Smallest Tylosaurus Fossil Ever Found Unearthed In Kansas

The fossil suggests that these ancient marine lizards hunted in a similar way to killer whales.

Mosasaur fossil.
Barbara Ash / Shutterstock

The fossil suggests that these ancient marine lizards hunted in a similar way to killer whales.

A paleontological discovery made in Kansas back in 1991 is now being hailed as the smallest Tylosaurus mosasaur ever uncovered. Unearthed from a Late Cretaceous rock formation dubbed Niobrara Chalk, the fossil is described in a study published yesterday in the Journal of Vertebrate Paleontology.

While paleontologists have known about this find for almost three decades, the fossil was only recently identified as a Tylosaurus — a large marine lizard belonging to an extinct group of creatures known as mosasaurs.

This is because the fossil looks nothing like other Tylosaurus remains, reports

An Unusual Fossil

Although the Kansas fossil was clearly a mosasaur, researchers had trouble fitting it into the correct species. The fossil was originally mistaken for a Platecarpus, another type of mosasaur.

The reason for the confusion was the fact that, unlike most Tylosauruses, this fossil doesn’t have a long snout — the trademark feature of the species.

After re-examining the specimen and comparing it to fossils of young marine lizard from related species — such as T. nepaeolicus and T. proriger, which were developed enough to sport an identifiable nose — the study authors were finally able to properly identify the bones.

The team arrived at the conclusion that fossil belonged to a newborn Tylosaurus that died before having the chance to grow out its snout.

“Having looked at the specimen in 2004 for the first time myself, it took me nearly 10 years to think out of that box and realize what it really was — a baby Tylosaurus yet to develop such a snout,” said study lead author Takuya Konishi, a professor in the Department of Biological Sciences at the University of Cincinnati, Ohio.

The Feared Tylosaurus

Tylosaurus mosasaur could grow to be up to 46 feet (14 meters) long and prowled the oceans of the Late Cretaceous hunting for plesiosaurs, sharks, fish, seabirds, and even other mosasaurs. According to National Geographic, Tylosaurus was a prolific killer and “the deadliest hunter of the ancient seas.”

3D illustration of a Tylosaurus mosasaur.
A 3D illustration of a ‘Tylosaurus mosasaur.’ Michael Rosskothen / Shutterstock

These predatory reptiles are closely related to modern-day monitor lizards and snakes, and were brought to their demise by the Chicxulub asteroid that wiped out the dinosaurs 66 million years ago.

The most striking physical feature of Tylosaurus was its “significantly protruding snout,” explains Konishi.

Meanwhile, the much smaller Platecarpus, which only grew to half the size of its giant cousin, was a short-snouted mosasaur — the very reason why paleontologists first suspected that the Kansas fossil was a Platecarpus.

Computer-generated image of a Tylosaurus mosasaur and a pterosaur.
Computer-generated image of a ‘Tylosaurus mosasaur’ and a pterosaur. Michael Rosskothen / Shutterstock

While the recent discovery has brought to light a very intriguing Tylosaurus fossil, it also revealed some captivating facts about these long-extinct reptiles.

The Smallest ‘Tylosaurus’ Ever Discovered

At just one-sixth the size of a full-grown adult, the Kansas fossil is the smallest Tylosaurus that paleontologists have ever set eyes on.

The remains dug out of Niobrara Chalk — particularly the lower Santonian portion of the rock formation, dating back between 86 million and 83 million years ago — represent only a partial fossil. The discovered bones of the smallest Tylosaurus include a partial braincase, a partial snout with teeth and tooth bases, and a section of upper jaw — also with tooth bases.

Judging by the size of the bones, paleontologists estimate that the skull of the newborn Tylosaurus was about a foot long (30 centimeters). By comparison, the skull of an adult measured almost six feet (1.8 meters).

The discovery of a baby Tylosaurus lacking the species’ iconic long snout has led scientists to surmise that the prehistoric sea lizards developed their pointy nose quite quickly, sometime between birth and reaching juvenile state.

This, in turn, revealed something unexpected about the species, remarked Konishi.

“As individual development and evolutionary history are generally linked, the new revelation hints at the possibility that Tylosaurus adults from much older rock units may have been similarly short-snouted, something we can test with future discoveries.”

Hunting Like Killer Whales

Another surprising discovery to stem from the re-examination of the Kansas fossil was that mosasaurs may have displayed a hunting behavior very similar to that of killer whales, notes Science Daily.

According to Konishi, these marine lizards probably subdued their prey by ramming it with their bony snouts — just like killer whales do.

“Killer whales don’t hunt big prey by biting. They hunt by ramming and tearing them apart after the prey is weak,” Konishi said. “And their snout is conspicuously protruding.”

The paleontologist came up with this theory after taking a closer look at the snout of the baby Tylosaurus. As he explains, the snout of this species ended in a bony protrusion called a rostrum, which extended out from the face.

This particular feature is also found in killer whales and may have served a very specific purpose, namely to shield the animal’s front teeth as it slammed prey with its snout.

“When orcas hunt dolphins and small whales, they subdue them by ramming them. And when you look at them, you see they have a protruding snout as well,” explained Konishi.