Species of Xiphactinus were voracious predatory fish. At least a dozen specimens of X. audaxhave been collected with the remains of large, undigested or partially digested prey in their stomachs. In particular, one 13 feet (4.0 meters) fossil specimen was collected by George F. Sternbergwith another, nearly perfectly preserved 6 feet (1.8 meters) long ichthyodectid Gillicus arcuatus inside of it. The larger fish apparently died soon after eating its prey, most likely owing to the smaller fish prey's struggling and rupturing an organ as it was being swallowed. This fossil can be seen at the Sternberg Museum of Natural History in Hays, Kansas.
Like many other species in the Late Cretaceous oceans, a dead or injured individual was likely to be scavenged by sharks (Cretoxyrhina and Squalicorax). The remains of a Xiphactinus were found within a large specimen of Cretoxyrhina collected by Charles H. Sternberg. The specimen is on display at the University of Kansas Museum of Natural History.
Virtually nothing is known about the larval or juvenile stages. The smallest fossil specimen of X. audax consists of a tooth bearing premaxilla and lower jaws of an individual estimated to be about 12 inches (30 cm) long.
The species and all other ichthyodectids became extinct near the end of the Late Cretaceous – see Cretaceous–Paleogene extinction event.
An incomplete skull of what may be a new species of Xiphactinus was found in 2002 in the Czech Republic, in a small town called Šachovnext to Borohrádek city, by 16 years old student Michal Matějka.
In July 2010 the bones of a Xiphactinus were discovered near Morden, Manitoba, Canada. The specimen is about six metres long and was found with the flipper of a mosasaur between its jaws.
In Pop Culture
- They featured in the third movie in the BBC Walking with Dinosaurs Special: Sea Monsters Trilogy. In it, they were first seen joining in a feeding frenzy with some prehistoric sharks, possibly Squalicorax. Then later on, a Xiphactinus was seen leaping out of the water to devour a pterosaur, but misses. Towards the end of the movie, it was shown harassing both Nigel Marven and an Archelon, before, presumably, being scared away by a mosasaur pack.
- In October 2010, Kansas House Rep. Tom Sloan (R-Lawrence) announced that he would introduce legislation to make Xiphactinus audax, a.k.a. the "X-fish", the state fossil of Kansas.
- Xiphactinus also appears in both the Film & Video Game of National Geographic's Sea Monsters A Prehistoric Adventure.
- It appears in Prehistoric Assassins: Blood in the Water.
- Xiphactinus is a limited edition creature in the Aquatic Park section of Jurassic Park: Builder.
- Xiphactinus was added to Jurassic World: The Game as a creatable aquatic animal on the March 16, 2016 update.
- Xiphactinus also appeared in River Monsters, labelled "Prehistoric Terror".
- It also appears at the end of the 2003 TMNT Episode Return of Savanti, Part 2 with the Time Scepter in its belly.
- In concept art for Jurassic Park: The Game, a Xiphactinus skeleton was to be on display inside the Marine Facility's rotunda, but it is absent from the finished game.