Fossil fragments have been pieced together to reveal the true identity of a 500-million-year-old monster predator, scientists report in the journal Science today.
This new discovery sheds light on the origin of the largest group of living animals, the arthropods – a group that includes insects, crustaceans, spiders, millipedes and centipedes.
The fragments of fossils were previously thought to belong to various creatures such as a jellyfish, a sea cucumber and a crustacean-like animal. But scientists at the Natural History Museum, UK, Uppsala University, Sweden, and the Royal Ontario Museum, Canada, decided to take a closer look.
They studied old and newly found fossils and came up with the new description of the marine predator, Hurdia victoria, a creature that lived alongside early arthropods.
Hurdia victoria was a large animal, especially compared to other arthropods. There are complete fossil specimens that are 20cm long but pieces of broken specimens suggest it was possibly up to 50cm in length.
It had big eyes, a segmented body, a head with a pair of spiny claws and a circular jaw structure with many teeth.
It would have been a formidable predator in the seas and may have fed on trilobites (extinct marine arthropods) and other arthropods on the sea floor.
Hurdia had a unique, large 3-part shell that projected out from the front of the animal’s head.
‘It was hard to tell whether the box-like shell structure came to lie so far forward after the animal died, or when it moulted its hard parts, or if this was how it really looked when alive,' says Greg Edgecombe, fossil expert (palaeontologist) at the Natural History Museum.
'The way the fossil is preserved made us decide that it really had this structure in front of its head, but we still don’t know what it was for.’
The fossils were from the famous Burgess Shale deposits of the Canadian Rockies, a UNESCO World Heritage Site.
Many exceptionally well-preserved fossils have been uncovered there and they present a remarkable snapshot of Cambrian marine life from 505 million years ago.
The first fragments of Hurdia victoria were described nearly 100 years ago and were assumed to be part of other animals.
More clues to the real nature of Hurdia accumulated over the years as new specimens were collected or discovered in museum collections.
The last piece of the puzzle was found when the best-preserved specimen was discovered in the collections at the Smithsonian National Museum of Natural History in Washington DC.
Illustration of Anomalocaris, a relation to the new marine predator Hurdia victoria
It was collected by Charles Walcott in the early 20th century. This specimen lay untouched for decades until researchers in the 1970s and 80s classified it first as an arthropod and then as an unusual specimen of the famous monster predator Anomalocaris.
The new description of Hurdia shows that it is indeed related to Anomalocaris. They are both early offshoots of the evolutionary lineage that led to the arthropods.
Hurdia fossil showing detail of gills just above one of the front claws
Hurdia and Anomalocaris reveal details of the origins of important features that define the modern arthropods. They both show compound eyes and also limb flaps with gill filaments used for breathing.
As well as its bizarre head structures, the fossilised Hurdia victoria reveals exquisite details of the gills associated with the body, some of the best preserved in the fossil record.