantly from species to species. They are, on the other hand, diagnostic at the family level: they are clearly distinct from all other bullae of (described) cetotheriids. However, a bulla that is only distinct at the genus level is inadequate to be used as a holotype. This suggests that Mizuhoptera sendaicus, unsurprisingly, is probably a nomen dubium. It also indicates something interesting is going on with the skulls of mysticetes, or at least cetotheriids: tympanics are slightly less informative than the petrosals. It might be possible someday to quantify how phylogenetically useful different anatomical regions are, aside from just counting up the number of characters used per anatomic region in a cladistic analysis. Who knows, maybe someone has already thought of that and developed a method.

Further Reading:

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

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

References:

El Adli, J., Boessenecker, R.W., and J. H. Geisler. 2011. Taxonomic problems of and relationships among species of the fossil baleen whale genus Herpetocetus. Sixth Triennial Conference on Secondary Adaptation of Tetrapods to Life in Water Program with Abstracts: 23.

Ekdale, E.G., A. Berta, and T.A. Demere. 2011. The comparative osteology of the petrotympanic complex (ear region) of extant baleen whales (Cetacea: Mysticeti). PLOS One 6:1-42.

Oishi, M., and Y. Hasegawa 1995. Diversity of Pliocene mysticetes from eastern Japan. The Island Arc 3:436–552.

Steeman, M.E. 2010. The extinct baleen whale fauna from the Miocene-Pliocene of Belgium and the diagnostic cetacean ear bones. Journal of Systematic Palaeontology 8:1:63-80.

Whitmore, F.C., and L.G. Barnes. 2008. The Herpetocetinae, a new subfamily of extinct baleen whales (Mammalia, Cetacea, Cetotheriidae). In C.E. Ray, D.J. Bohaska, I.A. Koretsky, L.W. Ward, and L.G. Barnes (eds.). Geology and Paleontology of the Lee Creek Mine, North Carolina, IV. Virginia Museum of Natural History Special Publication 14:141–180.