Royal Ontario Museum paleontologists announce the discovery of an incredible fossil repository that preserves the brain and nervous system of an ancient three-eyed sea predator. The animal belonged to an ancient extinct offshoot of the arthropod evolutionary tree called Radiodonta, distantly related to modern insects and spiders. Details of the study are published in Current Biology.

An extraordinary discovery

Researchers made the discovery in the Burgess Shale. It is a formation in the Canadian Rocky Mountains of British Columbia known for its fossilized animal remains more than 500 million years old. All represent a new species called Stanleycaris hirpex.

Although Cambrian fossilized brains are not new, this find is notable for its amazing preservation quality and large number of specimenssaid Joseph Moysiuk, lead author of this work. ” We can even make out fine details like visual processing centers that feed the large eyes and traces of nerves entering the limbs. Details are so clear it feels like you were looking at a dead animal yesterday“.

Even more interesting: the remains of the brain and nerves were preserved in 84 of these fossils. All would have evolved approximately 506 million years old.

Before that, there had been few other finds of fossilized brains, particularly from the Cambrian period. However, it’s still something pretty rare‘ adds the researcher. ” Furthermore, most species with fossilized brains are represented by only one or two specimens.

Stanleycaris hirpex
Two fossil specimens of Stanleycaris hirpex. Credit: Royal Ontario Museum/Jean-Bernard Caron
Stanleycaris hirpex
Artistic reconstruction of the species. The superior individual is transparent to show internal organs. The nervous system is shown in light beige. The digestive system is shown in dark red. Credit: Sabrina Capell.

A three-eyed predator

Although it was small (less than twenty centimeters long), S.hirpex was probably a formidable predator. The creature was clad in long, rake-like spikes to scour the seabed and side flaps to help it glide through the water two huge appendages at the level of the mouth, which was probably used to crush its prey.

Fossils show that the brain of S.hirpex was divided into two segments : the protocerebrum and the deuterocerebrum. The first was connected to its eyes while the second was connected to the forehead claws. This brain structure differs from the three-lobed structure of modern arthropods, which are distant relatives S.hirpex, like insects. ” The preservation of the brains of these animals gives us a direct glimpse into the evolution of the nervous system from the perspective of the fossil record.‘ the authors point out.

Another interesting aspect of S.hirpex was his oversized third eye, located between his two side eyes. This is the first time such a trait has been observed in this species. Paleontologists still do not know its function. They still assume that this could have third eye helped the animal to orient itself or track its prey.

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