Aug. 10, 2006 — Trilobites, the extinct marine creatures famous to fossil-hunters everywhere, may have once done digging of their own, say British and Swedish researchers.
Rocks found in a Swedish limestone quarry contain the remains of trilobites inside networks of tunnels, which appear to have been subsurface thoroughfares for the little bug-like critters.
"It’s very rare to find a trilobite in a burrow," said Amherst College paleontologist Whitey Hagadorn, an expert on tracks, burrows and other “trace” fossils that can give important clues to a long-lost species’ behavior and environment.
In fact there's only one other such fossil known, said Hagadorn, and even that one doesn’t show evidence that the tunnels were much more than single-use, one-way streets that collapsed after the animals made their way through the muck.
"The fact that they form open networks, that is new and different," said Hagadorn.
Such sand-filled tunnels are common in the fossil record, said Hagadorn, and have generally been attributed to soft-bodied animals that left behind no hard parts. But in recent years, paleontologists have begun to suspect that trilobites may have done some digging as well.
Finding trilobites inside tunnel remains in Sweden's 465-million-year-old Holen Limestone is, therefore, a fitting but unexpected hint about how the ubiquitous creatures fit into the Paleozoic ocean ecosystem.
As for how these particular fossils were found, it was an accident, said Lesley Cherns of Cardiff University.
"We sat down to lunch and I noticed that there were trilobites in these burrows," said Cherns, who co-authored a paper in this month's issue of Geology on the discovery.
The trilobites were probably killed by something like a sudden upwelling of oxygen-poor water or some other quick and deadly event. The tunnels were soon thereafter buried by a thick layer of mud that sealed them off from scavengers and helped preserve the evidence, Cherns explained.
As for what the trilobites were doing underground, no one is quite sure. They could have been hiding from the nautilus-like predators that cruised the Paleozoic oceans, said Cherns. Or they may have used the water flowing through the tunnels to help oxygenate their gills, like some modern lobsters do, she said.
"They could have been going down to eat, reproduce, hide… who knows?" said Hagadorn. "Hopefully this will motivate people to go out and look for more of these."
That could eventually answer some of those questions, he said.
