Creature of the Week #24: Xiphactinus

Xiphactinus (meaning "sword-ray") was one of the largest sea creatures of the Late Cretaceous and is considered to have been amongst the top sea predators of its time. It lived aproximately seventy million years ago in the Western Interior Seaway, a vast shallow sea that stretched across what is now center of the North American continent. A member of the teleost fish family (bony fishes), a number of specimens of Xiphactinus have been unearthed, the first being found in Kansas in the 1850s. While a powerful predator, it was not at the very top of the Cretaceous food chain, as fossils of prehistoric sharks such as Squalicorax and Cretoxyrhina have been found to occasionally contain Xiphactinus remains.



Xiphactinus had a large body that was between fifteen to twenty feet long with more than 100 vertebrae making up its backbone. Its compressed, flattened face combined with an upturned jaw and large fang-like teeth gave it a highly distinctive bulldog-like expression. The jaw was very mobile, capable of opening extremely wide to take in large-sized prey, although the teeth may have been used to strike or impale prey during the initial attack. Its long pectoral fins held out by solid bony fin rays giving them an almost wing like appearance. A deep and forked tail was attached to the body at a narrow base. All of these feature indicate that Xiphactinus was a fast, powerful swimmer and a very efficient predator.

Xiphactinus had a voracious appetite and usually swallowed other fish whole, as numerous fossils have been found with very large fish inside the body cavity. One of the most famous fossils of all time is the amazing "fish within a fish" specimen. Discovered by George Sternberg in 1952 , it revealed a fourteen foot Xiphactinus that contained the almost completely intact six foot long remains of a fish called Gillicus. This was the last meal that that particular Xiphactinus ever ate and its gluttony was probably was the cause of its downfall. Paleontologists speculate that the Xiphactinus died right after swallowing the fish, because its still-living prey managed to puncture its stomach.



Xiphactinus became extinct near the very end of the Cretaceous as the Western Interior sea begain to recede from North America.