From National Geographic News:
Five foot long tracks of a six-legged water scorpion reveal that Hibbertopterus could have lumbered along the riverbanks of Scotland 330 million years ago,
Illo © Nature 2005
"There's been lot of debate about this particular [species of] water scorpion—whether it could only live in water or if it could come out. What the track shows is they could come out at least for short intervals," Martin Whyte, a geologist at the University of Sheffield in England said.
The track itself is 20 feet (6 meters) long and about 3 feet (1 meter) wide. The creature walked in-phase, with each pair of limbs moving forward at the same time rather than alternating, like a human gait. Also, the scorpion's stride averaged 10.6 inches (27 centimeters) long, short enough that they overlapped. The track also features a central groove left by the water scorpion's dragging tail, leaving indications of jerky movements.
"The whole thing adds up to fairly look as though the body [was] heavy and the animal was moving quite slowly," Whyte said. "For that reason I think it was out of the water. Had it been in [the water], water would've buoyed up the tail."
By about 360 million years ago the transition of lobe-finned fish—prehistoric fish with fleshy fins—to four-limbed tetrapods was nearly complete. The newly discovered trackway, which is dated to 330 million years ago, therefore suggests that some of the earliest tetrapods would have confronted these giant water scorpions as they scurried about the shore.
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