It’s life, Jim, but not as we know it!

A bit belatedly, but as the Cambrian mammal, I feel it’s my duty to jump on the Siphusauctum bandwagon. I was actually a bit surprised by how much news and blog coverage the creature got. I didn’t expect something with no clear affinities to anything and no particularly “cool” features of its own to make many headlines. It’s just a peaceful filter-feeder that looks like a mutant tulip, FFS.

Guess I fail the internet?

Below is a nice bouquet of tul… I mean, Siphusauctum fossils on their slab of rock, from O’Brien and Caron, 2012. They are completely soft-bodied creatures that range from under 2 cm to more than 20 in total height. Presumably, the live animals stood upright on their thin stalks and filtered food particles from the water. The authors speculate that they may have been able to move from one spot to the other, because the small holdfasts at the end of the stalk don’t seem like strong, permanent anchors.

I don’t particularly want to dwell on the details of the paper. It’s the dry and tedious sort of thing descriptions of new taxa usually are, and all those news and blog articles probably beat me to all the basics as far as explaining the animal to a lay audience goes. I just want to make a couple of totally random observations.

One – how the hell do they know that the creature had a mouth? The authors seem quite certain that the digestive tract of Siphusauctum had both a mouth and an anus, but as far as I can tell, they only actually found one hole (which they interpreted as the anus). The mouth is only mentioned a few times, and the most information you get about it is this:

The precise position of the mouth is unknown but was presumably located around the area between the base of the comb-like segments and the stomach. (p16 in the PDF)


and this:

Food particles would have circulated down towards the gut, through a central mouth which has not been identified, but is suggested by the concentration of organic matter in this area. (p18)

Someone please explain why that implies a separate mouth? I mean, they found well over a thousand specimens of not too bad quality. These people have a few thousand times more expertise than me in interpreting weird Cambrian fossils. I would assume they didn’t pull the idea out of thin air, but they don’t exactly make it convincing for non-specialists there 😦 (Not that a single-opening digestive tract makes the animal any easier to interpret…)

TwoSiphusauctum apparently has sixfold symmetry. I don’t know if that’s significant, it just struck me as something that isn’t terribly common in living bilaterians. Hard corals and sea anemones work in multiples of six, but they aren’t bilaterians. But maybe I should go check a zoology textbook…

Three – I found it funny that in true Cambrian style, the creature most similar to Siphusauctum is… Dinomischus? Which is another weird Burgess Shale fossil no one can really place. Well, at least now they have company in being complete riddles. 😀

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