Bone-eating zombie worms, part 3: Osedax consume more than cetacean bones

Because Osedax were originally identified colonizing cetacean skeletons, they were originally interpreted as being whale-fall specialists. In order to test the hypothesis that Osedax are cetacean carcass specialists, Jones et al. (2008) experimentally deployed cow bones on the seafloor in Monterey Bay. They attached cow bones to a PVC “tree” on the seafloor, so that the bones would not be in contact with the sediment (with the chance of being covered in sediment. Within a year, the bones were colonized by Osedax. As cow skeletons are probably not typically delivered to the deep sea floor – although given the presence of rare land mammals and dinosaurs in marine fossil assemblages, it does happen, albeit rarely – it suggests that Osedax is not really a cetacean specialist, and can colonize the bones of other mammals. Jones et al. (2008) suggested that Osedax not only colonize the skeletons of baleen whales, but also bones of dolphins, porpoises, sea lions, and seals that reached the seafloor. They further suggested that future experiments should include other-non cetacean bones. One could make the observation that large, domesticated artiodactyls are not only closely related to cetaceans, but also have fatty bones; so perhaps it’s not surprising that cow bones make appropriate habitat for bone eating worms.

 

Modern cow bones implanted on a PVC "tree" on the seafloor, with closeup of Osedax worms emerging from the bone. From Jones et al. (2008).

This paper seemed to stir up some controversy, and generated a sharp response by Glover et al. (2008) who commented on several aspects of the study which may (or may not…) invalidate observations of cow bone colonization. They argue that Osedax probably qualifies as a whale-fall specialist, because whale skeletons comprise the majority of its “diet”. They indicated that no whale fall assemblages had been identified on naturally occurring terrestrial mammal carcasses in the deep sea. They also argued that the placement of cow bones on a metal tree above the seafloor does not represent a naturally occurring condition; they indicate that the small bones of land mammals would probably be buried too quickly to be colonized by Osedax. I’m not necessarily certain this is really evidence that Osedax wasn’t a generalist, but the inferred rarity of terrestrial vertebrate remains on the seafloor is probably reasonable to cite as evidence of Osedax being a whale fall specialist. Curiously, Glover et al. (2008) make the comment that actualistic taphonomy of large land mammals shows that they are unlikely to be transported far by rivers. This is perhaps amusing when one recalls how many fossils we have of land mammals and dinosaurs in marine rocks – examples from my neck of the woods include a skull of the dome-headed chalicothere Tylocephalonyx from the marine Astoria Formation of central Oregon, and the type skeleton of Aletopelta from the late Cretaceous of San Diego County (a.k.a. the “ankylosaur ass”, as affectionately referred to by some SDSU students). Furthermore – in one of Jack Horner’s first papers, he reviewed the dinosaur record from the late Cretaceous Bearpaw Shale of Montana, and found that numerically more nodosaurid skeletons were known at the time from marine rocks than from terrestrial rocks.

Vrijenhoek et al. (2008) responded to the complaints of Glover et al. (2008) and noted the age-old adage that ‘absence of evidence is not evidence of absence’, and is certainly an excellent point in this case: the lack of discoveries of terrestrial mammal ‘falls’ is probably not a good indication of their existence of not: Glover et al. argued that Osedax may not effectively colonize land mammal bones due to their small size, and it is important to note that the same argument can be flipped on its head – small bones are less likely to be discovered on the seafloor by ROV’s or submersibles. Contrary to the assertion of Glover et al. (2008) that land mammals do not frequently travel long distances in rivers (and thus float out into the sea), Vrijenhoek et al. (2008) report on a pelvis and several hind leg bones of a large mammalian herbivore off the coast of New Guinea at a depth of 1500 meters, discovered by submersible. These bones were also colonized by Osedax, interestingly. Not only does this indicate that Osedax will colonize “naturally” occurring land mammal bones, but also that such occurrences are ‘findable’. Vrijenhoek et al. (2008) report that rice was found on the seafloor around the bones, and they interpreted it as discarded waste from a passing ship; furthermore, the pelvis shows a distinct butcher’s sawmark, indicating it did not arrive naturally.

 

Partial hindlimbs of a terrestrial mammal found on the seafloor, complete with Osedax... and a pile of rice? This appears to represent waste chucked overboard a ship. From Vrijenhoek et al. (2008).

 

A beautifully sculpted model of the giant Japanese plotopterid, Copeteryx. Sculpted by Hirokazu Tokugawa (from a-fragi.blogspot.com). Oligocene bones of a close relative from Washington state- Tonsala - have been found with trace fossils identifiable as Osedax.

