Snotworms For Dinner

Deep in the sea, on the denuded carcasses of whales, there live humble little scavengers. They’re the snotworms, better known to researchers as various species of the polychaete worm Osedax. They pursue a very dedicated lifestyle. Female snotworm larvae settle onto the exposed bones of dead whales, sending down “roots” to tap into the fatty substances locked in the cetacean’s skeleton. Together with mats of bacteria and other organisms, they’re part of a whale deconstruction crew that can totally break down the world’s largest animals.

And the snotworms have been at this for quite some time. Their distinctive pockmarks have been found on fossil whale bones dating back to about 30 million years ago. And even though they’re most famous for feeding on decaying whales, the snotworms can be food, too. In a new Lethaia paper, University of Otago paleontologists Robert Boessenecker and Ewan Fordyce describe divots and scratches on a 28-23 million year old whale that show fish and sharks gobbled snotworms.

The whale in question – of an as-yet-unnamed prehistoric genus and species – was found on New Zealand’s South Island. There was quite a bit of the mammal in the rock, including the skull, vertebrae down to the torso, ribs, and additional bones left at the site. And upon those prehistoric bones are trace fossils that testify to the presence of other organisms. Among the most numerous are clusters of small circular holes that are concentrated on well-preserved bone – these are the signs of prehistoric Osedax, the first fossil occurrence from the southern hemisphere.

Scrape marks - black arrows - around bone damage caused by Osedax worms. From Boessenecker and Fordyce, 2014.
Fish tooth-scrape marks – black arrows – around bone damage caused by Osedax worms. From Boessenecker and Fordyce, 2014.

But in some spots there are other marks that cut across the snotworm holes. The snotworm burrows on the skull bones are associated with shallow, parallel scrape marks. The most likely culprits, Boessenecker and Fordyce propose, are fish and sharks that dragged their jaws across the whale carcass to snaffle the snotworms, roots and all.

The Osedax feast continues today. Boessenecker and Fordyce point out that ratfish and crabs have been seen eating whale bone covered in snotworms, too. As long as there have been snotworms, other creatures have turned to them for food. It’s another indication that, rather than being silent undersea tombs, whalefalls are sites of vibrant life.

Reference:

Boessenecker, R., Fordyce, E. 2014. Trace fossil evidence of predation upon bone-eating worms on a baleen whale skeleton from the Oligocene of New Zealand. Lethaia. doi: 10.1111/let.12108

8 thoughts on “Snotworms For Dinner

  1. Isn’t it equally likely that the tooth marks were from fish or sharks scraping meat off the bones, and that the snotworms then colonised that area of bare bone ?

    Has anyone ever found snotworm holes in the fossils of large marine reptiles ? – that would push their origin back a lot further.

  2. This is amusing to me because I think “snotworm” was added as a name by some screenwriters for the TV show Bones because they wanted to spice up the lay term (which then at some point made it into the wikipedia). Don’t think any researchers actually use that word in the field, even casually. My source is knowing someone who graduated from the lab that made Osedax famous and talking about this before with her. Anyway, you might want to email Greg Rouse at SIO to figure out if anyone actually calls them snotworms 🙂

  3. No. While there are some tooth marks that appear on non-bioeroded surfaces (e.g. parallel set in fig D above) the tooth marks implicated as being formed during predation on Osedax actually occur within and conform to the surface of the bioeroded galleries – in other words, a gallery was already present when the tooth mark was formed. In these regions, the cortex is totally absent (where surficial tooth marks would have existed). In Fig. C above, a parallel set of toothmarks occurs within a ~5mm deep, ~15mm wide pockmark – this surface was not exposed prior to it being formed by an Osedax worm.

    Regarding marine reptiles, also no – marine reptile deadfalls have been identified, but none yet bear traces of Osedax bioerosion. The oldest records of Osedax bioerosion still appear to be Oligocene in age, although I believe I have seen Eocene archaeocete remains with pockmarks, the most readily identifiable style of trace left by Osedax.

  4. Thanks

    Is there any difference between whale and marine reptile bones that would make whale bones a better resource for burrowing scavengers ? – it seems odd otherwise that snotworms (or their predecessors) did not exploit reptile carcasses.

  5. Excellent question. The short answer is we don’t know. We don’t really actually know what modern Osedax actually targets, and there is a debate going on whether or not it targets lipids in the marrow cavity or if it targets collagen; Nick Higgs has made a robust case (in my opinion) for the latter, which would suggest a wide variety of suitable skeletal substrates. That being said, Osedax has been known to experimentally colonize cow bones and fish bones and Oligocene fossils indicate that it also colonized bird bones and whale teeth in the past – which confirms that Osedax can colonize a wide variety of taxa (fish, birds, mammals) and tissue types (mammalian bone, avascular bone, and dentine). In sum, everything points towards Osedax being capable of colonizing late K marine reptiles. Perhaps the traces just haven’t been found yet – it takes good preservation to find the traces, and better preparation (they are really challenging to prepare owing to paper thin jagged bone edges). However, it’s also possible that Osedax did not evolve until the late Paleogene: the two available molecular clock divergence dates are the Cretaceous and sometime in the Eocene or Oligocene – if after another decade of intensive searching we have no Cretaceous Osedax traces, I’d tend to side with a younger origin for bone eating worms.

    1. Intriguing – presumably something was eating reptile bone, or the sea floor would be carpeted with icthyosaurs ! What about sea-floor chemistry I wonder.

  6. Another good question – as it happens, most marine reptile skeletons that have been reported in the literature appear to generally lack the extensive sorts of bioerosion associated with Osedax. In the Oligocene of NZ, something like half of all associated skeletons have bones reduced to strange splinter shapes where 3/4 of the bone volume has been bioeroded away. Available taphonomic studies suggest only minor (e.g. superficial) bioerosion of marine reptile bones. So it’s possible that the niche didn’t really exist before Osedax – but again, these worms have only been formally known about for a decade, and people only started looking for fossil traces of them about five years ago.

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