“T. rex of the Ocean”: Giant 13-Meter Tylosaurus rex Ruled the Seas 80 Million Years Ago!

Paleontologists have formally named Tylosaurus rex — the “T. rex of the ocean” — a colossal new species of mosasaur that dominated the Western Interior Seaway 80 million years ago. At an estimated 13 meters (43 feet) long, it was one of the largest marine reptiles of its time and the biggest Tylosaurus ever discovered in North America.

The near-complete skeleton, including a mᴀssive 1.6-meter skull, was recovered from the marine shales of the Niobrara Formation in Kansas and described in a June 2026 Journal of Vertebrate Paleontology paper. Its enormous, robust skull, interlocking serrated teeth, and powerful jaws were built for “grip-and-tear” predation on sharks, plesiosaurs, and other mosasaurs. CT scans reveal a reinforced braincase and hyper-robust cervical vertebrae, confirming it was a top-tier macropredator.

Lead author Dr. Thomas Rivera states: “This was not just a bigger Tylosaurus; it was a specialized apex predator that sat at the absolute summit of the marine food chain.” The animal lived during the early Campanian stage, when the seaway was at its widest, teeming with prey. Its size and anatomy suggest it could tackle animals larger than itself, possibly including other large mosasaurs.

The discovery cements Kansas and the Niobrara Formation as the world’s richest window into giant marine reptiles of the Late Cretaceous. As biomechanical modeling continues, Tylosaurus rex promises to show how these sea monsters achieved such enormous size and dominance before the end-Cretaceous extinction wiped them out. The true king of the ancient ocean has finally been named.