In late 2010, Steffen Kiel and colleagues published another article on fossil Osedax borings – this time on early Oligocene bird bones from the Olympic Peninsula. These were bones of the extinct bird Tonsala hildegardae – a flightless, penguin-like plotopterid bird. Plotopterids such as Tonsala, Copteryx, Hokkaidornis, and Plotopterum are gigantic birds that went extinct during the Miocene; they are known from Japan, California, Oregon, Washington, and British Columbia. These giant birds were up to 2 meters in height, and represent the Northern Pacific analogs of giant Paleogene penguins (e.g. Kairuku, Icadyptes, Platydyptes). Bones of Tonsala were found to have numerous small Osedax pinholes, in addition to typical Osedax borings when CT-data were examined. To recap from part 2, these boreholes are where the Osedax stalks and gills extend out from the bone; below, the borings are confluent with bioeroded galleries roofed over by thin walls of outer (cortical) bone left. Not only does this further indicate that Osedax has naturally colonized non-cetaceans through the course of geologic time, but also that Osedax would have had a suitable source of bones prior to the Eocene evolution of cetaceans. This further suggests that a Cretaceous rather than Eocene divergence date of modern Osedax species (these are the two hypothesized divergence dates in the literature, depending upon which calibration is used).

 

Plotopterid bone with characteristic Osedax "pinholes". Early Oligocene of Olympic Peninsula, Washington State. From Kiel et al. (2011).

 

 Fossil record of large marine birds during the latest Cretaceous and Paleogene; these birds may have bridged the gap for Osedax between the extinction of large marine reptiles and the emergence of large, oceangoing cetaceans in the middle Eocene. From Kiel et al. (2011).

The next year, Rouse et al. (2011) published a short paper on another experiment in order to further test the whale-specialist hypothesis. Rouse et al. experimentally deployed large fish bones in small wire cages, and observed Osedax colonization after only 5 months. This is far more surprising than cow bones, as fish bones have avascular histology (i.e. dense bone without pore space), which is perhaps as far from the lipid-rich, osteoporotic bones of cetaceans that you can get among vertebrates. This not only lends support to the idea that Osedax may naturally colonize non-cetaceans, but also that non-cetacean bones (such as those from birds and bony fish) would have sustained Osedax during the Paleocene and early Eocene, after marine reptiles went extinct but before large oceangoing cetaceans evolved.

 

Fish bones experimentally deployed on the seafloor, and hosting Osedax worms, indicating they have a much taxonomically wider palette of bony substrates for colonization and consumption. From Rouse et al. (2011).

All in all, it appears as though modern Osedax probably does occur most commonly on whale skeletons rather than other vertebrates, but that it has colonized the remains of other vertebrate groups through time. Unfortunately, our fossil record of Osedax boreholes is restricted to a handful of bones from the Oligocene and Pliocene; the real test of Osedax evolution will be in the Eocene and Late Cretaceous. On one hand, I somewhat doubt that we will find Cretaceous Osedax borings, if they have not been identified as of yet. On the other hand – the fact that Osedax borings are so small, and have only been in the collective conscience of marine vertebrate paleontologists for only a year or two, they may legitimately be unidentified in currently established fossil collections of late Cretaceous marine reptiles. If we don’t find late Cretaceous Osedax, it might be reasonable to hypothesize that they arose with Eocene cetaceans, as proposed by some biologists.

Don't forget to see the rest of the series:

Bone-eating zombie worms, part 4: more on bird bones, and Osedax colonizes whale teeth

Bone-eating zombie worms, part 2: the discovery of fossil Osedax traces

Bone-eating zombie worms, part 1: whale falls and taphonomy


References:

Glover, A. G., Kemp, K. M., Smith, C. R.; Dahlgren, T. G. 2008 On the role of bone-eating worms in the degradation of marine vertebrate remains. Proc. R. Soc. B.  275:1959–1961.

Jones, W. J., Johnson, S. B., Rouse, G. W. & Vrijenhoek, R. C. 2008 Marine worms (genus Osedax) colonize cow bones. Proc. R. Soc. B 275, 387–391.

Kiel, S., Kahl, W. A. & Goedert, J. L. 2010 Osedax borings in fossil marine bird bones. Naturwissenschaften 55:51–55.

Rouse, G.W., Goffredi, S.K., Johnson, S.B., and R.C. Vrijenhoek. 2011. Not whale-fall specialists, Osedax worms also consume fishbones. Biology Letters 7:736-739.

Vrijenhoek, R.C., P. Collins, and C. Van Dover. 2011. Bone-eating marine worms: habitat specialists or generalists? Proceedings of the Royal Society B. 275:1963-1964.

Bone-eating zombie worms, part 2: the discovery of fossil Osedax traces

 

A schematic showing a 3d model of an Osedax bone boring. (Source: University of Leeds)

After taking a taphonomy course during my undergraduate program – roughly a year after Osedax was discovered – I had come across several references to bone eating worms. But because only a few papers had been published on fossil whale falls, and whale falls appear to be relatively rare in the fossil record, I didn’t really seriously expect traces of Osedax worms to be found in fossils. Surprisingly, I only had to wait five years. In 2010, a number of papers were published regarding possible Osedax traces – and what modern Osedax borings look like.

To start with – the first fossil record of whale falls was reported not very long after the first modern whale falls were reported. Squires et al. (1991) reported on Oligocene cetaceans  preserved with chemautotrophic mollusks, which were closely related to mollusks already known from cold seeps. Subsequently, a number of other fossil whale fall assemblages were reported (Goedert et al., 1995; Amano and Little, 2005; Pyenson and Haasl, 2007).

