Xiphactinus life

Xiphactinus (Sword Ray), also known as the "X-fish", is a genus of giant predatory marine bony fish that lived in oceans all over the world 100.5 – 66 million years ago, from the Cenomanian to the Maastrichtian Stage of the Late Cretaceous Period. Prehistoric Planet depicts the type species, Xiphactinus audax, which succeeded the earlier, smaller Xiphactinus vetus. The largest known bony fish of the Late Cretaceous Period, Xiphactinus resembles a massive, fanged tarpon, reaching over 5 - 6 meters (16 - 20 feet) in length and 1.3 - 1.43 metric tons (1.43 - 1.58 short tons) in mass. It had a large mouth, fittingly large teeth, and large nostrils for easily detecting the scent of prey in the ocean. With all these in mind, Xiphactinus is reasonably believed to be an endothermic or mesothermic animal (that is also possibly poikilothermic), able to maintain a core body temperature higher than its surroundings with the help of its large size (gigantothermy), giving it the energy to speed up for short periods of time to pursue or ambush prey. This can be seen in the second segment of Oceans, where several Xiphactinus are able to grab and devour several Hesperornis. Given their size and metabolic differences, however, the birds (which are "warm-blooded" to a greater degree) proved to be more agile than the predators, allowing those not caught off-guard by the sudden attacks to escape the voracious hunters. The most commonly-stated speed estimate for Xiphactinus is 60 kilometers (37.3 miles) per hour.