Fossilized chain formations reveal community behavior
The discovery of 525-million-year-old fossils belonging to a new species of arthropod shows that these animals formed communal chains never before seen in fossilized invertebrates, scientists report in the Oct. 10 Science.
These arthropods, a phylum that includes lobsters, beetles and tarantulas, were
found in sturdy chain configurations in southern
Nigel Hughes, a paleobiologist from the
“Of the millions of fossils, the chances of getting an
occurrence where we can determine collective behavior is quite rare,” says
coauthor Derek Siveter of the
“As far as I know, the group behavior exhibited by these
fossils is nearly unknown in modern invertebrates, and has never been
demonstrated in fossil invertebrates,” says geobiologist Anthony Martin of
Modern-day animals are known to display collective behavior.
Siveter points to spiny lobsters in the
Based on the twists and turns of these fossilized chains, Siveter and his colleagues postulate that the chains may have floated in the early Cambrian ocean.
But the researchers still don’t know why these arthropods linked themselves together. Feeding behavior is an unlikely reason since each individual’s mouth is covered by the tail of the preceding arthropod. And it is also unlikely that being in a chain made it easier to reproduce. Because other types of fossilized arthropods were known to migrate, the scientists’ best guess is that these chains may have provided members protection against predators while on a long migration — in other words, strength in numbers.
“When you’re dealing with 525-million-year–old animals, it’s not like math where five plus five is ten. There are a lot of interesting discussions to have,” explains Siveter.
The purpose of these chains is something scientists will puzzle over for a long time, but one thing is clear: These ancient animals did not act alone.
“This find provides extraordinary insights into the early evolution of group behaviors, possibly representing a combination of reproductive and anti-predatory strategies,” says Martin. “In short, this find should cause all who are interested in fossil behavior to reconsider what we know about group behavior.”
Hou, Xian-Guang et al. "Collective Behavior in an Early Cambrian Arthropod," Science, 10 October, 2008. Vol. 322.
Sid Perkins, “Fossil confirms that early arthropods molted,” Science News, May 15th, 2004; Vol.165 #20 (p. 318)