The fossils of the monster predator show it has a circular jaw and a pair of claws on its head and were discovered in the old collections of the Smithsonian museum in Washington, researchers said on Thursday.
“This structure is unlike anything seen in other fossil or living arthropods,” said lead author Allison Daley, who has been studying the fossils for three years as part of her doctoral thesis at Uppsala University in Sweden.
Fragments of the creature were unearthed in 1912 in Canada’s 505 million-year-old Burgess Shale site but researchers initially thought they were part of a crustacean-like animal.
It was not until researchers discovered more complete specimens in the 1990’s that they realized fossils previously classified as jellyfish, sea cucumbers and other anthropods were actually pieces of an entirely new beast.
Hurdia victoria has a segmented body covered with gills and a huge three-part carapace, or shell, that projects out from the front of its head, according to the study published in the peer-reviewed journal Science.
“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 at what its function might have been.”
The specimen discovered in the Smithsonian’s collection was classified as an anthropod in the 1980’s and then as an unusual specimen of the predator Anomalocaris.
But Daley and a team of researchers from Canada, Britain and the United States were able to reclassify it after studying several hundred specimens recovered from the Burgess Shale.
Hurdia and Anomalocaris are both early offshoots of the evolutionary lineage that led to arthropods, a large modern group that contains spiders, crustaceans, insects, millipedes and centipedes.
The fossils reveal details of the origins of important features that define the modern arthropods such as their limbs and head structures.
The Hurdia specimens reveal exquisite details of its gills, 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,” Daley said.