Paleontologists have uncovered a fossil species — named Tokummia katalepsis — that sheds light on the origin of Mandibulata (mandibulates), the most diverse and abundant group of animals, to which belong flies, ants, crayfish and centipedes.

Tokummia katalepsis — a large bivalved arthropod from the Marble Canyon fossil deposit, Burgess Shale, British Columbia, Canada — documents for the first time in detail the anatomy of early mandibulates.

“In spite of their colossal diversity today, the origin of mandibulates had largely remained a mystery,” said Dr. Cédric Aria, a postdoctoral researcher at the Nanjing Institute for Geology and Palaeontology, China, and the lead author of a report published this week on Tokummia katalepsis in the journal Nature.

“Before now we’ve had only sparse hints at what the first arthropods with mandibles could have looked like, and no idea of what could have been the other key characteristics that triggered the unrivaled diversification of that group.”

Tokummia katalepsis lived in tropical seas during the Cambrian period, approximately 508 million years ago.

This creature was a bottom-dweller, as lobsters or mantis shrimps today, and was among the largest predators of its time, exceeding 3 inches (10 cm) in length.

“This spectacular new predator, one of the largest and best preserved soft-bodied arthropods from Marble Canyon, joins the ranks of many unusual marine creatures that lived during the Cambrian Explosion, a period of rapid evolutionary change starting about half a billion years ago when most major animal groups first emerged in the fossil record,” said co-author Dr. Jean-Bernard Caron, senior curator of invertebrate paleontology at the Royal Ontario Museum and an associate professor at the University of Toronto.

Analysis of several fossil specimens, following careful mechanical preparation and photographic work, showed that Tokummia katalepsis sported broad serrated mandibles as well as large but specialized anterior claws (maxillipeds), which are typical features of modern mandibulates.

“The pincers of Tokummia katalepsis are large, yet also delicate and complex, reminding us of the shape of a can opener, with their couple of terminal teeth on one claw, and the other claw being curved towards them,” Dr. Aria said.

“But we think they might have been too fragile to be handling shelly animals, and might have been better adapted to the capture of sizable soft prey items, perhaps hiding away in mud.”

“Once torn apart by the spiny limb bases under the trunk, the mandibles would have served as a revolutionary tool to cut the flesh into small, easily digestible pieces.”

The body of Tokummia katalepsis is made of more than 50 small segments covered by a broad two-piece shell-like structure called a bivalved carapace.

Importantly, the animal bears subdivided limb bases with tiny projections called endites, which can be found in the larvae of certain crustaceans and are now thought to have been critical innovations for the evolution of the various legs of mandibulates, and even for the mandibles themselves.

The many-segmented body is otherwise reminiscent of myriapods, a group that includes centipedes, millipedes, and their relatives.

“Tokummia katalepsis also lacks the typical second antenna found in crustaceans, which illustrates a very surprising convergence with such terrestrial mandibulates,” Dr. Aria said.

The study also resolves the affinities of other emblematic fossils from Burgess Shale more than a hundred years after their discovery.

“Our study suggests that a number of other Burgess Shale fossils such as Branchiocaris, Canadaspis and Odaraia form with Tokummia katalepsis a group of crustacean-like arthropods that we can now place at the base of all mandibulates,” Dr. Aria said.

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Cédric Aria & Jean-Bernard Caron. Burgess Shale fossils illustrate the origin of the mandibulate body plan. Nature, published online April 26, 2017; doi: 10.1038/nature22080