Five foot seven and claws out of its head: meet Earth's first big predator

Fossils of Pentecopterus decorahensis, which hunted in the oceans half a billion years ago, discovered in Iowa river bed

Earth's first big predatory monster was a giant underwater scorpion that reigned in the ocean almost half a billion years ago, well before the dinosaurs, scientists have discovered.

The creature grew to 170 centimtres (5ft 7in) and had a dozen claw arms sprouting from its head, as well as a spiked tail. Geologists at the Iowa Geological Survey found 150 pieces of fossils about 18 metres under the Upper Iowa river, part of which had to be temporarily dammed to allow them to collect the specimens.