Paleontologists Unravel Secrets of ‘Enigmatic’ 33-Foot Prehistoric Shark After Fossil Discovery

Scientists didn’t know much about Ptychodus, an ancient shark genus, because its remains were usually just fragments. Now, complete fossils reveal its body shape and hunting habits

An artist's illustration of two giant Ptychodus sharks eating sea turtles and ammonites in open water
An artist's illustration of two Ptychodus sharks eating sea turtles and ammonites in open water. F. Spindler

After years of uncertainty, a prehistoric shark mystery has at last been solved—thanks to the recent discovery of remarkably complete fossil skeletons in northeastern Mexico.

The remains belong to a little-known prehistoric shark genus called Ptychodus, which has been a “long-standing enigma” for scientists, according to the new paper, published Wednesday in the journal Proceedings of the Royal Society B.

While researchers have found fossilized fragments of Ptychodus across much of the world, these remains have been largely incomplete—just bits of cartilage, vertebrae and teeth. This left paleontologists with no way to discern what the shark’s fully body looked like, or how it behaved. Now, scientists have the pieces they were missing.

“The discovery of complete Ptychodus specimens is really exciting, because it solves one of the most striking enigmas in vertebrate paleontology,” Romain Vullo, a paleontologist at the University of Rennes in France and the study’s lead author, tells Live Science’s Melissa Hobson.

“Its general appearance has remained a mystery up to now,” Vullo adds to the Guardian’s Nicola Davis.

The newly unearthed specimens, discovered in limestone quarries in Nuevo León, Mexico, have offered never-before-seen details of the ancient predator. Now, paleontologists report Ptychodus could grow to be a staggering 33 feet long, was likely a close relative of today’s great white sharks and crunched on hard-shelled creatures with unique grinding teeth.

Ptychodus has long been a classic example of teeth in search of a body,” Michael I. Coates, an evolutionary biologist at the University of Chicago who was not involved in the study, tells the Guardian. “And here we have it, with thorough analyses of where it sits in the shark family tree and a good stab at its ecomorphology—how it fits into marine ecosystems of the Late Cretaceous.”

Scientists have known that Ptychodus roamed vast areas of the world’s oceans, emerging around 105 million years ago and going extinct roughly 30 million years later. Beginning in the early 1800s, fossils of the creatures were discovered in far-reaching locales—across the Americas, Asia, Europe and Africa.

This geographic diversity was a clue that these sharks were widespread, while the massive size of their teeth suggested these goliaths were able predators that, scientists thought, fed on seafloor-dwelling invertebrates.

Now, the six new specimens are rewriting paleontologists’ assumptions about Ptychodus.

A fossilized side view of Ptychodus, preserved in limestone found in a quarry in northeastern Mexico.
A fossilized side view of Ptychodus, preserved in limestone found in a quarry in northeastern Mexico. Vullo et al. / Proceedings of the Royal Society B, 2024

The sharks found in Mexico likely died about 93 million years ago, per the Guardian. One was a two-foot-long juvenile, two offered incomplete views of their skeletons, while another three fossils were entirely or nearly intact—with one offering scientists a full look at the creature’s musculature, fins, teeth and spine, as seen from the side. Though these specimens were less than ten feet long, the size of preserved teeth suggested some individuals could top 30 feet in length, per New Scientist’s Tom Leslie.

Based on this anatomy, the scientists think Ptychodus was a fast swimmer and hunted in the open water. Contradicting previous hypotheses, its diet likely consisted of hard-shelled turtles and ammonite prey, which required huge teeth that could crush and grind.

Because other marine predators in the Late Cretaceous hunted similar animals, it is possible Ptychodus went extinct after being out-competed for food, the study suggests.

“It’s almost the last jigsaw piece in putting together Cretaceous ecosystems,” Charles Underwood, a paleontologist at Birbeck, University of London, who was not involved in the study, tells New Scientist.

The team also concluded that Ptychodus likely belongs to the order of Lamniformes sharks, which also comprises many modern shark species—including great white, mackerel, megamouth, sand, goblin, basking and thresher sharks.

This relation, and the fact that more than one-third of all sharks and rays alive today are threatened with extinction, should serve as a lesson into the animals’ vulnerability, some scientists say.

Ptychodus provides us with a mirror that shows us what will happen to large apex predators such as the white shark if we, as their main competitor, do not rethink our actions,” Patrick L. Jambura, a paleontologist at the University of Vienna, tells the Guardian.

Editor’s Note, June 4, 2024: This story has been edited to remove an incorrect reference to the size of Ptychodus’ teeth.

Get the latest stories in your inbox every weekday.