A newly discovered, well-preserved fossil eurypterid adds a weapon to the known arsenal of these ancient formidable predators: a slapping, slashing tail spine. Its wielder, Slimonia acuminata, represents a new species of eurypterid that once even feasted on our early fish ancestors. It is described in the journal The American Naturalist.
“Slimonia would have lurked in the shallow waters of lagoons and lakes along the coast of primordial Europe, during the Silurian Period (443.7–416 million years ago),” lead author Scott Persons, of the University of Alberta’s Department of Biological Sciences, told Seeker. “At the time, our vertebrate ancestors were primitive fish.”
Persons and co-author John Acorn studied Slimonia’s remains, which were unearthed at the Patrick Burn Formation near Lesmahagow, Scotland. This sea scorpion was not one of the largest eurypterids, given that it measured about a foot and a half long. Its weaponized tail gave it an edge over most other predators, though.
As for how this predator dispatched prey, Persons said that Slimonia probably used its chelicerae, or segmented mouth parts, to hold onto our ancestors and other victims, “while repeatedly striking with sidelong blows from the tail spine.”
Unlike today’s lobsters and shrimps, which can flip their broad tails up and down to help them swim, sea scorpion tails were vertically inflexible but horizontally highly mobile. A cool feature was that they could aggressively slap and slash sideways, while still meeting a minimum of hydraulic resistance. This helped to prevent them from propelling themselves away from an intended target with each forceful strike.
The other top ocean predators at the time were enormous cephalopods, meaning the relatives of modern squid, octopus and the chambered nautilus.
“These were real Lovecraftian monsters, with sharp beaks and lots of tentacles,” Persons explained, referring to the horror fiction of H. P. Lovecraft.
The giant squid surely feasted on our ancient ancestors, but also probably took on Slimonia from time to time.
He added that, unlike sea scorpions, whose fossilized shells reveal their full body size and shape, the remains of ancient cephalopods require more scientific guesswork. That's because their soft bodies do not easily fossilize.
Clues to their existence are cephalopod shells, some of which were spiral shaped, like a snail’s, while others were swirl shaped, Persons said, “like a tall helping of soft-serve ice cream.”
“Of the swirl-shelled Silurian cephalopods — say that five times fast — a few grew to well over a meter (3.3 feet) in length,” he continued. “Like modern squid, they could have reached out with their tentacles, snagged a victim and then pulled it back into their mouths.”
Read more at Discovery News