Patrones de reemplazamiento biótico en cocodrilos modernos durante el Cretácico Superior

Abstract

The Late Cretaceous crocodylomorph record is revised in detail in order to examine the biotic replacement that characterises the appearance of the members of the Crocodylia clade. The percentages of crocodylian and non-crocodylian genera have been estimated by chronostratigraphic stage and by continent. The results show that there are a higher proportion of non-crocodylians genera (71%) in the Late Cretaceous. However, the percentage of Crocodylia increases from 6% in the Cenomanian - Santonian to 22% in the Campanian - Maastrichtian interval. Crocodylia have a pattern of expansive radiation, without involving a geographic shift of non-crocodylians crocodylomorph. The chronostratigraphic distribution of the crocodylian genera is mostly restricted to Campanian-Maastrichtian localities. Crocodylians have a non-uniform spatial distribution among continents. Two different patterns are distinguished: 1) Europe plus North America, characterised by a high proportion of Crocodylia, exceeding 50% of the total number of genera, and 2) Asia, South America and Africa, all of which have similar proportions, in which the crocodylians form less than 15% of the crocodylomorph assemblage. A large-scale expansive radiation and diversification of crocodylians is postulated for Europe and North America at the uppermost Cretaceous. The bulk of the biotic replacement occurs in the continental realm. The absence of continental members of Crocodylia in Asia, Africa and South America is significant because non-crocodylians are otherwise well-documented throughout the Upper Cretaceous. Taxonomic dissimilarity between continents is so high that no continental genera are shared between continents.