Washington, March 17 : Researchers have discovered an entire population of trilobites fossilized during orgy. These ancient arthropods - relatives of lobsters, spiders and insects - went extinct more than 250 million years ago.

Carlton E. Brett, University of Cincinnati professor of geology, found evidence for ancient environment and behavior in these mass graves.

This cluster of Devonian trilobites suggests a mass gathering for molting and mating, said Brett.

In a quest that has taken him from Oklahoma to Morocco and Poland, Brett has analyzed multiple examples of mass trilobite burial. A smothering death by tons of hurricane-generated storm sediment was so rapid that the trilobites are preserved in life position. These geologic "snapshots" record behavior in much the way that ancient Roman life was recorded at Pompeii by volcanic ash.

Burial was rapid, Brett said, but also somewhat delicate. Trilobites, like other arthropods, shed their hard exoskeletons from time to time.

Polish paleontologist Adrian Kin of Poland''s Institute of Geological Sciences at Jagiellonian University, found this chain of trilobites, resembling the migratory queues observed among modern crustaceans.

"We find molted pieces lying immediately adjacent to each other," he said.

"This is proof that the sediments were not significantly disturbed after burial."

Like modern crabs and lobsters, trilobites appear to have gathered in large groups for protection when they shed their protective exoskeletons. During molting, there was safety in numbers. And, like their modern cousins, trilobites seem to have used these molting gatherings as opportunities for mating.

The mass burials preserve large groups of similar-sized - and therefore similarly aged - specimens, segregated by species and, after molting, "naked."

"It''s an orgy," said Brett.

Taken together, the mass burials record an array of communal behaviors in ancient trilobites, comparable to those seen in some living crustaceans.

"Such evidence points to complex synchronized escape and reproductive behavior," said Brett.

"This provides extraordinary insights into the paleobiology of these ancient organisms," added Brett.

The findings will be presented at the Geological Society of America regional meeting in Pittsburgh. (ANI)