Have spiders gotten dumber over time? That's one possible conclusion from 50 well-preserved fossils excavated from 520-million-year-old rocks in southwestern China.
The fossils belong to a 6cm-long early arthropod - a group that includes insects; spiders; scorpions; and crustaceans such as shrimp, crabs, and lobsters - which had a surprisingly modern brain.
Several specimens of the species, Fuxianhuia protensa (left), contain dark areas within their eye stalks (see fossil, above right; gray areas in sketch, bottom right) that represent preserved clusters of neural tissue, including clumps along the optic nerve (labelled one through three in the sketch) and the brain (lowermost mass).
The eye stalks were preserved in many different positions - a sign that they were flexible and that the creatures could control their movement, the researchers report online today in Nature.
Furthermore, they say, the appearance of such a complex brain early in arthropod evolution suggests that the nervous systems of modern-day arthropods with simpler brains - such as spiders, scorpions, and the crustaceans known as water fleas - were at some point downsized by evolution, a contrast with previous notions that the brains of arthropods in those lineages had remained simple since arthropods first arose.
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