Here's a very strange fossil from the Chengjiang Lagerstätte, an early Cambrian fossil bed from 525 million years ago. It's a collection of Waptia-like arthropods, nothing unusual there; these are ancient creatures that look rather like headless shrimp. What's weird about it is the way the individuals are locked together in a daisy chain, with the telson (tail piece) of each individual stuck into the carapace of the animal behind. It's not just a fluke, either — they have 22 fossil chains, and just one animal all by its lonesome.
(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.
They do not look like animals that were constrained in a burrow, or that were crawling over the surface. Rather, they had been swimming together in a chain at death, and the whole chain fell to the sea bed, bending and kinking but still remaining firmly locked together.
Why were they doing this? My first thought was of sex; everyone knows how dragonflies and damselflies lock together for mating, but of course that would predict pairs of individuals, not 20 at a time. It also reminded me of the Drosophila mutant fruitless, in which male flies court other male flies, and they spontaneously form conga lines in the culture bottles. That's also unlikely, since that kind of behavior doesn't lead to a consistent pattern of successful reproduction, but maybe if these animals were hermaphroditic, it might work. It's not a behavior that any modern arthropods show, however.
The authors consider the possibility it is a feeding strategy, but that's even worse: they're locked basically mouth to anus, which would mean the fellow at the end of the line gets a very unpleasant diet. They conclude that the most likely explanation is that this represents a migratory behavior, perhaps involved in daily vertical migration. It may have been that strings of these animals would link up and paddle together to move to new feeding sites, where they separated and dispersed until the time came to move elsewhere.
Hou X-G, Siveter DJ, Aldridge RJ, Siveter DJ (2008) Collective Behavior in an Early Cambrian Arthropod. Science 322(5899):224.
20 Comments
Stanton · 13 October 2008
I would think that this would be either some sort of mating ritual, like the way sea hares link up together in long conga lines during mating season, or, perhaps it was some sort of behavioral migratory ritual, like the way spiny lobsters march single file in the Caribbean.
Would it be possible if we could get access to the original report?
Henry J · 13 October 2008
So it's loosely analogous to what geese do when migrating, with the ones in front reducing the wind resistance for the ones trailing (and they swap places when the leader gets tired).
Henry
Ichthyic · 13 October 2008
Would it be possible if we could get access to the original report?
unfortunately, only if you yourself have a subscription to Science. It's not legal to repost those articles in their entirety. sometimes brief notes get full access, but I don't think so in this case.
Stanton · 14 October 2008
GTM · 14 October 2008
Prepare for Noah's flood comments.
eric · 14 October 2008
The abstract is freely accessible. The link is below, but after reading PZ's summary you will be disappointed (its a lot less detailed).
http://www.sciencemag.org/cgi/content/abstract/322/5899/224
Mark Farmer · 14 October 2008
Reminds me of the behavior of Spiny Lobsters.
Check out the first photo at:
http://www.superstock.com/stock-photography/Panulirus
EoRaptor013 · 14 October 2008
OT
Has anybody seen this NY Times article about drug resistant pneumococcus? Seems doctors have been using a vaccine effective against 7 of 91 types of pneumococci. Two passages in the article pulled me up by the short hairs:
"...experts have worried from the start whether bacteria that were just as deadly, but not wiped out by the vaccine, might move in as opportunists when the competition suddenly vanished." and
"Pneumococci ebb and flow in natural cycles, and some types have gained a survival advantage by growing resistant to a host of drugs. The vaccine may have simply amplified natural trends."
All I can say is, "Doh!" Dem dokters don't need no eviloution. No siree.
KP · 14 October 2008
KP · 14 October 2008
I just realized that OT means "off-topic." Heh heh.
Steve Bodio · 14 October 2008
Don't spiny lobsters form similar chains to migrate?
SWT · 14 October 2008
Alex · 14 October 2008
I think a much more interesting question is, what could possibly make 20 linked individuals all die simultaneously without losing their grip on each other. It's truly fascinating.
Stanton · 14 October 2008
Stanton · 15 October 2008
Also, can I get some feedback about this reconstruction?
http://avancna.deviantart.com/art/Sketch-Chengjiang-Daisychain-100785964
RWard · 15 October 2008
Stanton · 15 October 2008
rward · 17 October 2008
Very nice. May I have permission to use it in a lecture to a freshman class?
I'd like to use it this semester, but if you modify it later I would love to change to the latest version.
It really is impressive. I wish I could do something other than doodle.
Stanton · 17 October 2008
Stanton · 5 December 2008