Megalodon is the T. rex of the prehistoric shark world—it might have looked like a Great White, only way, way bigger, and it’s everybody’s favorite. It’s had its moment in the sun, even starring in a fake Shark Week documentary saying that it’d been found in modern waters (don’t worry—megalodon has been extinct for millions of years). But The Field Museum is home to some really bizarre sharks that lived millions of years before dinosaurs were even a twinkle in the universe’s eye. None of these have starred in a Shark Week documentary (yet), but it’s only a matter of time before these beautiful weirdos become household names.
These sharks, which lived around 360-260 million years ago, had tooth-like “brushes” on their heads and on top of their dorsal fins. We don’t know why they had these features, though—as with many unusual physical characteristics in the animal kingdom, scientists’ best guess is that they were there to be either scary or sexy. Their heads and dorsal fins aren’t the only spiny part of Stethacanthus, either—they’re some of the first sharks to possess dermal denticles, the tiny, sharp skin protrusions that you still see in shark skin today.
Edestid—X-rays reveal pinking shear jaws
Lots of early shark fossils are preserved in slabs of black shale, a dark, oily rock that can be hard to see fossils in. To better see the fossils, scientists take X-ray images of the shale slabs—the fossils are a different density than the rock around them, so they stand out in the X-rays, just like your bones do when you get an X-ray of your arm. These X-rays reveal features that are hard to see with the naked eye, like the pinking shear-like jaws of the Edestid sharks. Their serrated teeth grew in long, curved brackets. The biggest members of this family were up to twenty feet long—the size of a Great White. And their cousin, Helicoprion, took those overlapping rows of teeth to a terrifying new level.
With the exception of their teeth, sharks don’t really have bones—their skeletons are made out of cartilage, which tends not to fossilize very well. That means that paleontologists have to fill in the blanks with their best guesses, like with Helicoprion. These sharks are known for their “tooth-whorls”— spiraling jaws lined with a long row of sharp, overlapping teeth. These tooth-whorls are often the only part of the sharks that gets fossilized, so scientists have to make their best guess at what the animal looked like in its entirety. For a long time, scientists thought Helicoprion might have been able to swing around its spiral jaw like a flailing tornado of teeth, snagging smaller fish fool enough to swim near it. A newer study indicates that its jaw was actually enclosed, rather than free-swinging, and that when the jaw closed, the teeth rotated almost like a buzzsaw. And it might not actually have been a shark—CT scans of fossils seem to show skull bones that you wouldn’t see in a fish with a cartilage skeleton. Helicoprion was probably more closely related to ratfish, which are pretty freaky in their own right.
Bandringa—baby sharks in Illinois
For a long time, scientists assumed that this shark, called a Bandringa, was a tiny adult, but as it turns out, this sweet little four-inch sharklet would have grown up to be ten feet long. This little shark with a giant schnozz is just a baby, from the world’s oldest shark nursery right here in Illinois. Three hundred and seven million years ago, the area near modern-day Chicago was the swampy coastline of a shallow, tropical sea, and it was a popular destination for river-dwelling sharks to lay their eggs. We don’t think Bandringa was a fierce predator—it probably used that long nose to root around for invertebrates in the riverbed—but we’d still want to play it safe around ten-foot-sharks.