Tuesday, April 1, 2014

The fossilised footprints made by a SPIDER: Tarantula-sized arachnid left marks as it walked 260 million years ago

It’s taken almost half a century to discover what creature made these tiny fossilised footprints, but researchers are now sure they were made by an ancient spider.

The prints were uncovered during the 1960s in Northern Arizona by palaeontologist Raymond Alf.

Following years of experiments and studies, experts now claim the prints were made by a 2.5-inch long tarantula-sized arachnid, and date back approximately 260 million years.

The fossils are on display in the Hall of Footprints at the Raymond M Alf Museum of Palaeontology, named after the palaeontologist who made the discovery.

Alf discovered the imprints in rock during an expedition to the deserts of Arizona in 1968, which include the Painted Desert and parts of the Mojave Desert.

According to the museum, the moisture in the sand preserved the prints and as the sand dried in the sun, these prints became permanent.

This sand eventually hardened into rock.

After retrieving the fossils, Alf carried out a number of experiments which involved walking spiders and scorpions over inkpads and paper to mimic the shape and size of the prints.

These tests were repeated by geologist Christa Sadler in 1993 and both experiments concluded the prints were made by a tarantula-sized spider.

Expert Anthony Martin told Wired the prints reveal the legs on each side of the creature would have have been moving at different times, which is ‘very typical pattern with terrestrial arthropods.’

Alf museum curator Andrew Farke added the arachnid was likely to have been 2.5-inches in length, and research suggests the fossils are 260 million-years-old.

In January, researchers from Kansas discovered a rare spider fossil in China, after uncovering a similar fossil in the same region three years earlier.

The original female fossil, found in the Daohugou beds of Inner Mongolia in 2011, was so well preserved experts claimed it was part of the Nephila species.

But the more recent discovery of a similar-sized male fossil cast serious doubt over this theory because its relative size didn’t fit the Nephila mould.

In fact, the researchers were so baffled by the differences, they proposed a new genus called Mongolarachne, to describe the creature.

Spider fossils are rare because their bodies are soft, but this pair was found in volcanic deposits and experts believe these deposits may have buried the pair at the bottom of a lake, perfectly preserving them.

The fossils are roughly the size of the spider's modern-day descendants, with a body one-inch long and more than half an inch wide, and legs that stretch to 2.5 inches.

It is thought the arachnids roamed the east 165 million years ago – almost a millennia after the spider who left the footprints in Arizona.

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