In February 2010, some borings were reported from Miocene baleen whale bones from Spain; they were cylindrical, up to 5cm deep and 1-3mm across, with numerous teardrop-shaped lobes internally. These were interpreted by the authors to represent Osedax worm borings (Muniz et al., 2010). Furthermore, the authors were able to name a new ichnospecies – trace fossils are given Linnean binomial names in ichnotaxonomy, a parataxonomic system. They named the trace fossil Trypanites ionasi; other ichnospecies of Trypanites are borings in hard substrates.

 

Traces of Trypanites ionasi, from the Miocene of Spain. From Muniz et al. 2010.

 

Reconstruction of Osedax happily producing Trypanites ionasi traces in bone. From Muniz et al. 2010.

A few months later, in April – Steffen Kiel, Jim Goedert, and colleagues reported on possible Osedax traces in Oligocene cetacean bones from the Olympic Peninsula. More importantly, they also reported on what exactly modern Osedax borings actually look like – data which had not yet been published in the whale fall literature yet. The borings that Kiel et al. (2010) reported on from modern and fossil whale bones had tiny boreholes in the cortical bone surface, and the cortical bone was bioeroded into large coalesced galleries underneath the exterior bone surface. Where the borings coalesced, only the outermost layer of bone was left as a thin veneer. In life, the stalks exit the bone through the tiny boreholes, and the “roots” occupy the bioeroded galleries. The modern and fossil traces were analyzed by CT scans, used to construct 3d models of the borings.

 

Bona fide fossil Osedax traces in Oligocene whale bones from Washington State, from Kiel et al. (2010); compare these with those from Muniz et al. (2010), above.

Oddly enough, these borings don’t really resemble those reported by Muniz et al. (2010) – at all. It is certainly feasible that those reported by Muniz et al. are some other species of Osedax, and we only have a few examples of published modern Osedax traces. However, the fact that Oligocene and modern traces are nearly identical suggests that there is some degree of conservatism in boring shape. So, who really knows what made the traces in the Spanish whale bones. It’s understandable, as the authors of that study didn’t report on what modern Osedax traces look like – a necessary stepping stone for interpreting fossil remains. As an aside, one of the authors of that study – Raul Esperante – is a well known young-earth creationist from Loma Linda Univerisity in southern California who has published a series of articles on whale taphonomy.

 

Finally, examples of Osedax traces from a modern bone: from Higgs et al. (2010).

 

More examples of modern Osedax traces, from Higgs et al. (2011).

More work on modern Osedax traces was published by Higgs et al. (2010). They also used CT scans to construct 3d models of the borings, and reported borings that were roughly similar to that reported by Kiel et al. (2010). Higgs et al. (2010) further found that the borings were mostly restricted to dense cortical bone, generally avoiding lipid-rich cancellous zones. Apparently some isotopic evidence suggests that Osedax synthesizes collagen rather than lipids, although other studies have documented Osedax in Japanese waters that subsist on blubber and spermaceti (Higgs et al. 2010 – references therein).

 

The (awesome) t-shirt Nick Higgs wore to SVP in 2009. The few marine vertebrate taphonomists at SVP - myself included - found this guy pretty damn quick. 

I met Nick Higgs at the 2009 SVP meeting in Bristol, UK – I was chatting with my friend and colleague Laura Vietti (Macalester College/University of Michigan), who is also focused on marine vertebrate taphonomy – and this British guy about our age came up to us, literally wearing a T-shirt he had made which said “bone eating worms” with a picture of Osedax infested whale bone on the back, and text saying “Lets talk: whale taphonomy!” Needless to say, he found Laura and myself really darn quick. Nick has subsequently invited us both to co-write a review paper on marine vertebrate taphonomy, which is an exciting opportunity to say the least.

 

 A beaked whale radius from the Pliocene of Tuscany, Italy, with numerous Osedax traces and pockmarks. From Higgs et al. (2011).

 Osspecus tuscia traces from the Pliocene beaked whale bone. From Higgs et al. (2011).

 

More recently, Nick Higgs and colleagues (2011) published another paper on early Pliocene Osedax borings in a beaked whale radius from Italy. This fossil exhibited a number of different types of borings, which were interpreted as different stages of borings. Some borings in CT-scans were well defined, with small apertures as in Kiel et al. (2010) and Higgs et al. (2010). Other pits had a small bit of bone caved in around the aperture (collapsed stage), while other pits retained no overhanging bone (open-pit stage); the last type has been eroded to the point where it looks like a crater (pockmark stage). Some pits had coalesced, forming combined pits. Higgs et al. (2011) also named a new ichnotaxon for these Osedax borings: Osspecus tuscia.

 

Two modern cetacean bones bored by Osedax. What's the significance of this figure from Higgs et al. (2011)? Stick around for part 4.

Although borings of Osedax have now been documented from the fossil record, what exactly does it mean for taphonomy? And what does it mean about the evolution and earliest record of Osedax? Tune in for parts 3 and 4.

