Paleontology collections are wonderful. Shelves and cabinets hold anywhere from thousands to hundreds of millions of years of life’s history, assembling giant ground sloths, Cambrian oddballs, petrified plants, and other fantastic organisms into a fossilized menagerie. And as much as I’ve enjoyed my opportunities to explore prehistoric storage on my own, it’s even better when curators can spare a few minutes to show off their favorite treasures.
The last time I had the pleasure of getting such a tour was in late February. I had made an appointment with paleontologist Ted Daeschler to chat about our early tetrapod ancestors, and he was kind enough to give me a whirlwind tour of the collections held at the Academy of Natural Sciences. Zipping from one drawer to the next, Daeschler deftly navigated the tight space between the cabinets to show off a variety of beautifully-preserved fossil fish from a variety of times and places.
Many of the fish were preserved whole, as if they had been frozen in mid-swim, but one drawer was lined with the remains of an animal only known from pieces. Light glinting off the enamel-like coating of their teeth, the fossils were curved tooth whorls given the name Edestus heinrichi. In life, the whorls of this ratfish relative were arranged in a vertical pair – what must have looked like evolution’s attempt at pinking shears. There’s nothing on Earth today with jaws like that.
Given that our species is over 306 million years too late to observe Edestus in action, there’s been plenty of debate about how this ancient fish employed its wicked grin. The most obvious answer – that Edestus snipped prey with scissor jaws – doesn’t work. (This has been a recurring problem in paleontology – just because a structure looks like a human-invented tool, it doesn’t mean the structure was used the same way.) The tooth whorls of Edestus curved away from each other along their length, so much so in the early species Edestus newtoni that the fish must have looked perpetually puckered to give a serrated kiss. Only a few teeth at the very back of the row would actually slide past each other to shear through shell or scale.
With the scissor hypothesis in doubt, paleontologists espoused a variety of speculative functions. University of Colorado paleontologist Wayne Itano ran down the list in a 2014 paper on Edestus. Perhaps Edestus trawled for jellyfish, burrowed in the mud after clams, or scraped shellfish off their moorings. Or maybe Edestus snagged prey with its upper jaw and sawed through it with the lower, working its fishy chin back and forth to cut victims into manageable chunks.
All these ideas are easily-imagined, but they’re also without supporting evidence. A better contender, proposed by John Long and elaborated on by Itano, is that Edestus subdued prey with a bit of prehistoric headbanging.
While there’s nothing quite like Edestus alive today, there are fish that capture and kill prey with some pretty strange anatomy. Both sawfish and billfish whip their snouts back and forth to stun and slice their prey. Edestus, Long and Itano have suggested, might have done the vertical version of this, throwing their jaws up and down to injure and lacerate fish and cephalopods.
Some Edestus teeth might bear the marks of such throes. On one specimen of Edestus newtoni, Itano observed, the teeth at the furthest reaches of the whorl have intact tips and worn-down serrations. Edestus was slicing into prey rather than puncturing it. This mode of attack was best-suited to prey on the softer side, but Edestus may have occasionally tried tougher fare. One Edestus tooth, Itano notes, has an abraded tip and indicates that its owner probably busted a crown on something hard and had to live with the broken point until the tooth was pushed out.
And while circumstantial, there’s another line of evidence that Edestus were master shredders. The black shales of Indiana, Itano points out, are famous for “amputated fish”. Some are only heads. Others tails. And a few have deep lacerations that left only a fragile band of tissue connecting the severed morsels. Edestus fossils have been found in the same deposits, and, lacking any evidence of a Carboniferous Freddy Krueger, the fierce fish is a top suspect.
Itano, W. 2015. An abraded tooth of Edestus (Chondrichthyes, Eugeneodontiformes): Evidence for a unique mode of predation. Transactions of the Kansas Academy of Science. 118 (1-2): 1-9
Itano, W. 2014. Edestus, the strangest shark? First report from New Mexico, North American Paleobiogeography, and a new hypothesis on its method of predation. The Mountain Geologist. 51 (3): 201-221