Daddy longlegs, officially named Harvestmen, had an extra pair of eyes 305 million years ago. The discovery comes after finding a fossil in France, something incredibly rare for these tiny creatures.
Daddy longlegs are on every continent except Antarctica. They come in a variety of sizes, but all species of longlegs have only one pair of eyes. This sets the longlegs apart from other spiders, which commonly have eight pairs of eyes. In fact, longlegs have closer relatives than spiders – scorpions, mites and ticks are closer family.
But 305 million years ago the daddy longlegs were trying harder to blend in with their spider cousins. A fossil sample was taken to scientists at the American Museum of Natural History in New York City and the University of Manchester in England. They scanned the fossil using sophisticated x-ray techniques, and the high resolution scan revealed an extra pair of eyes. Modern day longlegs have either median eyes or lateral eyes – eyes located either near the middle of the body or on the side. The ancient longlegs ancestor had both. On closer look, it turns out that all daddy longlegs have a pair of unused “eye stalks” where the 305 million-year-old longlegs had used both.
It’s amazing that the ancient longlegs’ fossil survived. Longlegs are so tiny that any fossilized remains are easily crushed. This particular longlegs fossil was “compacted into rock, an iron carbonate mineral called siderite grew around it to form a nodule, otherwise known as a concretion,” according to study leader Russell Garwood, a paleontologist at the University of Manchester. He explained that, “Arachnid eyes in general are pretty variable, and different groups tend to lose or modify their eyes quite a bit”.
Why daddy longlegs evolution chose to forgo the extra pair is unknown. Unlike most spiders, longlegs scavenge for decaying plants and animals on the forest floor. This could explain why spiders kept their many eyes and longlegs did not. Hunters need sharp senses and expert sight – the same characteristics that inspired Spider Man. Scavengers can manage with less and daddy longlegs make do with their one set to navigate the leafy underworld. Most of their senses are used to detect threats and their next meal.
The big score for Garwood’s team has been finding something previously never questioned, revealing the marvels of evolution. He said, “This work shows that by combining evolutionary-developmental biology, fossils, and evolutionary biology, we can explain otherwise enigmatic features in living groups.”