level in a diverse pelagic ecosystem during the Cretaceous. Most of these predators included large marine reptiles, some of which already occupied the highest trophic level when Cretoxyrhina first appeared. During the Albian to Turonian, about 107 to 91 Ma, Cretoxyrhina was contemporaneous and coexisted with Mid-Cretaceous pliosaurs. Some of these pliosaurs included Megacephalosaurus, which attained lengths of . By the Mid-Turonian, about 91 Ma, pliosaurs became extinct. It is thought that the radiation of sharks like Cretoxyrhina may have been a major contributing factor to the acceleration of their extinction. The ecological void they left was quickly filled by emerging mosasaurs, which also came to occupy the highest trophic levels. Large mosasaurs like Tylosaurus, which reached in excess of in length, may have competed with Cretoxyrhina, and evidence of interspecific interactions such as bite marks from either have been found. There were also many sharks that occupied a similar ecological role with Cretoxyrhina such as the cardabiodontids Cardabiodon and Dwardius, the latter showing evidence of direct competition with C. vraconensis based on intricate distribution patterns between the two. A 2010 study by paleontologists Corinne Myers and Bruce Lieberman on competition in the Western Interior Seaway used quantitative analytical techniques based on Geographical information systems and tectonic reconstructions to reconstruct the hypothetical competitive relationships between ten of the most prevalent and abundant marine vertebrates of the region, including Cretoxyrhina. Their calculations found negative correlations between the distribution of Cretoxyrhina and the three potential competitors Squalicorax kaupi, Tylosaurus proriger, and Platecarpus spp.; a statistically significant negative correlation implies that the distribution of one species was affected due to being outcompeted by another. However, none of the relationships were statistically significant, which instead indicates that the trends were unlikely the result of competition. Extinction The causes of the extinction of Cretoxyrhina are uncertain. What is known is that it declined slowly over millions of years. Since its peak in size during the Coniacian, the size and distribution of Cretoxyrhina fossils gradually declined until its eventual demise during the Campanian. Siverson and Lindgren (2005) noted that the age of the youngest fossils of Cretoxyrhina differed between continents. In Australia, the youngest Cretoxyrhina fossils were dated approximately 83 Ma during the Santonian, while the youngest North American fossils known at the time (which were dated in the Early Campanian) were at least two million years older than the youngest fossils in Europe. The differences