Scurrying along the beds of oceans, lakes, and rivers, the ancient arthropods known as sea scorpions were menacing-looking predators. Surviving until the later Permian, they were top predators that feasted on early vertebrates.
Now, in a paper published in the journal American Naturalist, researchers suggest that these critters were even more daunting than previously imagined, using their spiked tails to slash at their victims and eviscerate them before tearing them apart with their claws.
At the time they were swimming the oceans and waterways some 400 million years ago, eurypterids were a hugely diverse group of creatures. While most reached only around 20 centimeters (8 inches) in size, the group contains some of the largest known arthropods ever to have lived, with one formidable species reaching a pretty horrifying 2.5 meters (8 feet) in length.
With many species possessing a pair of front claws, segmented bodies, and a long flexible tail ending in spines, the eurypterids are frequently referred to as “sea scorpions”. The sea scorpions were among the most voracious and abundant aquatic predators during much of the early evolution of vertebrates, and were most probably preying on early fishes.
The eurypterids were dominant predators at the time. Wikimedia Commons/CC BY 2.0
The role of their long tails has long perplexed many paleontologists. Some have suggested that the spines on their tails could have delivered venom – much like their terrestrial namesake – though this is disputed as to date no evidence has been produced to back this up. In fact, it has been suggested that unlike other marine critters like lobsters, the sea scorpions were unable to flex their tails up and down. While lobsters use this motion to help propel them, eurypterids had a specialized paddle-like pair of appendages thought to do this instead.
Researchers from the University of Alberta instead suggested another way in which the arthropods may have used their tails. Rather than moving them up and down, the sea scorpions could have moved them from side to side in a slashing motion. Coupled with the serrated spines on some species’ tails, they hypothesize that the sea scorpions may have held their prey with their claws, before cutting at them from the side with their tail.
“This means that these sea scorpions could slash their tails from side to side, meeting little hydraulic resistance and without propelling themselves away from an intended target,” explains lead author Scott Persons in a statement. “Perhaps clutching their prey with their sharp front limbs eurypterids could kill using a horizontal slashing motion.”
So it would seem that for early vertebrates, there may have been even more of a reason to avoid the menacing sea scorpions.