From National Geographic :
A fearsome fossil claw discovered in Germany belonged to the biggest bug ever known, scientists announced Tuesday.In those days, the oxygen content was much higher, removing present-day limits. Their prey was also larger, heavily armoured fish. From the Los Angeles Times :
The size of a large crocodile, the 390-million-year-old sea scorpion was the top predator of its day, slicing up fish and cannibalizing its own kind in coastal swamp waters, fossil experts say.
Jaekelopterus rhenaniae measured some 8.2 feet (2.5 meters) long, scientists estimate, based on the length of its 18-inch (46-centimeter), spiked claw.
The find shows that arthropods—animals such as insects, spiders, and crabs, which have hard external skeletons, jointed limbs, and segmented bodies—once grew much larger than previously thought, said paleobiologist Simon Braddy of the University of Bristol in the United Kingdom.
One of its claws might feed an entire family, but this sea creature would be more likely to eat the family.Quite.
And what does an 8-foot sea scorpion eat? Pretty much anything it wants to, Braddy said. The creature would have been the dominant predator in its environment, feasting on armored fish, early vertebrates, other varieties of arthropods and even on smaller sea scorpions.