Some 375 million years in the past, armored fishes dominated a watery world. Referred to as placoderms, these primitive jawed vertebrates got here in all styles and sizes, from small bottom-dwellers to large filter-feeders. Some, just like the wrecking-ball-shaped Dunkleosteus, had been among the many ocean’s earliest apex predators.
Few of those historical oddities had been weirder than the aptly named Alienacanthus. Found in Poland in 1957, this Devonian Interval fish was initially recognized for a set of huge, bony spines. However the current discovery of a fossilized Alienacanthus cranium, described in a paper revealed Wednesday within the journal Royal Society Open Science, reveals that these spines had been really the fish’s elongated decrease jaw. Measuring twice so long as the remainder of the fish’s cranium, this decrease jaw gave Alienacanthus nature’s most excessive underbite, and, maybe, a stiff decrease lip.
“It’s nonetheless very alien trying so the identify may be very becoming,” stated Melina Jobbins, a paleontologist who research placoderms on the College of Zurich and is an creator on the paper.
Since its discovery within the Nineteen Fifties, Alienacanthus is thought solely from just a few fossils found within the mountains of central Poland and Morocco. Through the Late Devonian Interval, these areas had been submerged coastlines on reverse ends of an enormous sea separating northern and southern supercontinents. However many of those fossils are fragmentary and provide little element on what this unusual fish seemed like.
Over the previous twenty years, researchers have uncovered further well-preserved Alienacanthus fossils in European museum collections. Dr. Jobbins teamed up with researchers from a number of of those museums to pool collectively the fossil bits and extra precisely describe the traditional fish.
The important thing to cracking this fishy enigma was an almost full Alienacanthus cranium measuring greater than two and a half ft that originated in Morocco and is at present within the assortment of the College of Zurich’s Palaeontological Institute. With the weather of the cranium nonetheless articulated, the staff realized that Alienacanthus’s oddly formed spines had been really its decrease jaw bones. This made the fish even stranger: When it closed its mouth, the placoderm resembled an upside-down billfish with a protracted, beaklike backside jaw.
Whereas fishes like swordfish and sawsharks wield dramatic upper-jaw protrusions, only a few species possess elongated decrease jaw protrusions. At the moment, this function is seen solely in a bunch of small fish known as halfbeaks. However the relative size of Alienacanthus’s decrease jaw was 20 p.c larger than a halfbeak’s. Alienacanthus’s jaw was additionally proportionally longer than comparable buildings seen in prehistoric sharks and porpoises, making the fossil fish the undisputed champion of the underbite.
The prolonged jaw might have helped Alienacanthus sift via sediment, which is how trendy halfbeaks make the most of their shovel-like jaws. One other speculation is that the prehistoric fish wielded its decrease jaw to stun or injure prey.
Dr. Jobbins thinks the elongated jaw, which was studded with recurved tooth that prolonged properly previous the place its high jaw ended, most definitely served as a entice. “Principally it might invite prey in after which they’ll’t get out as a result of there’s just one approach to go,” she stated. Alienacanthus’s shorter higher jaw might transfer independently of the decrease jaw and snap shut as soon as a fish or squid was in too deep.
This snaggletoothed fish is an intriguing evolutionary oddball. As a placoderm, Alienacanthus belonged to the earliest teams of vertebrates to develop advanced jaws. The fish gives a glimpse of simply how excessive jaws may very well be proper after the now-widespread function originated.
Alienacanthus additionally represents one of many ultimate chapters of placoderm evolutionary ingenuity. Inside 15 million years of the looks of Alienacanthus’s toothy mug, these armored fish had been worn out and changed by sharks.
