Giant-Headed Sea Monster Found in Kansas Museum

megacephalosaurus sea monster picture

Thanks to some creative casting some 60 years ago, the fossil of an aquatic reptile in a Kansas museum was only recently found to be that of a totally different, much larger, and probably fiercer, sea monster.

The newly discovered creature is most notable for its giant — almost disproportionately large — head with rows of arrow-sharp teeth, earning it the name Megalocephalosaurus, or big-headed reptile.

Having reached up to 9 meters in length, it was likely one of the most formidable predators in the ancient sea that  bisected North America some 90 million years ago.

Artist’s rendering of Megacephalosaurus eulerti on the hunt (Kenneth Carpenter/USU Eastern)

Its discovery was long in the making, however, because its most distinguishing feature had long been hidden from view — intentionally.

In 1950, the remains of a giant plesiosaur — not a dinosaur, but an ancient marine reptile — were found on a ranch in Russell County, Kansas.

Paleontologists diagnosed them as belonging to the ocean-dwelling reptile Brachauchenius lucasi, itself a forbidding predator that had been found elsewhere in Kansas some 65 years earlier.

But when the specimen was ready to be put on display, curators decided to mount its wonderfully intact skull on its side in a bed of colored plaster, to make it look like it was still entombed in rock.

Megacelphalosaurus’ skull is nearly 5 feet long (USU)

For half a century it thus sat on view in Kansas’ Sternberg Museum of Natural History, shown off as one of the best specimens of B. lucasi ever found.

Until recently, when a paleontologist at the Denver Museum, Dr. Ken Carpenter, came across archival photographs of the fossil before it was cast in fake rock.

“When we looked at the images we realized that the roof of the mouth was very different from what we had assumed,” Carpenter recently told Utah Public Radio.

“I arranged to have the specimen brought out to me and we removed it from the big block of plaster that it had been embedded in.

“Once we removed it and could actually look at the underside and the roof of the mouth in detail, we realized we had a totally different animal.”

The head, Carpenter’s team discovered, was 1.5 meters long, some 50% larger than that of B. lucasi, and some of its traits, including its palate, the arrangement of the skull bones, and its ribs, were unlike that of any other known creature.

Given its fearsome features, Carpenter said Megacephalosaurus was likely an apex hunter of the North American Inland Sea — which once covered what’s now the Midwest — describing the reptile as the orca of its time.

“It was top predator,” he told UPR.


• “USU paleontologist helps discover ancient reptile” by Matt Jensen, Utah Public Radio

• “A new Cretaceous Pliosaurid (Reptilia, Plesiosauria) from the Carlile Shale (middle Turonian) of Russell County, Kansas,” Journal of Vertebrate Paleontology, Volume 33, Issue 3, 2013

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