The fossilized brain of a three-eyed shrimp-like creature that swam the oceans 500 million years ago could lead to rethinking the evolution of insects and spiders.
The creature, named Stanleycaris hirpex, is described as “the essence of nightmares”. It had two eyes on two legs, a third eye in the middle of its head, a surprisingly round mouth with teeth, and front claws with an impressive array of spikes.
Stanleycaris lived during the Cambrian Explosion, a period of rapid evolution when most of the major animal groups appeared in the fossil record.
It belonged to an ancient, extinct branch of the arthropod evolutionary tree called Radiodonta, closely related to modern insects and spiders.
Despite the strange appearance of Stanleikaris, the contents of its head have intrigued scientists.
In studying more than 250 506-million-year-old Stanleycaris fossils, they found that the brain and central nervous system were still preserved in 84 fossils.
They showed that the brain of Stanleycaris consisted of two parts, rather than three, as in modern insects, which shed new light on the evolution of the brain, vision and structure of the head of arthropods.
Fossils of Stanleycaris were collected from the Burgess Shale – fossil-bearing deposits exposed in the Canadian Rockies in British Columbia – in the 1980s and 1990s.
It is rare to find fossilized soft tissues. Most fossils are bones or hard body parts such as teeth or exoskeletons, while brains and nerves are composed of fat-like materials that do not normally exist.
They showed that the brain of Stanleycaris consists of two parts – the primary brain and the cerebellar microbrain, connected to the eyes and front claws, respectively. These parts of the brain control vision and antenna signals in modern arthropods.
In modern arthropods, such as grasshoppers and other insects, the brain consists of three parts – protocerebrum, deutocerebrum and tritocerebrum.
Although the difference in one part may not seem like a decisive factor, according to the researchers, it actually has serious scientific consequences.
Because repeating copies of many arthropod organs can be found in their segmented bodies, knowing how the parts line up between different species is key to understanding how these structures evolved.
Stanleycaris was a representative of radiodonts, the largest predators of the Cambrian period.
This includes the famous Anomalocaris, which is at least 3 feet 3 inches (1 m) long.
In addition to a pair of haunting eyes, Stanleycaris has a large central eye on the front of its head, a feature not previously seen in the sensory realm.
The study was published in the journal Current Biology.
Source: Daily Mail