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terror of the ancient seas?

Blogging on Peer-Reviewed Research I was first introduced to the wonders of the Burgess Shale by reading Steven Jay Gould's book, Wonderful Life. And I was hooked - fascinated by the weird beauty of many of those Cambrian organisms. The one that made the greatest impression was Anomalocaris: a predatory animal up to a metre long, with a ring-shaped battery of 'teeth' in its mouth & a couple of great big jointed appendanges ( the 'great appendages') at the front of its head. It really would have been a terrible thing to meet, if you were a smaller, softer creature that looked like lunch.

So when PZ wrote about a relative of Anomalocaris that lived in the Devonian, 100 million years later, of course I had to go off & read the original paper (Kuhl, Briggs & Rust, 2009).

As I said, the Burgess animals were weirdly beautiful, & the new Devonian animal, Schinderhannes bartelsi, is no exception. The fossil's very well-preserved, in enough detail for the research team to draw some conclusions about its relationships. Like AnomalocarisS. bartelsi had a round mouth & paired great appendages on its head, plus large lateral eyes. The great appendages were covered by spines, which suggests that bartelsi  was also a predator. Unlike Anomalocaris, it had strange wing-like structures a little way down from the mouth. ('Wing-like', but definitely not wings - this was a marine animal.) Its segmented body was covered by a series of 12 hardened dorsal plates ('tergites'), & 10 of those segments bore jointed limbs. And those limbs were biramous - meaning that they were divided into two branches: a feature shared with many modern arthropods (but not the insects).

The team concluded that the various physical features of Schinderhannes bartelsi indicate that it's a very early member of a taxon called the Euarthropoda, to which all modern arthropods belong. They go further, suggesting that the 'great appendages' seen in bartelsi aren't lost in modern arthropods, but exist in highly modified form as the fangs, or chelicerae, of modern spiders.

But, well-armed & well-armoured as it was, Schinderhannes was unlikely to have been the terror of the Devonian seas. It was, after all, only 98mm long.

G.Kuhl, D.E.G.Briggs & J. Rust (2009) A great-appendage arthropod with a radial mouth from the Lower Devonian Hunsruck Slate, Germany. Science 323: 771-773

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Very cool. And I love the way new fossil discoveries are helping to put the Burgess Shale animals into a phylogenetic context. It rather dilutes Gould's assertions about the huge disparity in body plans back in the Cambrian, but it makes a lot of evolutionary sense.

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