Species of
Xiphactinus were voracious predatory fish. At least a dozen specimens of
X. audax have been collected with the remains of large, undigested or partially digested prey in their stomachs. In particular, one fossil "
Fish-Within-A-Fish" specimen was collected by
George F. Sternberg with another, nearly perfectly preserved long ichthyodectid
Gillicus arcuatus inside of it. The larger fish apparently died soon after eating its prey, most likely owing to the smaller prey's struggling and rupturing an organ as it was being swallowed. This fossil is on display at the
Sternberg Museum of Natural History in
Hays, Kansas. Like many other species in the Late Cretaceous oceans, a dead or injured individual was likely to be scavenged by sharks (
Cretoxyrhina and
Squalicorax). The remains of a
Xiphactinus were found within a large specimen of
Cretoxyrhina collected by Charles H. Sternberg. The specimen is on display at the University of Kansas Museum of Natural History. Like modern tarpons,
Xiphactinus likely spent its juvenile stage of life in shallow seaway margins for protection and to utilize rich food resources, possibly rare in open marine water, though this needs confirmation due to the lack of shallow, nearshore deposits from the
Western Interior Seaway. The teeth of the juvenile specimen indicate that the diet of
Xiphactinus probably didn't change notably during its growth, implying that even the small specimens would have been fish-eating predators. == "Unicerosaurus" ==