Evrim Yazgin
Cosmos science journalist
A taco-shaped arthropod – or “tacopod” as I shall affectionately refer to it henceforth – which has long eluded classification has finally been identified as one of the first creatures to have mandibles.
The tacopod is actually called Odaraia alata. It was about 15cm long and lived during the middle of the Cambrian period (541–485 million years ago).
It had large eyes and glands, indicating it was an active hunter.
Odaraia fossils have been found for more than 100 years at the Burgess Shale in Canada, the site which first introduced to the world the massive burst of life which took place more than 500 million years ago known as the “Cambrian explosion.”
The Cambrian explosion saw the emergence of all the basic body shapes seen in animals today.
Among these are the exoskeletal arthropods, the descendants of which today include insects, spiders, crabs and millipedes. The Cambrian also saw the first eyes, legs and shells.
The new analysis of the tacopod Odaraia, carried out by the Royal Ontario Museum (ROM) in Canada, is published in the Proceedings of the Royal Society B Biological Sciences.
Scientists identified mandibles on Odaraia for the first time. This makes it one of the earliest known members of the mandibulate group of animals. But that’s not all. Analysis of its more than 30 legs showed a complex pattern of small and larger spines. They suggest the spikes could be used to catch smaller prey.
“The head shield of Odaraia envelops practically half of its body including its legs, almost as if it were encased in a tube,” says lead author Alejandro Izquierdo-López, based at ROM during this work as a PhD student at the University of Toronto. “Previous researchers had suggested this shape would have allowed Odaraia to gather its prey, but the capturing mechanism had eluded us, until now.”
“Odaraia had been beautifully described in the 1980s, but given the limited number of fossils at that time and its bizarre shape, two important questions had remained unanswered: is it really a mandibulate? And what was it feeding on?”
Early mandibulates would have migrate from the bottom-dwelling marine ecosystems into the upper layers of the water column. They likely enriched the water column, thereby facilitating the transition into more complex marine ecosystems half a billion years ago.
“Thanks to the work we have been doing at the ROM on amazing fossil animals such as Tokummia and Waptia, we already know a substantial amount about the early evolution of mandibulates,” says co-author says Jean-Bernard Caron, Richard Ivey Curator at ROM.
“However, some other species had remained quite enigmatic, like Odaraia.”
