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]

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]

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.

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

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]

• Ichthyodectiformes
• Ichthyodectidae
• Gillicus
• Leptolepis
• Ichthyodectes

1. ↑ ^{1.0 1.1} Vavrek, Matthew J; Murray, Allison M; Bell, Phil R. (2016). "Xiphactinus audax Leidy, 1870 from the Puskwaskau Formation (Santonian to Campanian) of northwestern Alberta, Canada and the distribution of Xiphactinus in North America". Vertebrate Anatomy Morphology Palaeontology.
2. ↑ Konishi, Takuya; Newbrey, Michael G.; Caldwell, Michael W. (2014). "A small, exquisitely preserved specimen of Mosasaurus missouriensis (Squamata, Mosasauridae) from the upper Campanian of the Bearpaw Formation, western Canada, and the first stomach contents for the genus". Journal of Vertebrate Paleontology.
3. ↑ "Fish Within a Fish at Sternberg Museum".
4. ↑ "Kansas Rep. Tom Sloan agrees to back X-fish as state's official fossil / LJWorld.com".
5. ↑ "State Fossils - Kansapedia - Kansas Historical Society".
6. ↑ "List of State Fossils - FossilEra".

• "Kansas Rep. Tom Sloan agrees to back X-fish as state's official fossil / LJWorld.com". .ljworld.com. Associated Press. 2010-10-26. Retrieved 2011-10-12.

• Carnegie Museum Archived 2004-11-14 at the Wayback Machine