Don't forget to check out the rest of the series:
  
Bone-eating zombie worms, part 4: more on bird bones, and Osedax colonizes whale teeth


Bone-eating zombie worms, part 3: Osedax consume more than cetacean bones

Bone-eating zombie worms, part 1: whale falls and taphonomy

References:

Amano, K., C.T.S. Little. 2005. Miocene whale-fall community from Hokkaido, northern Japan. Palaeogeography, Palaeoclimatology, Palaeoecology 215:345-356.

Goedert, J.L., Squires, R.L., Barnes, L.G., 1995. Paleoecology of whale-fall habitats from deep-water Oligocene rocks, Olympic Peninsula, Washington state. Palaeogeography, Palaeoclimatology, Palaeoecology 118: 151– 158.

Higgs, N. D., A. G. Glover, T. G. Dahlgren, and C. T. S. Little. 2010. Using computed tomography to document borings by Osedax mucofloris in whale bone. Cahiers de Biologie Marine 51:401-405.

Higgs, N.D., C.T.S. Little, A.G. Glover, T.G. Dahlgren, C. R. Smith, and S. Dominici. 2011. Evidence of Osedax worm borings in Pliocene (~3 Ma) whale bone from the Mediterranean. Historical Biology 24:269-277.

Kiel, S., J. L. Goedert, W. Kahl, and G. W. Rouse. 2010. Fossil traces of the bone-eating worm Osedax in early Oligocene whale bones. Proceedings of the National Academy of
Sciences 107:8656-8659.

Muniz, F., J. M. d. Gibert, and R. Esperante. 2010. First trace-fossil evidence of bone eating worms in whale carcasses. Palaios 25:269-273.

Pyenson, N.D., D.M. Haasl 2007. Miocene whale-fall from California demonstrates that cetacean size did not determine the evolution of modern whale-fall communities. Biology Letters 3:709-711.

Squires, R.L., Goedert, J.L., and Barnes, L.G. 1991. Whale carcasses. Nature 349:574.

Bone-eating zombie worms, part 1: whale falls and taphonomy

 

 

How do we interpret the preservation of fossil marine vertebrates, like this Dorudon atrox skeleton from the Eocene of Egypt? (From Peters et al., 2011)

Unless you've lived in a cave for the last two decades or hate science and the oceans (or all of the above), you've probably heard about whale falls. Whale falls are one of the more fascinating aspects of modern marine biologic research. They were only discovered relatively recently (late 1990's) and research conducted by submersible and ROV has uncovered an amazing fauna that quickly develops around sunken whale carcasses. Biomass is present in relatively small amounts on the seafloor, and much of the food for critters on the abyssal plain rains down from the more densely populated upper part of the water column. When whales die – and sink – most of the time their carcasses will sink down to the seafloor. But whales aren't very common, and although whales die every day – the introduction of a whale carcass to the seafloor, from the vantage point of a seafloor organism – is not an everyday affair. Seafloor ecology is mediated by the introduction of food, and whale carcasses represent the most locally concentrated pulse of food in the deep sea.

 

Whale vertebrae and a hagfish at a whale fall. From www.mbari.org

As a paleontologist, much of the hullabaloo about whale falls is only of cursory interest; many of the ecological details – species diversity at whale falls, similarity to vent and cold seep fauna, interactions between invertebrates – are not really of much practical interest to a vertebrate paleontologist like myself. Certainly these other issues are totally fascinating – but I'm really only going to talk on here about the stuff that interests me as a paleontologist, as you can easily get the perspective of a biologist or ecologist elsewhere on the web.

 

 Photograph of a whale fall hosting a large number of bone-eating worms (Osedax).

So why am I so interested in whale falls? Whale fall research has generated some seriously intriguing information regarding the taphonomy of marine mammals (cetaceans in particular; see Allison et al., 1991). Admittedly, not all vertebrate paleontologists (marine mammal researchers included) are not terribly interested in taphonomy. Taphonomy is the science of fossil preservation, and is often summed up as attempting to discover everything that happened to a fossil from "death until burial" (and sometimes, after burial: diagenesis). This is a serious problem, as any paleontologists who hope to do field-based research need a strong (or even mediocre) background in taphonomy. I find taphonomy to be, on one hand – relatively intuitive, and on the other hand – more intellectually stimulating than bread and butter phylogenetics (this is not a slam against cladistics; I just find taphonomic problems more interesting and challenging). 

A painting of a whale fall assemblage. From www.mbari.org

Taphonomy is also very important if a paleontologist is interested in anything relating to paleoecology: with respect to a fossil, paleoecologic information can generally be preserved intrinsically (functional anatomy, oxygen/carbon isotopes, etc.) or extrinsically (gut residues, coprolites, feeding traces, juvenile/adult or other social associations, etc.). The former category is more or less decoupled from taphonomy, as it generally pertains to information not affected by taphonomic loss. However, once a paleontologist wants to start talking about the nature of a fossil assemblage, and whether it represents a mass death assemblage, a nesting ground, or evidence of feeding behavior, these issues extend outside the bones themselves, so to speak, and into tangential issues affected by processes of preservation. To say anything regarding paleoecology and using extrinsic information, a paleontologist had better do his or her damned homework; there are plenty of examples in the published literature of non-taphonomists saying some pretty silly things.

