85 million years ago, North America was divided in two by the Western Interior Seaway, an inland sea that separated Laurasia and Appalachia. This sea was shallow and warm, the perfect conditions for a new kind of predator that called these waters home: Xiphactinus, the largest known fish of the Cretaceous Period.

These massive fish measured five meters long, with a half-moon shaped fin for added speed. Their sharp teeth appeared fang-like, and they were even likely warm-blooded, their endothermy powering their strong bodies. With tools like there, Xiphactinus hunted down just about anything that came in its way, including members of its own family like Gillicus arcuatus.

This specimen is a showcase Xiphactinus fossil, which was once part of the fearsome Cretaceous fish. Bones like these fit together to form the inner structure of these massive aquatic beasts. Each specimen ships in a sturdy carton and comes complete with an informational card, which serves as certificate of authenticity.

You can explore all or our showcase Xiphactinus fossils in the collection below!

Xiphactinus is one of the largest predatory bony fish across the fossil record, most often found in North America where the Western Interior Seaway once split the continent. They lived during the Late Cretaceous Period, from 85 to 65 million years ago, which based on their location would have put them face to face with other aquatic creatures of the dinosaur age like Elasmosaurus and Mosasaurus.

Specimens from Kansas’s Niobrara Formation, the best-known source of the fish, top out at over 5 meters, while a few isolated tooth fossils suggest even larger specimens. Beyond North America, Xiphactinus specimens can be found across Europe and in South America, wherever shallow water could be found for these adept hunters. Despite this vast distribution, only two Xiphantinus species are known: the type species Xiphactinus audax and Xiphactinus vetus, both discovered in Kansas by paleontologist Joseph Leidy in the mid-nineteenth century.

Being a part of the bony fish class (or osteichthyans), Xiphactinus specimens fossilize particularly well and there are many complete skeletons known. Inside of some of these specimens can be the remains of smaller fish fossilized within. Most famous is the "Fish-Within-A-Fish" specimen, with the fossilized remains of an entire Gillicus arcuatus preserved with a Xiphactinus audax, direct evidence of the fish’s predatory prowess.

Both Xiphactinus and Gillicus were a part of the same family of predatory fish: the Ichthyodectiformes. These ray-finned fish were abundant in the Western Interior Seaway, using their gigantic stature to dominate other fish. Gillicus was smaller than Xiphactinus at two meters, but boasted some of the same predatory attributes as its larger cousin. The family was largely wiped out in the K/Pg extinction, confining these impressive attributes to the fossil record.

The fish’s well-preserved anatomy also gives insight into its hunting behavior. Xiphactinus appeared much like modern tarpons but with a half-moon-shaped tail fin and large fangs. With these attributes, Xiphactinus could quickly close the gap on its prey before closing its teeth around an unlucky fish. These caniniform teeth were present in juvenile specimens, suggesting even their young were adept hunters.

This body plan and the high energy levels needed for predation lends evidence to the theory that Xiphactinus was endothermic, or warm-blooded. This is because its large size would greatly slow metabolic rates if Xiphatinus was ectothermic, or cold-blooded. Xiphantinus' body plan supports this theory as does its habitat in the shallow Western Interior Seaway, an environment conducive to endothermic energetic fish.