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life in the cambrian

I first read Stephen Jay Gould's book, Wonderful Life, not long after it was first published in 1989. The book centres on the Burgess Shale, a wonderfully rich source of of different fossils (a Lagerstätte) from the Cambrian, around 530 million years ago. The Burgess Shale is unusual in that it contains an array of soft-bodied organisms, as well as those with shells and exoskeletons - & they are exquisitely preserved in 3-D detail. The book gives a sense of the excitement that scientists felt as they extracted these fossils from their rocky matrix and realised what they were dealing with.

Many of the Burgess Shale fossils are from arthropods - animals with a an exoskeleton & jointed legs. One of these is called Waptia - it looks vaguely like a shrimp. Now I see from PZ Myers, over on Pharyngula, that researchers studying the Chengjiang Lagerstätte, in China, have found some most unusual fossils of a Waptia-like creature - they're joined together, head to tail, like beads on a strange necklace. The paper's authors suggest that this may represent feeding behaviour, but this sounds a bit odd. As PZ says, the animals are joined nose-to-tail, so the last one in the chain is going to be getting a very unsavoury meal indeed!

waptia.jpg
(Click for larger image)

Waptia-like arthropod, Lower Cambrian, Haikou, Yunnan. (A) Individual with twisted abdomen, part of chain, Yunnan Key Laboratory for Palaeontology, YKLP 11020a. (B) Chain, about 20 individuals, various dorsoventral-lateral orientations, composite image (joined at cpt/p arrow), YKLP 11020a and YKLP 11020b. (C) Individual linked to carapace behind, lateral view, part of chain of nine individuals, YKLP 11021. (D) Isolated individual, subventral view, YKLP 11019. (E to G) Reconstruction shown in dorsal, ventral, and right lateral views, respectively. Scale bars in (A), (C), and (D) indicate 1 mm; in (B) and (E) to (G), 5 mm. b, s, and t indicate bent, stretched, and telescoped individuals, respectively; cpt, counterpart; f, facing direction; p, part; and tw, twisted. (from Pharyngula - original image is in Hou X-G, Siveter DJ, Aldridge RJ, Siveter DJ (2008) Collective Behavior in an Early Cambrian Arthropod. Science 322(5899):224.

 

 

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I read Wonderful Life around roughly the same time. I think from memory the first chapter, or at least one early chapter was a one-chapter take on the punctuated equilibrium model. While you can argue about its merits, it seemed a startling idea at the time.

Those head-to-tail arthropods are crazy little guys! Some of the comments suggest that they might be migrating "as a team" as it were. Apparently lobsters do something vaguely like this. I thought for a giggle of tossing in the fanciful idea of them being the solid-body remains of unhatched individuals in an elongated chain of soft-bodied eggs, to see if it'd spark a spin-off in the thread, but they'd have to be immature in that case and I didn't have time to read the paper to see if it was even remotely plausible. Of course I know nothing about the biology of these things! :-)

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