|Two specimens of the 508 million year old arthropod Yawunik|
kootenayi from the Kootenay National Park, Canada
Instead an elemental map was made of the fossil, an increasingly common form of analysis, which contrasts the fossiliferous material with the matrix based on a differing chemical composition. In this way detail invisible to the naked eye is made visible.
The scans revealed a shrimp-like creature with prominent grasping appendages and a powerful array of sensory antennae, the hallmarks of a predator.
'This creature is expanding our perspective on the anatomy and predatory habits of the first arthropods, ' said Cedric Aria from the University of Toronto. 'It has the signature features of an arthropod with its external skeleton, segmented body and jointed appendages, but lacks certain advanced traits present in groups that survived until the present day. We say that it belongs to the 'stem' of arthropods.'
Given the name of Yawunik kootenayi after a fierce marine creature from the legends of the local Ktunaxa people, it clearly played an important role in the Cambrian ecosystem. 'Unlike insects or crustaceans, Yawunik did not possess additional appendages in the head that were specifically modified to process food,' said Aria.
'Evolution resulted here in a combination of adaptations onto the frontal-most appendage of this creature, maybe because such modifications were easier to acquire. We know that the larvae of certain crustaceans can use their antennae to both swim and gather food. But a large active predator such as a mantis shrimp has its sensory and grasping functions split up between appendages. Yawunik and its relatives tell us about the condition existing before such a division of tasks among parts of the organism took place.'
Despite the lack of specialised limbs, numerous fossils show that Yawunik held a key position in the local food web. Its precise ecological relationships have yet to be reconstructed. The Kootenay site is a recent find, and while a plethora of new species have been named, it will take time to understand how they interacted with one another. Nevertheless, it offers exciting research opportunities into the Cambrian Explosion.