Because I study fossil marine mammals, whale falls provide a wealth of data regarding what happens to a whale after it dies on the seafloor. So, what does happen? To sum it up, in a way – a multitude of organisms rush in to eat it. Whale fall faunas appear to show a series of successive stages (Smith and Baco 2003):

1) Mobile scavenger stage: large scavengers such as fish, sharks, hagfish, chimaeras, and invertebrates feed (rapidly) on whale soft tissue.

2) Enrichment opportunist stage: organically enriched sediment and exposed bones are colonized by opportunistic polychaetes and crustaceans.

3) Sulphophilic stage: a trophically complex assemblage of nearly 200 species of invertebrates and microorganisms inhabit the skeleton while lipids in the bones undergo anaerobic breakdown and emit sulphides.

A fourth stage – the reef stage – has been hypothesized for late-stage whale falls (Smith, 2006) that are chemically inert, so to speak – and colonized by sessile invertebrates taking advantage of higher elevation (and thus currents) above the seafloor. However, no evidence for this stage currently exists and it is purely hypothetical.

 

A group of Osedax stalks and gills growing in a whale bone. From www.mbari.org

In particular, modern whale falls have benefited taphonomists by providing valuable information regarding rates of scavenging and the timing of skeletonization (exposure of bones in a carcass) as well as rates of bone degradation, burial, and the types of organisms that may leave a physical trace record of their colonization. In 2004, a new type of whale fall specialist was discovered infesting the bones of a baleen whale skeleton off the coast of California: a bone-eating “zombie” polychaete worm, named Osedax (Rouse et al., 2004). It was discovered in massive amounts on bones, with reddish gills mounted on stalks emanating from small holes in the bone. Roots of the worm extend into the bone, and host symbiotic bacteria to synthesize nutrients from the bone. It is currently debated exactly what Osedax feeds upon: lipids in the bone, or collagen. Since 2004, a number of species of Osedax have been discovered, and are now known worldwide from deep marine whale falls. If this parade of weirdness wasn’t enough, the males are dwarfs, never leave the larval stage, and live on/in the females.

 

An individual Osedax worm separated from its bony home. From www.mbari.org

In the next few posts, I’ll cover several issues, including the discovery of Osedax traces in fossil bone (part 2), Osedax colonization/consumption of other types of vertebrates (part 3), and implications for taphonomy and possible “megabias” in the fossil record (part 4).

I highly recommend watching this video: it's not educational, per se, but if you're familiar with whale falls, it is delightfully animated. Whale Fall (afterlife of a whale).

Don't forget to see the rest of the series:

Bone-eating zombie worms, part 4: more on bird bones, and Osedax colonizes whale teeth

Bone-eating zombie worms, part 3: Osedax consume more than cetacean bones

Bone-eating zombie worms, part 2: the discovery of fossil Osedax traces

References:

Allison, P. A., C. R. Smith, H. Kukert, J. W. Deming, and B. A. Bennett. 1991. Deepwater
taphonomy of vertebrate carcasses: a whale skeleton in the bathyal Santa Catalina
Basin. Paleobiology 17(1):78-89.

Peters, S. E., M. S. M. Antar, I. S. Zalmout, and P. D. Gingerich. 2009. Sequence
stratigraphic control on preservation of late Eocene whales and other vertebrates at Wadi
Al-Hitan, Egypt. Palaios 24:290-302.

Rouse, G. W., S. K. Goffredi, and R. C. Vrijenhoek. 2004. Osedax: Bone-eating marine
worms with dwarf males. Science 305:668-671.

Smith, C. R., and S. R. Baco. 2003. Ecology of whale falls at the deep-sea floor.
Oceanography and Marine Biology: an Annual Review 41:311-354.

Smith, C. R. 2006. Bigger is better: the role of whales as detritus in marine ecosystems.
Pp. 286-302. In J. A. Estes, D. P. DeMaster, D. P. Doak, T. M. Williams, and R. L.
Brownell, eds. Whales, Whaling and Ocean Ecosystems. University of California Press,
Berkeley, CA.

Spring in Otago

I'll admit I had originally planned on spending a couple hours tonight typing about bone eating worms and their impact on the fossil record, but I came down with a fairly severe headache this afternoon that is still fairly intense. Instead, I'll leave you with a couple of pretty pictures from outside my office.

 While all of you folks in the northern hemisphere have been enjoying your summer, my wife and I have completed our 10th straight month of winter - just as spring was starting in the US we flew down here, just as winter was beginning again in the south. This winter was nothing compared to the nastiness we left behind in Montana, but it is a bit of a bummer not really being able to go outside in a t-shirt and shorts for nearly a year (not that it stops kiwis, who will walk to campus in shorts and barefoot as long as its not raining and at least a few degrees above freezing).

This beautiful magnolia tree started blooming last week; it has got to be one of the prettiest plants I've ever seen before. I hope the flowers last more than a few days or so.

