Xiphactinus
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| Xiphactinus Fossil range: Late Cretaceous |
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 Xiphactinus
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| Xiphactinus audax Leidy, 1870 |
Xiphactinus audax (from Latin and Greek for "audacious sword-ray") was a large, 4.5 to 5 m (15 to 20 feet) long predatory bony fish that lived in the Niobraran Sea, in what is now North America, during the Late Cretaceous. When alive, the beast would have resembled a gargantuan, fanged tarpon (to which it was, however, unrelated).[1] A junior synonym of the species is Portheus molossus.[2] Skeletal remains of Xiphactinus have come from Kansas, Alabama, and Georgia.
[edit] Palaeobiology
Despite being a fierce predator, many remains have been found within skeletons of the mosasaur Tylosaurus proriger. X. audax was also prey to Cretoxyrhina, as remains have been also been found inside of this shark's fossils, as well.
Despite being preyed on by sharks and mosasaurs, X. audax was a voracious predator in its own right. Numerous fossils have been found with large, undigested prey in their gullets or stomachs. In particular, one 15 foot fossil specimen was found by George F. Sternberg with another, perfectly preserved 6 foot long ichthyodectid Gillicus arcuatus, inside of it. The beast died immediately after eating its relative, most likely due to its prey 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.[3]
Virtually nothing is known about their larval or juvenile stages. The smallest fossil specimen of X. audax is a fragment of a premaxilla bone that came from an individual estimated to be about 12 inches long.[4]
The species went extinct when the Niobraran Sea began to close up and dry out during the Late Cretaceous. The other ichthyodectids perished in the Cretaceous-Tertiary extinction event.
An incomplete skull of what may be a new species of Xiphactinus was found in 2003 in the Czech Republic, in a region called Sachov next Borohradek, by student Michal Matejka.
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