Xiphactinus

Xiphactinus (from Latin and Greek for "sword-ray") was a large, 4.5 to 5 m (15 to 20 feet) long predatory bony fish that lived in the Western Interior Sea, over what is now the middle of North America, during the Late Cretaceous. Skeletal remains of Xiphactinus have come from Kansas, Alabama, and Georgia in the United States, as well as Europe anοd Australia. This monster grew up to 5–6 metres (16–20 ft) in length, and resembled a giant, fanged tarpon.^[1]

Xiphactinus Temporal range: Cretaceous
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	†Ichthyodectiformes
Family:	†Ichthyodectidae
Genus:	†Xiphactinus Leidy, 1870
Type species
†Xiphactinus audax Leidy, 1870

Description

Physical appearance

Above all else, Xiphactinus was a great swimmer, able to speed towards or away from virtually anything else in the seas of the time. It may have been able to leap above the waves at times to help dislodge parasites from its skin. It was not however immune from attack. If injured, its large size meant it was easy to spot and could become prey for sharks, mosasaurs, and other Xiphactinuses.

One fossil described from the Puskwaskau Formation has large, thecodont teeth that are circular in cross section and lack any carinae, and are highly variable in their overall size. This fossil is the first diagnostic material of X. audax from Alberta, and extends the range of the species by over a thousand kilometres.^[1]

The famous Fish-within-a-Fish fossil: Xiphactinus with a Gillicus inside its belly.

Fish-within-a-Fish

One iconic fossil called the "Fish-Within-A-Fish" specimen was collected by George F. Sternberg with another, nearly perfectly preserved 1.9 metres (6.2 ft) long ichthyodectid Gillicus arcuatus inside of it. This fossil is on display at the Sternberg Museum of Natural History in Hays, Kansas.^[2]

In this fossil, a Gillicus is inside a Xiphactinus. The head of the Xiphactinus faces left and the skeleton and fins are visible. The Gillicus is underneath the bones in the center,^[3] hence the name.

Mounted skeleton of X. audax at the American Museum of Natural History

Species

• †Xiphactinus audax Leidy, 1870 (type)
• †Xiphactinus vetus Leidy, 1856

In popular culture

State fossil

Restoration of X. audax

In October 2010, Kansas House Rep. Tom Sloan announced that he would introduce legislation to make Xiphactinus audax, or "X-fish", the state fossil of Kansas.^[4] Ultimately, Tylosaurus was chosen instead.^[5][6]

Related pages

• Ichthyodectiformes
• Ichthyodectidae
• Gillicus
• Leptolepis
• Ichthyodectes

A Xiphactinus eating a Gillicus