Earliest Tool Use Was to Build a 'Space Suit'
"The first tool-users in the world may have been scorpion-like sea beasts. The extinct animals used other creatures' shells to help them breathe on land 500 million years ago, new research suggests.... Sea scorpions—thought to be among the first marine animals to evolve for life on land—breathed underwater using gills on their tails. The odd drag marks could have been from the coiled shells of snails or similar critters, which the ocean-dwelling scorpions stuffed their tails into so they could venture above water, the researchers suggest.
Humid air trapped inside the shells might have protected the sea scorpions' gills from drying out during brief forays into the open air —like reverse scuba gear."