Adaptive Radiation of Mammalian Orders

At the end of the Cretaceous period 65 MYBP [Million Years Before Present], only two lineages of Eutherian mammals were present: insectivorous Protoeutheria and hoofed Condylarthra. Non-eutherian Marsupialia [far left] and Monotremata [far right] were present, as well as Multituberculata, a now-extinct group resembling rodents. Following the disappearance of dinosaurs at the K/T [Cretaceous / Tertiary ] boundary, there was a rapid evolution of new mammalian types. By the middle of the Eocene epoch (45 MYBP), most of the twenty or so present-day mammalian orders are identifiable, including forms as diverse as Chiroptera [bats] descended from Protoeutheria and Cetacea [whales] descended from Condylarthra. This rapid evolution of morphological and taxonomic diversity is an example of an adaptive radiation.

Figure after ©1966 by AS Romer; Text material ©2005 by Steven M. Carr