Wednesday, November 17, 2010

At long last: a new skull of Herpetocetus bramblei

A while ago I posted about some fieldwork I did over the summer regarding a brand new skull of Herpetocetus bramblei. For those of you cetaceophiles, I'm posting pictures of the partially prepared new specimen. As previously mentioned, I suspected the rostrum was offset by quite a bit. Turns out I was right, and it is really offset.
This is after approximately forty hours of preparation, over about two months. I've been really busy working on all sorts of things, including my thesis, and preparation has been going slow. Also, preparation is slightly more difficult due to the much finer sediment - its sandy siltstone - which is hard when dry and easily scraped when damp, although it dries out really, really quickly.

You'll notice a bunch of other offset portions - alas, the skull is a bit more chopped up than I would prefer. That being said, it does look pretty damn cool. All the small fractures and microfaults are left-lateral (sinistral).
The fractures and their relative movement.

I decided to palinspastically restore the rostrum of this skull using photoshop; in addition to left-lateral movement, there's some vertical axis rotation in some of the blocks, so I had to play around with that a bit. Anyway, here's what the complete thing should look like.

And here it is for comparison with my other skull, which is quite a bit larger; I think this new one is from a juvenile. They are reduced to roughly the same size here. In fact, it looks like I could have made the new specimen a bit larger. Herpetocetus has a pretty long schnoz, that's for sure. That's not terribly surprising, given what we know about Piscobalaena.

Friday, November 12, 2010

Shark-bitten dolphin skull

In 2008 I spent the day before Christmas Eve shivered on a cold, wind-blasted California beach prospecting for vertebrate fossils in the Purisima Formation. I was home on winter break, and although it is far more cold where I go to graduate school in Montana (as I write this I'm looking out at the results of our first winter snow), nothing is worse than being wet and miserably cold out on the foggy, windy coast of the golden state (except perhaps being wet and miserable on the Oregon coast, which I've done).

The thrill (or promise) of discovery is more than enough to keep me fueled in the field during the winter. Indeed, when the birds start singing and the snow melts in the spring, most paleontologists start to get field fever - the field season for most vertebrate paleontologists is during the summer months. Anyone who's ever tried to do coastal fieldwork during the summer, on the other hand, is in for a rude awakening. No erosion takes place during the summer, and many of the outcrops are totally buried. The exposures that are above the beach sand level (which is higher during the summer) are typically covered with dust, sand, and grime, which obscures fossils. The storms in the winter months clean this nasty coating off, and transport beach sand into offshore bars, often exposing strata below the beach (I see new fossil localities every winter this way). Winter is my field season.

Historically, I've had really good luck the day before Christmas Eve. It's my last day before Christmas to make it out in the field. The prior year, I found a humongous Carcharocles megalodon tooth (the only specimen known from the Purisima Formation), and discovered a partially articulated fur seal skeleton.

The Christmas Eve dolphin.

At 4pm, the tide was beginning to come back in, and with little over an hour of daylight, it was looking like I was going to come home empty-handed. I went to one last cove before I turned around to head back to the beach. I walked for a few minutes and spotted something in a boulder I had not seen on my way out: a pair of flat bones joined along an articulation that looked suspiciously (even from 20 feet away) like the palate of a dolphin skull. Upon closer examination, yes indeed! It was a dolphin skull in a mollusk shell bed; the width and flatness of the palate suggested it was not Parapontoporia, the most common odontocete in the Purisima Formation. I set about chopping into the boulder; fortunately, most of it was relatively soft. However, an extremely hard calcium-carbonate cemented concretion the size of a basketball had formed over the dorsal surface of the braincase and rostrum, and this slowed digging down. By dusk, the concretion didn't budge. After another half hour, it finally popped out of the boulder, and I lugged the 45 pound block back to my car. Exhausted, I drove home, drank a couple of hard-earned beers with dinner, and passed out.

View of the facial region of the skull.

When it came time to go back to Montana, I decided I would rather take the fossil as a carry-on than risk checking it and picking up a broken fossil that I had paid 25 bucks for thanks to baggage fees. After arriving in Bozeman (with a very sore back and neck from lugging 65 pounds
of luggage through the Denver airport), I almost immediately began preparation (starting, of course, with acetic acid baths for several weeks to soften the concretionary matrix). It took about two months to prepare, and as you can see from the above photos, it is damn beautiful. I initally identified it as something like Haborophocoena - it bears numerous similarities. However, after showing them photos of the specimen at SVP 2009 in Bristol, UK, Olivier Lambert and Giovanni Bianucci both think this represents a basal delphinid rather than a basal phocoenid. I'm inclined to agree with them, although part of my original ID was based on the presence of premaxillary eminences, which this specimen has (a phocoenid character). However, the ascending process of the right premaxilla is in contact with the nasals while the left is not (a delphinid character). Whatever it is, it will require preparation of the ventral aspect, and more careful analysis of the morphology than what I've been able to do thus far. Whatever it is, it appears to represent a new genus and species, and will make a beautiful holotype specimen in the future. During preparation, one curious thing I noticed was a notch in one of the premaxillary eminences (the large pads/bumps in front of the bony nares). I initially dismissed it as a pathology.

