Saturday, November 21, 2009

Away For Thanksgiving

Sorry about the lack of posts over the last week or so; in a few hours I will be flying to California for Thanksgiving break, and this time will have 8 days (and thus, another 10 days before I write on here again) - my longest Thanksgiving ever, I think. What's this mean for me? Well, obviously I'm going to eat a lot of turkey with some of my relatives (my favorite set of cousins will be there; awesome). However, Thanksgiving is the first iteration of my 'real' field season.

Every spring, all my friends get antsy and extremely excited for the summer field season with Museum of the Rockies; they spend about two or more months digging up dinosaurs in the badlands of Montana - usually the Judith River Formation and the Hell Creek Formation, and formerly the Two Medicine Formation (although a few camps have been there within the last few years).

Summer has a completely different meaning for me; there is very little erosion on the coast, and summer is typically a season of crowded beaches, traffic over highway 92 and 17, high school kids are out of class and go smoke pot on the beach (and usually sit right on the outcrop, and are too dumb to move). Beach sands typically accumulate during the summer, piling up ever higher, foiling any attempt at collecting material below the high tide line. The lack of rain and storm waves means that most exposures by now are coated with a healthy coat of dust and grime, rendering any possibility of spotting smaller shark teeth and bird bones improbable.

Winter, on the other hand, is my field season, albeit short. Winter storms clean the cliffs off, erode the cliffs, and strip sand off beaches, allowing collecting from the wave-cut platform and the base of the cliffs (sand movement during storm and fairweather usually abrades the portions of cliffs that are buried during the summer as well). Additionally, the cold temperatures drive away the throngs of people who flock to the boardwalk and Santa Cruz beach during the summer, which means all I have to deal with is rush hour traffic.

Winter obviously has its drawbacks; 1), it's cold; 2), it's rainy; 3) the hours are short; and 4), the reduced sand level (sand gets stored in offshore sand bars during the winter months) often means access to certain areas is much trickier, often requiring some creativity and flexibility (i.e. lots of climbing, boulder hopping, etc.). This winter is an El Nino event, which excites the hell out of me - some vicious winter storms this year would be awesome. Last winter was fairly lame (although the little rain we did receive made it easy to get out), although I did pick up a nice delphinoid odontocete skull and a partial Herpetocetus dentary. Winter 2007-8 was just amazing, however; a nearly complete Carcharocles megalodon tooth (the day before christmas, no less!), only the second known for the Purisima (and only one available to scientists for research - will be donated to UCMP in the next few months), as well as a 40-50% complete female fur seal skeleton, a juvenile Herpetocetus dentary, and a smattering of pinniped bones.

I wish I really could properly convey my excitement to you - Thanksgiving field trips are the prelude to the really good 'stuff', so to speak, although storms typically haven't cleaned the cliffs and lowered sand levels enough to be terribly different from summertime. However, the three months between summer and thanksgiving makes it seem that much more prolific. I'm also uber excited, because I will be visiting some old localities I haven't been to in a while.

On a final note, for the last three and a half years I've been working on a manuscript version of my undergraduate research project, which was the description and analysis of a new, probable late Pliocene assemblage in the Purisima Formation. In 2007 I sent a copy of this to a couple colleagues of mine (Frank Perry, Santa Cruz Museum of NH, and Chuck Powell, Menlo Park USGS); unfortunately, my writing skills were relatively poor at the time, the manuscript was incomplete, figureless, and had older 'chunks' from previous drafts embedded, much like an accreted terrane that is then subjected to regional metamorphism; a really ugly, foul smelling, nasty thing that no one should bother looking at (can't you tell I enjoyed metamorphic petrology?!).

Needless to say, after reading the revisions, I felt pretty guilty that I had bothered having them proofread it in the first place. In any event, I've spent the last month seriously reconsidering every word in the manuscript, and rewriting it piece-by-piece into a coherent piece of literature, complete with submission-ready figures; last night, I emailed it out (again), and hopefully this time there will be less 'red'. I showed up at our local sports bar (Spectators, my third home; second home being my apartment, first home being my office) and let the 60-page paper drop to the bar table with a resounding 'thud', which, oddly enough, drew applause from my (drunk) friends and a high five from my friend (Hi Christina!) who's going to proofread that copy. Within seconds, a red pen was already out, which had crossed out my last name and replaced it with "boogernecker". Thanks, guys.

Anyway - Happy Thanksgiving!

