Fossils Half a Billion Year Old Reveal Three-Eyed Creature

Paleontologists from the Royal Ontario Museum announce the discovery of an incredible cache of fossils preserving the brain and nervous system of an ancient three-eyed marine 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 exceptional discovery

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

Although fossilized brains from the Cambrian period are not new, this discovery stands out for the astonishing quality of preservation and the large number of specimens“, said Joseph Moysiuk, main author of this work. ” We can even make out fine details such as visual processing centers serving the large eyes and traces of nerves entering the appendages. Details are so clear it feels like looking at a dead animal yesterday“.

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

Prior to this, there had been only a few other finds of fossilized brains, particularly from the Cambrian period. However, it is still something quite rare“, adds the researcher. ” Additionally, most species with fossilized brains are represented by only one or two specimens.

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

A three-eyed predator

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

Fossils show that the brain of S. hirpex was divided into two segments : the protocerebrum and the deutocerebrum. The first was connected to its eyes, while the second was connected to the frontal claws. This brain structure differs from the three-lobed structure of modern arthropods which are distant relatives of S. hirpex, such as insects. ” Preserving the brains of these animals gives us direct insight into the evolution of the nervous system from the perspective of the fossil record.“, underline the authors.

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

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