It swam through the shallow waters of the ancient Western Interior Sea — which cleaved through North America — during the late Cretaceous period, noshing on smaller fish and seabirds. It had big teeth, in the realm of 3½ inches long, and a body in the neighborhood of 15 to 20 feet long.
Xiphactinus (zih-FACK-tih-nuss) was big and hungry, often gobbling down fish up to six feet long. It's not uncommon for Xiphactinus fossils to contain fossilized prey in the process of digestion. According to National Geographic, a 13-foot Xiphactinus could open its jaws wide enough to swallow a six-foot fish whole.
That's big, but not as big as the 18½-foot-plus Xiphactinus now on display at the Rocky Mountain Dinosaur Resource Center in Woodland Park. This fossil, RMDRC says, is the largest Xiphactinus ever discovered, having been excavated in Kansas by Mike Triebold, the owner of RMDRC. It took three professionals three years to reconstruct after the bones were carefully removed from a chalk bed in Kansas and shipped back to Colorado.
RMDRC is open daily, 9 a.m. to 6 p.m., Mondays through Saturdays, and 10 a.m. to 5 p.m., Sundays.