(Intro)

In Which Emily Goes Looking for Fossil Sharks

Text: Hammerheads! But where are the fossil sharks?

Emily: The fossil sharks are hiding today!

Meanwhile... 

But look! A fossil-shark clue!

*(fig. 1) The Megalodon Tooth* (00.35)

This is the tooth of the Carcharocles megalodon, or better known as the megalodon shark. These unfathomably large predatory giants swam in our oceans from about fifty-two million to about two million years ago.

Based off of the large size of this tooth, it's estimated that megalodon was up to fifty feet or fifteen meters in length. Compare that with the relatively wimpy Great White Shark of today at about only thirteen feet, or four meters, in length. And scientists think that it hunted wales - with a bite that was far stronger than that of T-rex.

But, like modern-day sharks, Megalodon had a cartilaginous skeleton, meaning one made out of cartilage rather than mineralized osseous tissue, also known as bone. And, because cartilage does not mineralize to the extent that bone does, a requisite of the fossilization process, it's very rarely found in the fossil record.

So, when searching for fossil sharks, all that typically remains are their bone-like teeth, which are actually just hardened, plate-like scales. This leaves scientists to puzzle out what the rest of the creature would have looked like, or actually how big it was, with teeth as the only clue.

*(fig. 2) The Curious Case of the Helicoprion Fossil* (01:47)

All that remains of the Helicoprion from two hundred and seventy million years ago are its saw-like, whirled-up teeth, and, because nothing quite like these teeth exist either today or elsewhere in the fossil record, it has been a palaeontological mystery for scientists.

What sort of animal had these teeth? Where exactly did they fit on the animal? And what's their function?

When this fossil whirl was first discovered, paleontologists thought it might be some kind of shelled cephalopod, kind of like a nautilus (02:17). But, Russian geologist Alexander Petrovich Karpinsky named the Helicoprion in 1889 after identifying that its petrifications, the process in which organic material is converted into stone, more closely resembled that of a shark-like fish. And, his best guess to its fit and function, he thought that Helicoprion teeth whirled out from its knows - kind of like a saw-toothed party-horn.

Paleontologists, over the years, and revised just where they think the Helicoprion's toothy whirl was located on the body. Some conjectured that it could have been anywhere from the tail, to the fin, to an elongated lower jaw. But, in an effort to better understand these creatures, scientists are using new technology in order to look into fossils like ours.

Researchers at the Idaho Museum of Natural History were able to CT scan a Helicoprion fossil and found traces of teeth as well as cartilage from the jaw and skull.

Their findings? The toothy whirl completely filled the lower jaw and and didn't uncoil quite like a party horn. Perhaps more surprisingly, the CT scan revealed that the Helicoprion didn't have any upper teeth at all. As for function, just how did they use this toothy whirl to eat without any teeth on their upper jaw? Well, that's the next question in this prehistoric mystery.

The bigger mystery? If Helicoprion is the only example of this bizarre feature, how did this toothy whirl evolve to begin with?

*(Credits)*