When Trilobites Ruled the World ; Diverse Marine Animals, Extremely Well-Preserved Fossils, Hold Surprises
Angier, Natalie, International New York Times
The remains of trilobites, a diverse group of marine animals much older than dinosaurs, are remarkably well preserved, providing fresh insights of their anatomies and social behavior.
Trilobites may be the archetypal fossils, symbols of an archaic world long swept beneath the ruthless road grader of time. But we should all look so jaunty after half a billion years.
At the Smithsonian's National Museum of Natural History, Brian T. Huber, chairman of paleobiology, points to a flawless specimen of Walliserops, a five-inch trilobite that swam the Devonian seas around what is now Morocco about 150 million years before the first dinosaurs hatched. With its elongated, triple-tined head horn and a bristle brush of spines encircling its lower body, the trilobite could be a kitchen utensil for Salvador Dali. Nearby is the even older Boedaspis ensifer, its festive nimbus of spiny streamers pointing every which way like the ribbons of a Chinese dancer.
In a back room of the museum, Mr. Huber opens a drawer to reveal a dark, mouse-sized and meticulously armored trilobite that has yet to be identified and that strains up from its sedimentary bed as though determined to break free.
"A lot of people, when they see these fossils, don't believe they're real," said Mr. Huber, 54. He is fit from years of fieldwork and proud that the state fossil of his native Ohio is a trilobite. "They think they must be artists' models."
The fossils are real, and so, too, is scientists' unshakable passion for trilobites, a diverse and illuminating group of marine animals that once dominated their environment as much as dinosaurs and humans would later dominate theirs -- and that still stash a few surprises up their jointed sleeves.
In a series of reports, scientists have described fresh insights into the trilobite's crystal-eyed visual system, unique in the animal kingdom, and its distinctive body plan, a hashtag of horizontal segments arrayed along three vertical lobes that allowed the trilobite to roll up into a defensive ball against predators and sea squalls.
Other researchers have found evidence that some trilobites were highly social, migrating long distances in a head-to-tail procession as they searched for food, or gathering together during molting season at a kind of Trilo's Retreat, where they could simultaneously shuck off their carapaces and seek out mates.
"It looks like a lot of trilobite mating behavior happened when they were in a soft-shelled form," said Carlton E. Brett, a professor of geology at the University of Cincinnati, who has presented research on trilobite assemblages to the Geological Society of America and elsewhere. "They did it in the nude."
To investigate trilobite social life, Mr. Brett and his colleagues analyzed numerous examples of mass burial sites, where congregations of trilobites had been trapped in place by the sedimentary upheavals from violent sea storms, just as the citizens of Pompeii were smothered by Vesuvian ash. "You feel a little bad for the trilobites, but it's incredible seeing these things preserved in the act of life processes," Mr. Brett said. "It's frozen behavior."
On a similarly erotic note, some researchers have proposed that many of the more gothic features identified in the trilobite fossil record -- the oversized head horns, the curlicue shoulder spines and maybe the eyestalks that look like a couple of periscopes plunked on either side of a trilobite's face -- are the trilobitic equivalent of a peacock's tail, results of sexual rather than natural selection.
By that argument, the showstoppers in a given collection are probably males, their appurtenances having evolved to impress females or intimidate rival males. "If you look at the diversity of life now, most of the weird, exaggerated things we find are sexually selected," said Robert J. Knell of the University of London. "There's no reason to think evolution was working differently in the past. …