Tokummia katalepsis helps to understand the origin of mandibulates

Tokummia katalepsis fossil (Photo courtesy Aria / Jean-Bernard Caron)
Tokummia katalepsis fossil (Photo courtesy Aria / Jean-Bernard Caron)

An article published in the journal “Nature” describes the discovery of fossils of a species of marine arthropods that lived a little more than 500 million years ago in the Permian period. Calling Tokummia Katalepsis, this species is one of the many discovered in Burgess Shale and is important because according to Cédric Ariz and Jean-Bernard Caron of the Royal Ontario Museum (ROM) it shows the origin of mandibulates (Mandibulata), a group of arthropods that includes millipedes, crustaceans and insects.

Today, mandibulates are spread all over the world, on the mainland, in the seas and in the air, with a remarkable diversity of millions of species that represent a huge evolutionary success for this arthropod group. The development of jaws was such an evolutionary advantage that this group survived various mass extinctions, thriving with and spreading in very different ecosystems. However, there were still a number of mysteries about their origin and the characteristics that determined their success.

In 2014, a paleontological research led by the ROM in Burgess Shale collected several specimens in an excellent state of conservation of the species called Tokummia katalepsis. They were discovered in sedimentary rocks dated just over half a billion years near Marble Canyon in Kootenay National Park, British Columbia. It’s one of the many strange animals that evolved during the so-called Cambrian explosion but it could be a key to understanding how mandibulates emerged.

Tokummia katalepsis was small, with a length reaching about 10 centimeters (4″), yet it was one of the greatest predators of its time. This animal had large toothed jaws, but also large front claws just like modern mandibulates. These are structures that were already complex, with large and powerful pincers to hunt prey but at the same time delicate, with a shape that reminds a can-opener.

Perhaps those pincers weren’t strong enough to use them on shelled-prey but on soft animals, though of considerable size. One possibility is that Tokummia katalepsis ambushed its prey hiding in the mud at the bottom of the sea where it lived. After using its pincers to hit its prey, it used its jaws to cut their meat into easily digestible pieces, a revolution among arthropods.

Tokummia katalepsis’ body has a series of characteristics that in some respects seem to be a mix of those of today’s mandibulates. For example, it’s composed of many segments, over 50, such as millipedes, but is covered by a large carapace and its segments have tiny projections that can now be found in the larvae of some crustaceans.

The researchers also found some affinity between Tokummia katalepsis and some other fossilized arthropod species discovered in Burgess Shale as Branchiocaris, Canadaspis, and Odaraia. They could form a group of animals that are at the origin of today’s mandibulates.

Tokummia katalepsis reconstruction (Image courtesy Lars Fields)
Tokummia katalepsis reconstruction (Image courtesy Lars Fields)

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