The left premaxillary eminence showing linear gouges (red lines) and missing bone.

Upon closer examination (which admittedly did not occur until yesterday, almost two years after collection) it became apparent that the abnormal area had two distinct, paralell linear gouges, and a short, less distinct third one in the middle (this one is still partly filled with matrix). Around these gouges is an area of exposed cancellous bone, where the bone has been removed.

Additional gouges present near the base of the rostrum.

I also found four more gouges present: two long ones, and two short ones; all but one are parallel. In fact, aside from the one gouge seen above trending towards the upper left corner of the photo, all the gouges are parallel. This is a textbook set of shark-inflicted bite marks. There are a lot of papers on this in the literature, documenting shark bites on dolphins, baleen whales, pinnipeds, sea turtles, other shark teeth, mosasaurs, plesiosaurs, dinosaur bones, sea stars, and probably other marine critters as well.

In fact, the first record of these types of trace fossils were actually first documented in the modern environment: on predated and scavenged sea-otter carcasses from Monterey Bay, and reported by Ames and Morejohn (1980). The reported linear gouges, subparallel wavy small gouges, and a specimen including a shark tooth embedded in a sea otter skull. The morphology of the traces along with the tooth identified the culprit as the Great White Shark, Carcharodon carcharias. Two years later, these exact types of traces were identified by Tom Demere and Richard Cerutti (1982) on a baleen whale dentary (of my favorite whale, Herpetocetus!), and identified as "Carcharodon sulcidens" (a taxon now just considered to be fossil Carcharodon carcharias).

It's not clear what type of shark fed on my poor little dolphin, or if it was a case of predation or scavening; from what I've read, the majority of carcasses that exhibit bites have bite marks on the posterior portion of the body, which is just about as far as you can get from the face. This makes total sense, given how a shark would have to bite into a fleeing dolphin during pursuit. Furthermore, it's interesting to note that this bite would have had to go clean through the dolphin's melon (if it had not already decomposed). Anyway, I interpret these traces as drag marks from the apices of the shark's teeth; I suppose later on I can figure out the relative motion of the shark's mouth during the bite (most likely lateral shake feeding). It'll make for a nice short paper some day...

Ames, J. A., and Morejohn, G.V., 1980, Evidence of white shark, Carcharodon carcharius, attacks on sea otters, Enhydra lutris: California Fish and Game, v. 66, p. 196-209.

Deméré, T.A., and Cerutti, R.A., 1982, A Pliocene shark attack on a cetotheriid whale: Journal of Paleontology, v. 56, p. 1480-1482

Sunday, November 7, 2010

Marcus Ross and young earth creationism at the GSA 2010 meeting

Just within the last couple hours an email went out on the VertPaleo listserv, which was copied directly from Joe Meerts' blog, "Science, AntiScience, and Geology", and can be seen here.

Joe Meert reports on an incident at GSA, where Marcus Ross (well known to be a young earth creationist) was presenting non-creationist paleontological research. At the end of Ross' talk, Meert challenged him to explain how it fit into the context of young-earth creationist flood geological nonsense (my paraphrasing).

I'm rather surprised that there were so many people criticizing Meert for giving Ross a hard time or having any sympathy toward Ross at all. I feel a bit sympathetic towards Ross, simply because he does appear to have a genuine case of "scientific schizophrenia", and it must be quite difficult to remember every morning which pair of shoes to put on (functioning academic versus crazy-time fairy tale).

Meert understandably gave Ross a hard time, and for primarily one reason: Ross et al. go back to their creationist audience and say "look, we're real scientists! Our research is valid." And then say the same thing to the Texas board of education (which already has enough medieval loonies on it).

I completely agree with Meert on this: Marcus Ross et al. represent everything we as scientists and educators stand against. I know there's this whole thing called freedom of religion. But, if outside of the sphere of academia you tell people "I'm a real scientist, so you can believe everything I say, including that the flood killed all the dinosaurs" - that's a really, really malicious ethics violation, let alone a conflict of interest. I'm not advocating blacklisting and witch-hunting - but it is safe to say that the way things work currently just isn't good enough.

