The Cretaceous world

The Cretaceous Period is notable for documenting the evolutionary success of dinosaurs as dominant land animals. The end of the Cretaceous provides abundant evidence of this, particularly in North America. Novacek (2007) refers to the terminal Cretaceous as a “Dinosaur Camelot,” which poignantly invokes lost glories in forgotten landscapes. Flying and aquatic reptiles were also dominant at this time. The rise of angiosperms or flowering plants also occurred during the Cretaceous. As related later in this chapter, at least one researcher, Robert Sussman, believes that the origin of primates was linked to the rise of angiosperm plants. The paleogeography of the earth during the Late Cretaceous and at the Cretaceous/Tertiary boundary is well known (Figures 7.1 and 7.2)

Morphological, molecular, and genetic data have been used to study the relationships of living and fossil placental mammal orders. The plate tectonic separation of Africa and South America that began about 100 mya has been used to explain the divergence of placental mammal orders. However, a recent analysis using both morphology and molecular evidence refutes the notion that the creation of the Atlantic Ocean had anything to do with the divergence of placental mammal orders (Asher et al., 2003).