Field work in South Canterbury

Late last week I went with Ewan, fellow student C. H. Tsai, and fossil preparator Sophie White on a day trip to North Canterbury, to one of Ewan's most productive fossil localities in the Otekaike Limestone. We got up early and packed the department vehicle and trailer with all manner of equipment, including the masonry saw and the equipment Ewan Fordyce is famous for within paleontological circles - a chainsaw. The rock is so soft that it can be sawn through with a chainsaw fitted with a diamond-dust coated chain, which Ewan estimates has cut the amount of time needed for digging by 70% or so. Unfortuantely I don't have any photos of the fieldwork, as I left my camera at home. It turned out that we were so damn busy I wouldn't have had time to take many photos anyway.

There has been quite a bit of rain here on the South Island over the past few weeks, and Ewan had planned on making a trip up there anyway - just not so soon, as he wanted to wait for some even drier weather. Upon arriving at the quarry, we found a few bits of bone here and there, but at first, nothing too promising.

One fossil included both mandibles of a medium-sized baleen whale (est. 2 meter skull length?), and will require a large jacket, at least 1.5 m long. I found a probable odontocete mandible (probably not very complete), and a couple of bird bones. One specimen that I poked around at initially looked like an odontocete rib, but very quickly turned into a disarticulated penguin skeleton. This is probably not something like the recently described penguin Kairuku - which is well known from the older, underlying formation called the Kokoamu Greensand - but, according to Ewan, may turn out to be Platydyptes novaezealandiae, which is well known from the Otekaike Limestone.

The most exciting find of the day started out not very promising at all: a cluster of dolphin ribs and vertebrae. Sophie started cleaning it up and uncovered a nearly complete radius. I developed a pretty solid headache and as a result was working fairly slowly, but helped Sophie as best I could with the dolphin. After a while she uncovered a weird, large, conical element, and asked me what I thought it was; after a little more exposure, it was very clearly the rostrum of a medium-sized odontocete (something about the size of modern Tursiops). After a bit more cleaning, Sophie found the vomer and internal choanae, the squamosal, and a paroccipital process (exoccipital bone): they were in place, and indicated that the entire skull is present. This was very exciting; there is a large assemblage of odontocetes from the Otekaike, including a large squalodont, small tusked dalpiazinids, a squalodelphinid (labmate Yoshi Tanaka is working on these), Notocetus marplesi (considered by Fordyce (1994) to be a Waipatiid), the strange and beautifully preserved dolphin Waipatia, and a smattering of other very strange and incompletely known (but tantalizing...) taxa I won't talk about any further. The weirdest part about this dolphin was the rostrum: it was very short, and apparently toothless. The skeleton includes the skull, a mandible, radius, many vertebrae and ribs, and a scapula.

We finished the day off by excavating everything but the block with the dolphin and the baleen whale; we would have to return later to excavate those. We left with a half dozen small blocks and two plaster jackets (the penguin skeleton and another partial dolphin). At the moment, Ewan is getting ready to return to the field (tomorrow), with Tsai, Yoshi, and Sophie; over the weekend, I started getting some strange rashes caused by a chicken pox-like virus, and won't really be able to make it out into the field with them, unfortunately.

New Zealand field work: Paleocene of Wangaloa

Last week, Ewan invited two other students and I to do some fieldwork on the coast south of Dunedin. We would go prospecting in lower Paleocene (er... Palaeocene) strata, approximately 62 Mya (pretty old stuff!). This is a particularly interesting period of time in general due to faunas recovering from the K/Pg extinction and reduction in competition and selective pressures for some clades, but the Paleocene of New Zealand has already yielded a number of interesting shark finds, and most importantly - the world's oldest and most primitive penguin fossils (Waimanu).

Yoshi Tanaka along the cliffs. Our target is the point in the distance and the stacks of concretions on the shoreline.

My adviser Ewan Fordyce examining the base of the cliffs.

Yoshi and I using the pionjar rock drill to extract a small vertebrate bone (or tooth).

Ewan using the rock drill. The drill weighs about 70 lbs, has an 18" bit, and is a percussive drill: it is effectively a combination drill and jackhammer. In other words, it's a jackhammer with a rotating chisel bit.

The skeletal element in question is in a shell-rich unit in extremely hard, calcium carbonate-cemented sandstone, and located about 4-5" to the right of the bit. We're drilling a couple holes here in a layer just below it.

Due to the low rotation speed of the bit, someone with gloves (Ewan in this case) can hold the bit in place in order to start a bore hole.

The rock drill is a bit of a beast to work with and bucks around a lot while at the same time being awkwardly proportioned and weighted and spitting out oil and foul smelling exhaust; it is relatively straightforward to use vertically, but using it at an angle is a constant struggle.

Fellow student Cheng-Hsiu Tsai starts a second bore hole.

Step two: after the bore holes are drilled, pairs of wedges with a half-circle cross section are placed in, and a wedge between them.

Another view of the wedges. At this stage, the wedges can be driven in by hammer (the long way), or a non-rotating "hammer bit" can be placed into the business end of the rock drill. This bit has a cup on the end, and if properly coaxed, will hammer the wedge into the rock. With two wedges, the rock drill has to be alternated from one to the other to ensure even splitting.

Yoshi (left), myself (middle), and Tsai (right) examining a tiny bit of bone in a very, very large boulder.

