Fragments of the creature were unearthed in 1912 in Canada’s 505 million-year-old Burgess Shale site, but scientists initially thought they were part of a crustacean-like animal.
It was not until the discovery of better specimens in the 1990’s that they realised fossils previously classified as jellyfish, sea cucumbers and other anthropods were actually pieces of an entirely new beast.
Called the Hurdia victoria, it 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 journal Science.
“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.
“The use of the large carapace extending from the front of its head is a mystery. In many animals, the shell 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,” she said.
The specimen discovered in the Smithsonian’s collection was first 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 US were able to reclassify it after studying several 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 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.
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