Report: 500-million-year-old monster predator not a little "crab"

2009-03-20

WASHINGTON, March 19 (Xinhua) -- Hurdia victoria, originally described as a crustacean-like animal, is now described as a 20-cm-long giant, during whose time most creatures were no bigger than a fingernail, researchers reported in Thursday's peer-reviewed journal Science.

The study says that Hurdia is the early offshoot of the evolutionary lineage that led to the arthropods, the large modern group that contains the insects, crustaceans, spiders, millipedes and centipedes.

A team of scientists from Sweden, Canada and Britain assembled fragments of fossils to expose a "lie" -- Hurdia would have been a crab like crustacean animal, by saying it would be a formidable predator.

The first fragments of the Hurdia fossils were found nearly 100years ago at the famous 505-million-year-old Burgess Shale, a UNESCO World Heritage Site in British Columbia, Canada. They were then assumed to be part of a crustacean-like animal.

Fragments of fossils were continuously excavated, but they were independently described as jellyfish, sea cucumbers and other arthropods, and were not realized as parts to one animal.

However, collecting expeditions in the 1990s uncovered more complete specimens and hundreds of isolated pieces that led to the first hints that Hurdia was more than it seemed.

With researches advancing, Hurdia is now described as an arthropod having a segmented body with a head bearing a pair of spinous claws, a circular jaw structure with many teeth and a huge three-part carapace that projects out from the front of the animal's head.

"This structure is unlike anything seen in other fossils or living arthropods," says Ph. D. student Allison Daley, who has been studying the fossils for three years as part of her doctoral thesis.

"The use of the large carapace extending from the front of its head is a mystery. In many animals, a shell or carapace is used to protect the soft-parts of the body, as you would see in a crab or lobster, but this structure in Hurdia is empty and does not cover or protect the rest of the body. We can only guess what its function might have been," says Daley.

Scientists also say that Hurdia reveals details of the origins of important features that define the modern arthropods such as their head structures and limbs. As well as its bizarre frontal carapace, Hurdia reveals exquisite details of the gills associated with the body, some of the best preserved in the fossil record.

"Most of the body is covered in the gills, which were probably necessary to provide oxygen to such a large, actively swimming animal," says Daley.