These fossils originated from the Burgess Shale in western Canada, one of the world's richest source of fossils from the period. The findings identified a key point in the evolutionary transition from soft to hard bodies in early ancestors of arthropods, group that contains modern insects, crustaceans and spiders.

"The anterior sclerite has been lost in modern arthropods, as it most likely fused with other parts of the head during the evolutionary history of the group," said Javier Ortega-Hernandez, researcher from Cambridge University's department of earth sciences, who authored the study.

A hard plate, called the anterior sclerite, and eye-like features at the front of their bodies were connected through nerve traces originating from the front part of the brain. The results allowed new comparisons with anomalocaridids, a group of large swimming predators of the period.

The preserved brains in these fossils have enabled to recognise the anterior sclerite as a bridge between the head of anomalocaridids and that of more familiar jointed arthropods. These ancient brains processed information like in today's arthropods, and were crucial for interacting with the environment, detecting food, and escaping from predators.

"But what we're seeing here is an answer to the question of how arthropods changed their bodies from soft to hard. It gives us an improved understanding of the origins and complex evolutionary history of this highly successful group," Ortega-HernAindez concluded.

The results appeared in the journal Current Biology.


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