Granted, I understand GSA must not have any sort of abstract reviewing process - all you need to know is if "Geology of Star Wars" made it into a GSA poster session, young-earth lunacy can as well.

Unfortunately for my field, there seems to be a lot of interest by young-earth creationists in whale taphonomy; that will be covered in upcoming posts. And what happens with regarding citations of this work? Can their work be considered reliable? It certainly cannot be considered objective by any stretch of the imagination. Do we ignore it and not cite it? Do we call B.S.? This is a real problem.

Wednesday, November 3, 2010

A bizarre new pilot-whale relative from the Pliocene of the North Sea

This morning when I woke up I had a nice message on facebook from a friend of mine - a link to a press release on a new fossil dolphin from the North Sea. To be honest (I had just woken up and was still fairly groggy when I first read it) I first saw this beautiful painting below, and not quite realizing it was a painting, the first thing I thought was "whoa, another extant cetacean???"

I then thought, "whoa, that reconstruction looks really weird."

Reconstruction of Platalearostrum hoekmani from Post and Kompanje (2010) by Remie Bakker.

Fortunately, I was easily able to find a link to the pdf for the article (which came out today in the European journal Deinsea) and see why the beast in the painting looks so strange. Post and Kompanje (2010) report on a fragmentary cranium of a bizarre new odontocete. While very incomplete, the preserved portion of the rostrum (="snout") does exhibit some strange features - a very low tooth count (6 sockets/alveoli), a laterally convex toothrow, and an insanely wide lateral 'wing' of the premaxilla, which makes the rostrum wider towards the anterior tip. The maxilla is also not the lateral most portion of the rostrum towards the front - another weird feature (which is shared in the pilot whales, Globicephala, and the extinct Protoglobicephala). The lateral 'wing' of the premaxilla is also pointed 'upwards' (dorsally) a bit, to make the dorsal rostrum surface concave, like a giant spoon. Although totally weird, the rostrum shares a number of features with the pilot whale Globicephala - anteriorly widening premaxillae, rugose bone surface on the premax, a short laterally convex toothrow, and a rostrum that is pretty short and blunt in general. Globicephala in general is already a very strange critter, and Platalearostrum makes it look sober in comparison.

The holotype fossil of Platalearostrum hoekmani (modified from Post and Kompanje, 2010)

Other features (aside from its close affinity with Globicephala) indicate its inclusion within the clade Globicephalinae. The authors curiously chose to use the clade Orcininae - in the usage of Bianucci (2005). Recent molecular analyses have shown the Globicephalinae paraphyletic in the sense that Orcinus is usually not included - and everything else (Globicephala, Feresa, Grampus, Pseudorca, Orcaella) make a monophyletic group. Without Orcinus, it just isn't the Orcininae anymore. Orcininae may be a valid term if fossil taxa like Hemisyntrachelus and Arimidelphis are shown to be sister taxa of Orcinus orca and the extinct Orcinus citoniensis. That being said, Globicephala is not in that group. Which is all the more interesting, suggesting two different clades of delphinids trending toward (relative) gigantism during the Pliocene.

Comparison of Globicephala macrorhynchus and Platalearostrum hoekmani (from Post and Kompanje, 2010)

This article made me pretty happy because I've worked a little on fossil globicephalines from the Pliocene of California. There aren't that many - bona fide delphinid fossils are generally quite rare in the Mio-Pliocene record in California, as opposed to the obscenely delphinid rich (and diverse!) Pliocene fossil record of Italy. Things like Orcinus, Globicephala, Protoglobicephala, Arimidelphis, and Hemisyntrachelus are all already living (not necessarily coexisting) in the world's oceans in the Pliocene, and now we have another weird one on top of this. Certainly it can be said that during the Pliocene, delphinids were experimenting with new "body plans" (loosely using the term) and rapidly diversifying. The Pliocene was a weird time, and boasted a combination of many strange marine mammals which were more derived than extant relatives often with novel anatomical features and adaptations, relatives of modern taxa with wider geographic distributions, and holdovers of archaic taxa which had not yet kicked the proverbial bucket.

Klaas Post, Erwin J.O. Kompanje, 2010. A new dolphin (Cetacea, Delphinidae) from the Plio-Pleistocene of the North Sea. Deinsea 14:1-14

Bianucci, G., 2005. Armidelphis sorbinii a new small killer whale-like dolphin from the Pliocene of the Marecchia river (central eastern Italy) and a phylogenetic analysis of the Orcininae (Cetacea: Odontoceti) - Rivista Italiana di Paleontologia et Stratigrafia 111: 329-344