Five-metre-long sea monster ruled ancient Kansas ocean
About 80 million years ago, when dinosaurs still walked the Earth, a five-metre sea monster called a mosasaur cruised the ancient ocean that once covered western Kansas, snagging prey with its slender, tooth-lined snout. Palaeontologists discovered a fossil of this beast in the 1970s, but they had difficulty classifying it, so it ended up stored with other mosasaur specimens in the Platecarpus genus at Fort Hays State University’s Sternberg Museum of Natural History (FHSM) in Kansas.
Recently, researchers revisited the enigmatic fossil – pieces of a skull, jaw and a few bones from behind the head – and found that the reptile didn’t belong in the Platecarpus genus. Rather it was a close relative of a rare mosasaur species known from just one specimen. The newly described species, formerly known as specimen FHSM VP-5515 and now named Ectenosaurus everhartorum, is the second known species in the Ectenosaurus genus. The only other known species is Ectenosaurus clidastoides, which was described in 1967.
E. everhartorum’s head was about 0.6 metres long, and like E. clidastoides, E. everhartorum had a snout that was narrow and elongated compared with those of other mosasaurs. “It’s a kind of skinny snout for the agile, speedy snapping of fish, rather than biting into something hard like turtle shells,” said Takuya Konishi, a vertebrate palaeontologist and assistant professor at the University of Cincinnati. The narrowness of the jaw and of a bone at the top of the head hinted that VP-5515 belonged in the Ectenosaurus genus, even though the fossil was about 500,000 to 1 million years younger than the E. clidastoides specimen, Konishi said. But in some ways the skull wasn’t Ectenosaurus-like at all. For example, it lacked a bony bump at the end of its snout. The snout on VP-5515 was also shorter than the one on E. clidastoides. “We knew it was a new species, but we didn’t know if it was an Ectenosaurus or not,” Konishi said. “To answer that puzzle, we were eventually able to find another feature where the jaw joint was, at the back end of the lower jaw.” There the researchers detected a small notch that didn’t appear in any mosasaur species – except one.
“That little depression turned out to be a newly discovered consistent feature for the genus Ectenosaurus,” Konishi said. “You have this Ectenosaurus united by the little notch at the end of the lower jaw, but then it’s consistently different at the level of the species from the generic type – that is to say the first species assigned to the genus.”
One lingering question about Ectenosaurus is why this genus is so poorly represented among mosasaur fossils from western Kansas. To date, palaeontologists have uncovered more than 1,800 mosasaur specimens at the site of the former inland sea. But for now the entire Ectenosaurus genus is represented by just two fossils, one for each species. “That’s very strange,” said Konishi. “Why is it so rare for a mosasaur where you have hundreds of Platecarpus from the same locality? Does that mean they were living near the shore, or were they living farther south or farther north? We just don’t know.”