Fossilized remains of a Cretaceous-era sea monster discovered in Mesa County |

Fossilized remains of a Cretaceous-era sea monster discovered in Mesa County

Caitlin Row

The fossilized remains of an elasmosaurid plesiosaur — a carnivorous marine reptile with flippers, thought to be the length of a five-story building — was recently discovered near the Bookcliffs, northwest of the Grand Junction Regional Airport.

“Not a lot of vertebrates have been found (at that location) in the past,” Dinosaur Journey Museum Curator of Paleontology John Foster said. “There’s been a lot of squid relatives, mussels and clams — things like that — found along that formation along the river, and there are oysters found in that area.”

Though finding plesiosaur fossils isn’t uncommon across the globe, Foster noted that this type of animal hasn’t often been discovered in the Grand Valley’s Mancos Shale area, “which is the marine unit most of the Grand Valley is sitting on.”

The area is not a bone bed, rather discoveries tend to be of isolated fossils scattered throughout.

“In marine units, it’s common to have findings of single animals that sink to the bottom and get buried,” Foster added.

According to Foster, the remains of the fossilized elasmosaurid plesiosaur discovered near the Bookcliffs appears to be from a 40-foot-long reptile, and it’s been dated back to the late Cretaceous Period, 75 million years ago.

“It’s neat to know that there was such a huge, swimming reptile in this area back then, near the end of the time of dinosaurs,” he continued. “They were a contemporary of dinosaurs, when this guy was swimming the seas so close to Grand Junction.”

Foster’s elasmosaurid plesiosaur is only one of four found on the Western Slope of Colorado over the years, and it’s definitely the biggest.

“So far we’ve gotten 10 vertebrate out of this site,” he said, “and a rib. We want to go back out there this fall and we’re hoping that we can find some other elements. The head of course would help the most, and more vertebrate or parts of flippers.”

Finding a preserved head of an elasmosaurid plesiosaur is fairly rare: “We don’t usually hold our breath for the skull,” Foster said.

The skull is actually relatively small in comparison the rest of the marine reptile’s body, and this oceanic beast likely dined on fish.

Fruita’s Dinosaur Museum holds a permit for fossil collection with the Bureau of Land Management.

“We hope to have this guy on display (in 2014) for everybody to see,” Foster said.

For more information about Western Colorado’s Dinosaur Journey Museum in Fruita, call 970-858-7282 or visit

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