Scientists Rethink Evolution of Insects After Discovery of 500 Mn Years Old Fossils

A new study of a fossil cache sheds fresh light on the evolutionary history of insects and spiders, notably the brain, eyesight, and head shape. The fossils comprised well-preserved remnants of the brains and neurological systems of Stanleycaris, a three-eyed predator.

Despite the predator being over half a billion years old, the neural structures have been preserved.

There have been 84 fossils discovered with complete brains and nerves from Burgess Shale. The creature is a member of the Radiodonta branch of the arthropod evolutionary tree. The creature is related to modern-day insects and spiders.

Joseph Moysiuk, lead author of the research says, “While fossilized brains from the Cambrian Period aren’t new, this discovery stands out for the astonishing quality of preservation and a large number of specimens. We can even make out fine details such as visual processing centers serving the large eyes and traces of nerves entering the appendages. The details are so clear it’s as if we were looking at an animal that died yesterday.”

“We conclude that a two-segmented head and brain has deep roots in the arthropod lineage and that its evolution likely preceded the three-segmented brain that characterizes all living members of this diverse animal phylum,” he adds.

The brain of modern arthropods is made up of three parts: the protocerebrum, the deutocerebrum, and the tritocerebrum.

While a segment difference may not appear to be significant, it has far-reaching scientific ramifications.

Because many arthropod organs have repeating copies in their segmented bodies, studying how segments line up between various species is critical to understanding how these structures developed within the group.

In addition to its stalked eyes, Stanley Caris hiprex has a big central eye at the front of its head, which had never been seen in a radiodont previously.

“The presence of a huge third eye in Stanleycaris hirpex was unexpected,” told Dr Jean-Bernard Caron, the Richard Ivey curator of invertebrate palaeontology at the Royal Ontario Museum.

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