This was a pain in the ass: at shoulder height, three people are required, and a hook can be looped over a support - in this case an estwing "super pick"; not only does this allow for support, but the two can also use the cross beam support to push the drill into the rock. Minutes later, Yoshi unfortunately found another bone - this time, at eye level.

Yoshi (right), Tsai (middle) and myself (left) after an arduous walk back with ~120 pounds of rock drill & bits and wedges, and ~60 pounds of concretion fragments (with tiny bones). Tsai had some awesome oil splatter on his face (from the rock drill) which is only partially cleaned off here.

Parabalaenoptera baulinensis: the fossil baleen whale from Bolinas, Marin County, California

Until relatively recently, fossil balaenopterids have been avoided by modern paleocetologists like the plague. Modern balaenopterids include the humpback whale (Megaptera novaeangliae) and species of Balaenoptera, including the Minke, Blue, Fin, and Sei whales. Although balaenopterids have very distinctive and easy to identify crania, they are really only common in latest Miocene and Pliocene marine rocks, and early work by Kellogg and others yielded fossil baleen whales with much more primitive skulls, formerly called "cetotheres" sensu lato, also jokingly referred to by some paleocetologists as "Kelloggitheres".

Fossil balaenopterids have been plagued by a particularly nasty taxonomic situation since the late nineteenth century, when P.J. Van Beneden began describing fossil mysticetes collected during the construction of a series of forts around Antwerp. Unfortunately, many of these fossils which names like Plesiocetus and Herpetocetus are based upon were isolated finds, which were subsequently arranged into type 'series' with other skeletal parts based on a preconceived notion of what each taxon should have looked like. The end result was a series of chimaeras, some of which represented by potentially informative but often fragmentary material, lacking type specimens, the associated names of which have been dragged through the systematic mud by subsequent authors, and not allowed to simply die gracefully.

 

The skull and mandibles of the holotype specimen of Parabalaenoptera baulinensis from the late Miocene Santa Cruz Mudstone of Marin County, California.

Many of these fossil balaenopterids are difficult or impossible to diagnose: which specimen of the series would you designate as a lectotype? Is that specimen diagnostic? What do you do with the other specimens? Is an isolated mandible diagnostic or not? What about a piece of a braincase with unassociated bullae? According to Bosselaers and Post (2010), many of Van Beneden's taxa are based on "syntype" collections that are not possible to unambiguously diagnose: diagnostic syntype elements are either too incomplete, or include multiple diagnostic elements but from multiple individuals (and occasionally taxa; i.e. a balaenid bulla was grouped with the lectotype mandible of Herpetocetus scaldiensis by Van Beneden). Accordingly, Bosselaers and Post (2010) declared all of Van Beneden's Pliocene balaenopterid taxa to be nomina dubia: for the time being, I think this is probably the "safe", appropriate, and right thing to do.

The discovery and description of Parabalaenoptera baulinensis was one of the first important advances in balaenopterid paleontology: it was one of the first balaenopterids described from a nearly complete skull with associated mandibles and postcrania. Some other previously published fossil balaenopterids were described on somewhat complete remains: Megaptera miocaena (late Miocene of California), Megaptera hubachi (late Miocene of Chile), Protororqualus cortesii (Pliocene of Italy), "Balaenoptera" cortesi var. portisi (Pliocene of Italy), and Cetotheriophanes capellinii (...also Pliocene of Italy). Unfortunately, the holotype skeleton of Protororqualus was destroyed during bombing in World War II, and M. miocaena only includes earbones and a braincase; furthermore, the other Italian balaenopterids have been plagued with nomenclatural issues for over a century (see Demere et al. 2005).

The exhibit at the Drakes Beach visitor's center showing the holotype skeleton of 

Parabalaenoptera baulinensis.

In 1973, a large mysticete skeleton was discovered by Carl Zeigler of the College of Marin, weathering out of cliffs near Bolinas in Marin County, California. Bolinas is a quaint artist community on the Marin County coast and has changed little since the 1960's and 70's; it is predominantly settled by ex-hippies, who generally don't like visitors from out of county, and have continually removed the exit sign for "Bolinas: 2 miles" off of highway 1, to the point where the California Dept. of Transportation (CalTrans) has given up putting up new signs. Tales abound of visitors with out of county or out of state license plates having car tires popped or vandalized, and nails and other tire-popping objects being intentionally laid out onto dirt roads in town. My car had a San Rafael Honda license plate holder, so I never had this problem.

 

The assembled holotype skull of Parabalaenoptera at California Academy of Sciences, photographed by fellow Otago Ph.D. student Felix Marx.

Exposed along the southern tip of Point Reyes is a unit formerly identified as the early late Miocene Monterey Formation; this was subsequently reevaluated after Domning (1978) suggested that sea cow fossils from the Bolinas locality were too derived to be from such an old unit. Afterwards, microfossils suggested a much younger age, closer to the Mio-Pliocene boundary (6-6.8 Million years old), and the formation was reidentified as the Santa Cruz Mudstone, which has only been mapped in Santa Cruz County.

 

Anterior view of Parabalaenoptera.

