In The Field

Burgess Shale Centenary: What’s this, then?

If you can’t tell the difference between an embryo and a giant bacterium, then things have got to be pretty bad. But Frank Corsetti of the University of Southern California, Los Angeles, gave the audience a persuasive argument today that at least some spherical bodies found in the fossil record, thought to be eggs or embryos, are indeed probably giant sulphur bacteria instead. Certainly I can’t tell the difference from the pictures, and nor, apparently, can the experts.

These particular fossils are not from the Burgess Shale, nor even from the Cambrian, but from the Neoproterozoic Doushantuo Formation in China, which holds fossils from some 600 million years ago. Not only do some spherical blobs in this record look a lot like a modern sulphur bacterium called Thiomargarita, but this little bug is also known to spit out phosphate, which is required for the particular kind of fossilization found in this formation. Coincidence? Corsetti thinks not.

This kind of confusion about what the heck a fossil represents – plant or animal, whole animal or part of one, egg or bacterium – is rampant throughout paleontology. Peoples’ notions of what they expect to find can deeply influence their description of morphology and identification of fossils, notes famous Yale paleontologist Derek Briggs over lunch. I comment that what you need is a kind of blind experiment, whereby naïve graduate students who know nothing about the subject are asked to describe the morphology of some new fossil. “That is, actually, what happens,” is the witty rejoinder (not, it has to be said, with noble intentions, but by happy accident as a result of students not doing their homework). Seriously, Briggs notes, it would be interesting to see what would happen if scientists could approach fossils without any baggage. That’s a difficult experiment to conduct. Instead of facing such challenges, we go for dessert.

Posted on behalf of Nicola Jones


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