|A flotilla of giant jellyfish marooned on a
beach 500 million years ago has been unearthed in what is now central
Wisconsin. This is the largest-ever find of the biggest-ever fossil jellyfish,
making this an almost impossible find. Since jellyfish are blobs or gel
with no bones or scales, they fossilize poorly. Waves, sand and sun destroy
their bodies before they can be covered in sediment.
"It's rare to find a single jellyfish fossil; to find a lot of them is almost unheard of," says James Hagadorn of the California Institute of Technology in Pasadena, who found the thousands of "hulking huge" jellyfish.
Schools of creatures up to 27.5" (70 cm) long were somehow stranded and buried, probably trapped in a shallow tidal lagoon. Bacteria in the sediments would have consumed the gelatinous flesh, replacing it with minerals.
It's a spectacular find," says paleontologist Ronald Pickerill of the University of New Brunswick in Canada. More so, he adds, because the hapless jellies are found in several different layers of fossilized beach. "It's not just a one-off event, it happened at least six times."
There are fossilized shorelines from the same period worldwide, so Hagadorn hopes that hordes of other fossilized jellies await discovery. From the size and shape of ripples on the sand of the preserved beach, the best guess is that they were trapped in a storm and inadvertently preserved themselves by digging into the sand trying to escape.
Today, stranded jellies are gobbled up by birds and beach-dwelling crustaceans before they could fossilize. During the late Cambrian period, animals didn't yet to colonize land so there were no terrestrial scavengers.
Like many modern-day jellyfish, these fossilized varmints were probably carnivores. Until now there was evidence of only one other similarly sized meat-eater at the time - a meter-long arthropod. The number of individuals in this find indicate they were quite common.