The fossil occurred in indurated, blocky mudstone, and was collected over a ten year period as the blocks incrementally eroded from the cliff. The lead authors - Gordon ("Gordie") Chan and Carl Zeigler of the College of Marin in Kentfield, and their field assistants - would have to travel over the hill and out to Bolinas (nearly an hour's drive through some of the windiest vomit-inducing roads in Northern California) on a monthly basis during the summer, and much more often during the winter during periods of intense erosion, and sometimes daily, anticipating falling blocks. After collection, the blocks were prepared, and some were glued together - but left as a series of blocks that could be lined up and assembled. The holotype was prepared at College of Marin, and eventually molded, casted, and donated to the California Academy of Sciences. Mounted casts of Parabalaenoptera baulinensis are currently on display at College of Marin in Kentfield and at the Drake's Beach visitor center at Point Reyes National Seashore. Sadly, before the paper could be published on the fossil - Carl Zeigler and Gordon Chan passed away. Chan passed away in 1996 of Lou Gehrig's disease; I could not find information on Zeigler, though I seem to recall hearing that he was killed by a drunk driver. Dr. Lawrence Barnes of the Los Angeles County Museum of Natural History finished the manuscript and brought it to publication in the California Academy of Sciences in 1997.

 

The braincase and vertex of Parabalaenoptera.

Parabalaenoptera baulinensis is a medium-sized balaenopterid with a 2.2 meter skull, slightly larger than minke whales (Balaenoptera acutorostrata; a 10 meter long whale with a 2m skull), but has a number of features that are too divergent to warrant inclusion within humpbacks (Megaptera) or Balaenoptera. These include the very elongate and somewhat swollen zygomatic processes, narrow intertemporal region (the skull is less 'telescoped than in modern balaenopterids), and extremely long and narrow nasal bones. The mandibles are strongly outwardly bowed like in Megaptera, and have an elongate coronoid process - somewhat like blue and fin whales (Balaenoptera musculus and physalus). Many of these features suggest that Parabalaenoptera baulinensis was capable of lunge feeding just like modern rorquals. It is additionally convergent with Balaenoptera musculus in having a supraorbital process of the frontal that is somewhat triangular and narrows laterally, whereas in Balaenoptera and Megaptera, the posterior and anterior margins are either parallel, or the posterior margin is perpendicular to the midline. Unfortunately, the holotype specimen is not preserved very well, and it appears that a significant amount of bone was accidentally removed or ground away during preparation, and details of the basicranium are almost totally indiscernible. Parabalaenoptera has been found in many phylogenetic analyses to be a stem-balaenopterid - in other words, a primitive member of the clade (family Balaenopteridae) that does not belong to the clade formed by humpback whales and modern species of Balaenoptera - the Megaptera + Balaenoptera clade, if you will. These two modern genera have been traditionally grouped into the "Megapterinae" and "Balaenopterinae" - Zeigler et al. (1997) even went so far as to name a new subfamily, the Parabalaenopterinae. However, given that none of these subfamilies have really shown to be stable or even consistent in cladistic analyses, it's unclear what the utility of such taxon names even is.

 

Reconstruction of the holotype skull and mandibles of Parabalaenoptera. Unfortunately, certain features (e.g. squamosal morphology) of the actual skull don't really look like how they're portrayed in this figure. From Zeigler et al. (1997).

Nevertheless, the description of Parabalaenoptera was a hallmark in balaenopterid paleontology; however, given the stagnated taxonomic situation of fossil balaenopterids, little else was published on fossil balaenopterids until Michelangelo Bisconti started revisiting Italian fossils starting in 2007. In the last five years, a number of informative balaenopterid finds have been described - but it is only the tip of the iceberg. Perusing late Miocene and Pliocene marine mammal assemblages in Museums, it is apparent that balaenopterids comprise nearly two-thirds of the more recent baleen whale fossil record (it is at least the case for California marine mammal assemblages). In California, at least four to five unpublished balaenopterids await description from the Pliocene alone. Additional fossils that may represent Parabalaenoptera - potentially a new and slightly younger species - have been collected from the Purisima Formation near Santa Cruz (and are in much better condition than the holotype). The future of balaenopterid paleontology is bright!

References

Bosselaers, M., and Post, K. 2010. — A new fossil rorqual (Mammalia, Cetacea, Balaenopteridae) from the Early Pliocene of the North Sea, with a review of the rorqual species described by Owen and Van Beneden. Geodiversitas 32:331-363. 

Deméré, T. A., Berta, A., and McGowen, M. R. 2005. — The taxonomic and evolutionary history of modern balaenopteroid mysticetes. Journal of Mammalian Evolution 12:99-143.


Domning, D. P. 1978. — Sirenian evolution in the North Pacific Ocean. University of California Publications in Geological Sciences 18:1-176.


Zeigler, C. V., Chan, G. L., and Barnes, L. G. 1997. — A new late Miocene balaenopterid whale (Cetacea: Mysticeti), Parabalaenoptera baulinensis, (new genus and species) from the Santa Cruz Mudstone, Point Reyes Peninsula, California. Proceedings of the California Academy of Sciences 50(4):115-138.