Tuesday, November 10, 2009

New artwork - skull drawings

Well, folks, I've been a little busy recently, but in the last month or so I've gotten back into artwork in a big way; every once in a while I'll do a drawing I don't like, and I won't draw for a long time. This first drawing was formerly one that I got bored with a couple years ago. Then, after teaching a lecture on scientific illustration, I saw the bare bones shading I had done, and all of a sudden Dorudon started cackling and laughing at me; I took it as a challenge. I worked nonstop for about 10 hours, and finished it up at 3 in the morning that night. I started this thing in 2007.
Cranial drawing of the archaeocete whale Dorudon atrox,
from the Eocene of Egypt. 2d, graphite, 2007-2009.

The next drawing I completely forgot about; this is a drawing of a walrus (Odobenus rosmarus) cranium on display at the Smithsonian. This was shaded waaay too much, but the particular style of drawing I developed in high school called for really dramatic contrast and lights and darks, so that's what I'm stuck with.

Cranial drawing of modern walrus, Odobenus rosmarus. 2d, graphite, 2007.

The next drawing is actually pretty big; I finished this one on sunday. This is a lateral view of a 7-9' long (can't remember exactly) Sei Whale (Balaenoptera borealis) cranium on display at the UC Museum of Vertebrate Zoology in Berkeley. The drawing is nearly 2' wide.

Cranial drawing of a Sei Whale, Balaenoptera borealis. 2d, graphite, 2009.

The last drawing took a couple days; this one's of a pretty gnarly critter - the skull of Otaria flavescens, the Southern Sea Lion. The skulls of this animal have all sorts of grotesque knobs and protrusions. This individual wasn't too bad, but note the projections on the dorsal braincase posterior to the orbits.
Cranial drawing of Otaria flavescens, the Southern Sea Lion. 2d, graphite, 2009.

So - if you need scientific illustrations for a publication, or would like to commission something, keep me in mind...

Sunday, November 8, 2009

Reconstructing a fossil walrus, part 2: the finished product

So, quick rehash of part 1, in case you're really that lazy. To reconstruct the cranium and jaws of Dusignathus santacruzensis (which has an 'exploded' holotype cranium with isolated parts that don't quite match up well), I used more complete material of a younger species, Dusignathus seftoni, from the late Pliocene San Diego Formation. I used the skull of D. seftoni as a template to 'hang' the various parts of D. santacruzensis on to.
Cranial mosaic of Dusignathus seftoni with holotypic fragments of Dusignathus santacruzensis 'hung on'.

From here, it was pretty much an exercise in printing it off, tracing it, and inking it out (followed of course by scanning and some image editing). Below is the finished product.

New cranial restoration of Dusignathus santacruzensis.

Cranial restoration of Mitchell (1975).

Compare this with the older cranial restoration of Dusignathus santacruzensis by Mitchell (1975); there are some obvious differences, including a significantly smaller orbit, and a dorsoventrally shallower cranium, which serves to make the dentary appear much more massive.

Cranial reconstruction of Dusignathus santacruzensis with photos of crania
Dusignathus seftoni and Gomphotaria pugnax. Not to scale.

So... that's basically that. During my lifetime, I want to test this hypothesis of what this animal looked like by finding a new cranium of D. santacruzensis; this won't be easy, and will probably take a lot more searching (i.e. decades). Wishful thinking, I know... Otherwise, I hope that this gives you folks some ideas on how to tackle similar problems with incomplete material you may be studying.

Mitchell, E.D., jr. 1975. Parallelism and convergence in the evolution of the otariidae and phocidae. In Biology of the Seal, p. 12-26.

Monday, November 2, 2009

New lower jaw of the extinct lipotid Parapontoporia

Before I dive back into fossil odobenids, I'd like to show off something I just finished preparing. I collected this specimen from underwater in July in Santa Cruz County; I arrived at the exposure several days after I initially discovered it and coated it with vinac. Unfortunately, upon my return when I intended to collect it, the tide wasn't low enough; the specimen was exposed on the apron of a cliff, and was about 6" underwater. Unfortunately, I was there at low tide, and in the intervening days, the sand on the beach had locally eroded, allowing waves to go *just* a bit higher on this 5m stretch of beach.

Oblique view of the lower jaw of Parapontoporia wilsoni.

Anyway, after forty minutes of carving out a pedestal, cursing like mad because I thought I was going to destroy the fossil, and being investigated (and probably secretly laughed at) by a sea otter and a sea lion, I decided to undercut the pedestal. The pedestal was about 14" long and 5" wide, and I was worried that it might crack in half during undercutting - any bone exposed in that crack might fall out (and be swept away by the surf), and then I wouldn't be able to connect the bone from the two pieces of the pedestal back together. Needless to say I was shocked (and endlessly pleased) when the pedestal popped off perfectly.

