Fossils of an ancient, lobster-like creature that is the forerunner of a diverse group of creatures including lobsters, butterflies, and spiders have been identified by paleontologists at the University of Toronto, the Royal Ontario Museum, and Pomona College in California.
The species, Yawunik kootenayi, is described as a marine predator that had two pairs of eyes and prominent frontal appendages that could have been used for grasping. They believe that it lived more than 508 million years ago, or 250 million years before the first dinosaurs.
Yawunik kootenayi is believed to be the first new species to be described from Toronto’s Marble Canyon site, part of the renowned Canadian Burgess Shale fossil deposit, the researchers said. A paper describing the discovery was published this week in the journal Palaeontology.
The frontal appendages of the creature are said to resemble those found on modern-day shrimp or beetles, but they were actually made up of three long claws, two of which had opposing rows of teeth that could be used by the creature to make sure its prey did not get away.
“This creature is expanding our perspective on the anatomy and predatory habits of the first arthropods, the group to which spiders and lobsters belong,” said lead author Cedric Aria, a Ph. D. candidate in the University of Toronto Department of Ecology and Evolutionary Biology.
“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,” he added.
Versatile and complex appendages
Aria and his colleagues found evidence indicating that Yawunik was able to move forwards and backwards using those frontal appendages, and could also spread them out when attacking and retract them beneath its body when swimming. When combined with the long, sensing whip-like flagella extending from the claw tips, it meant that the creature’s front appendages were some of the most versatile and most complex ever seen in an arthropod species.
“Unlike insects or crustaceans, Yawunik did not possess additional appendages in the head that were specifically modified to process food,” Aria explained. “Evolution resulted here in a combination of adaptations onto the frontal-most appendage of this creature, maybe because such modifications were easier to acquire.”
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“We know that the larvae of certain crustaceans can use their antennae to both swim and gather food,” he added. “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.”
“Yawunik is the most abundant of the large new species of the Marble Canyon site, and so, as a predator, it held a key position in the food network and had an important impact on this past ecosystem,” said Caron, a co-author on the study. “This animal… shows how the site increases the significance of the Burgess Shale in understanding the dawn of animals.”