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.