Dorsal aspect of the fused dentaries of Parapontoporia wilsoni.

Lateral aspect of the fused dentaries of Parapontoporia wilsoni.

Parapontoporia is a very conspicuous member of late Neogene marine vertebrate assemblages in California and Baja California, and has also been reported from Japan. In California, it is known from late Miocene (Tortonian - 9 Ma) through late Pliocene (Piacenzian - 2 Ma) strata, including the San Mateo, San Diego, Capistrano, Pismo , Purisima , and Wilson Grove Formations. Three species are known - Parapontoporia pacifica from the late Miocene Almejas Formation of Baja (Barnes, 1984), Parapontoporia wilsoni from the Mio-Pliocene Purisima Formation (Barnes, 1985), and Parapontoporia sternbergi from the San Diego Formation (Barnes, 1985).

The cranium and jaws of Parapontoporia sternbergi, on display at the San Diego Natural History Museum.
Since description, P. pacifica is still only known from one partial cranium, while P. sternbergi is now represented by about a dozen well preserved crania, and several nearly complete lower jaws. While only the partial holotypic cranium of Parapontoporia wilsoni has been described, however, there are now probably around two dozen crania known, in addition to around 50-75 periotics. Only two lower jaws are known, though - one crappy fragment at UCMP, and a neat (but highly abraded) fragment of an articulated rostrum with teeth at CAS. Two more well preserved jaws are known, both from the early Pliocene of the Purisima - one I collected with my girlfriend in 2006, and the specimen I collected this summer. The 2006 specimen has one tooth, but is better preserved than this specimen.
This specimen may not represent P. wilsoni; the P. wilsoni holotype is about a million years older, and it is certainly possible that crania from this stratum represent P. sternbergi due to their younger age; description of material from the San Mateo Formation is needed to investigate this further. In fact, a huge body of fossils of Parapontoporia need to be described.
Closeup of the teeth of the new jaw of Parapontoporia wilsoni.

Parapontoporia was originally named for its similarity to the extant La Plata River dolphin, or Franciscana (Pontoporia blainvillei; Barnes, 1984, 1985). However, subsequent studies have placed it within the Lipotidae, as the sister taxon of the now extinct Yangtze River Dolphin (Lipotes vexillifer; Geisler and Sanders, 2003; Muizon, 1988), which was only described in 1918. Parapontoporia has an extremely long rostrum and mandibular symphysis, and *may* have the most teeth of any mammal (which, if it isn't Parapontoporia, I'm sure it's some kind of eurhinodelphid or other longirostrine odontocete from the Chesapeake Group of the east coast).

Wherever Parapontoporia occurs, it dominates the odontocete assemblage - in the Purisima, up to 38% of isolated periotics are referable to Parapontoporia. The most abundantly known odontocete crania from the Purisima belong to this taxon. Interestingly, despite decades of construction in San Diego, there are now more crania of this taxon known from the Purisima than from the San Diego Formation. Many of these Purisima crania are still in concretions, but nonetheless, they exist, and an excellent opportunity for a study of ontogenetic and stratigraphic variation is possible given this sample (a project Nick Pyenson was bugging me to do, but I simply didn't have the time as an undergrad). In fact, I picked up two partial crania this summer (both in nodules, though; one weighed about 55 pounds).

Nick Pyenson (2009) recently published a pretty neat (albeit depressing) paper in marine mammal science about the consequences of the extinction of Lipotes, given its 'colorful' evolutionary history. But this post is long enough as is, and I could do several more posts just on Parapontoporia; I'll save discussion of that paper for later.

BARNES, L. G. 1984. Fossil odontocetes (Mammalia: Cetacea) from the Almejas Formation, Isla Cedros, Mexico. Paleobios 42:1–46.
BARNES, L. G. 1985. Fossil pontoporiid dolphins (Mammalia: Cetacea) from the Pacific coast of North America. Contributions in Science, Natural History Museum of Los Angeles County 363:1–34.
GEISLER, J. H., AND A. E. SANDERS. 2003. Morphological evidence for the phylogeny of Cetacea. Journal of Mammalian Evolution 10:23–129.
MUIZON, C. de. 1988. Les relations phylog`en´etiques des Delphinida (Cetacea, Mammalia). Annales de Paleontologie 74:159–227.
PYENSON, N.D. 2009. Requiem for Lipotes: an evolutionary perspective on marine mammal extinction. Marine Mammal Science 25:714-724.