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A large (5m) predatory ray-finned fish that lived in the late Cretaceous, X. audax had a pitbull-like snout that bristled with razor sharp teeth. Its habitat was the shallow sea that stretched across North America during that time. The rich biodiversity of the area likely provided X. audax with the resources and energy to maintain its size and metabolism, although it was not the apex predator of its time. These fossils provide insight into the complex food webs of the time, as X. audax specimens often have recent meals fossilized within their gut. It was not immune to predation itself, however, and so can also be found as recent meals of other hungry fish and reptiles.
Walker, MV, and Everhart, MJ. (2006). The Impossible Fossil – Revisited. Transactions of the Kansas Academy of Science, Vol. 109, Issue 1, pp. 87-96.
Bardack, D. (1965). Anatomy and evolution of Chirocentrid fishes. University of Kansas Paleontological Contributions, Article 10, pp. 88, pl 2.
Hay, OP. (1898). Observations on the Genus of Fossil Fishes Called by Professor Cope, Portheus, by Dr. Leidy, Xiphactinus. Zoological Bulletin, Vol. 2, No. 1, pp. 25-54.