A Case of Mistaken Sea Monster Identity

Re-analysis of Kansas fossils show they come from a newborn Tylosaurus, which were born without their tell-tale toothy snouts

Tylosaurus Bones
Christina Byrd

In what seems to be a bit of an “ugly duckling” scenario in which a juvenile looks nothing like its iconic adult counterparts, researchers have discovered that fossil fragments of a prehistoric sea monster found 30 years ago in Kansas were originally misidentified.

The remnants actually belonged to a newborn baby Tylosaurus, which belonged to a family of toothy, flippered marine reptiles called mosasaurs that lived in the world's oceans during the late Cretaceous period, or 66 to 100 million years ago, reports Laura Geggel at LiveScience. These sea-beasts were known for their long, pronounced snouts and could grow up to 42 feet in length.

Because the young Tylosaurus never got the chance to reach its gargantuan stature or develop its tell-tale elongated jawline, paleontologists mistook it for its smaller-bodied, less toothy mosasaur cousin, the Platecarpus, reports Helen Briggs at the BBC.

"The degree of snout development was nowhere near that of an adult," study author Takuya Konishi, a biologist at the University of Cincinnati, said to Briggs. "It was the ugly duckling that hadn't yet become the graceful swan."

Even though this Tylosaurus specimen was a baby, it was still about the size of Andre the Giant.

The fossil fragments were originally found in 1991 in western Kansas in a fossil rich geologic formation called the Smoky Hill Chalk Member, which exists where the Western Interior Seaway—a prehistoric inland sea that divided the North American continent—once was. At the time, paleontologists thought the tiny pieces were the remains of a short-snouted Platecarpus, which could only grow up to 20 feet long.

The fossil was at first misidentified because the fragments—including part of a snout, teeth, jaw and skull—don’t really look like a Tylosaurus. Starkly lacking was the long, toothy snout that defines the animal. Konishi first examined the fragments back in 2004 while working on his master’s degree. He was inspired to take a second look by recent advances in how mosasaurs, which all look very similar, are identified. He then realized that the fossil was from a 7-foot baby Tylosaurus, which likely died soon after birth, according to the new study published in the Journal of Vertebrate Paleontology.

“Having looked at the specimen in 2004 for the first time myself, it too 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,” he says in a statement. “For those 10 years or so, I had believed too that this was a neonate of Platecarpus, a medium-sized (5-6 meters) [16-20 feet] and short-snouted mosasaur, not Tylosaurus, a giant (up to 13 meters) [42 feet] mosasaur with a significantly protruding snout.”

Konishi and his team were able to identify the baby Tylosaurus using the shape of the animal’s braincase, the spacing of its teeth and a question-mark shaped bone in the back of its jaw called a quadrate.

The finding means the toothy swimmers must have developed their iconic snouts quickly between birth and their juvenile stage, since other juvenile Tylosaurus fossils do sport big noses. It also raises the possibility that early Tylosaurus species did not have the toothy snout after all.

“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,” Konishi says in the statement.

While Tylosaurus was huge, and the mosasaur in Jurassic World was depicted at twice its actual size, it was no match compared to the largest sea monster to swim the seas. Earlier this year paleontologists revealed that ichthyosaur fossils found on an English beach could have come from a creature up to 85 feet long, though that is still dwarfed by the modern blue whale, which can reach 100 feet in length.

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