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100 Million Years of Land Vertebrate Evolution: The Cretaceous-Early Tertiary Transition

Michael J. Novacek
Annals of the Missouri Botanical Garden
Vol. 86, No. 2 (Spring, 1999), pp. 230-258
DOI: 10.2307/2666178
Stable URL: http://www.jstor.org/stable/2666178
Page Count: 29
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100 Million Years of Land Vertebrate Evolution: The Cretaceous-Early Tertiary Transition
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Abstract

A critical time interval for vertebrate evolution-between 100 and 112 million years in duration-spans the beginning of the Cretaceous period to the late Eocene epoch of the Cenozoic. This interval encompasses the appearance in the Cretaceous of many of the modern vertebrate groups that persist today, the extinction event at the Cretaceous-Tertiary (K/T) boundary, and the restructuring of the vertebrate megafauna dominated by mammals in the Paleocene and Eocene. Cretaceous turnover in the dinosaur fauna has been tied to the radiation and diversification of angiosperms, but these correlations do not apply to all continental regions represented by a fossil record. The Cretaceous also marks the emergence and radiation of certain groups of mammals, birds, lizards, and freshwater fishes. Reconstructions, however, that push back the diversification of modern lineages of birds and mammals (groups that include extant representatives) to the Early or middle Cretaceous are not supported by the fossil record. Despite the severity of the Cretaceous-Tertiary (K/T) extinction event of 65 million years ago, effects on vertebrates are strikingly selective, with a number of groups, including actinopterygians (ray-finned fishes), multituberculate mammals, eutherian mammals, turtles, lizards, champsosaurs, and crocodiles surviving across the K/T boundary. Subsequent to the K/T event, the basic organization and dynamics of the larger vertebrate fauna were radically transformed. Of general evolutionary interest is the protracted "rebound" of the larger vertebrate fauna and the nature of its controlling factors. The loss of the non-avian dinosaurs meant a loss of larger herbivorous browsers not replenished for some millions of years into the Paleocene. Diversification in the smaller mammal fauna shows a new emphasis on frugivory and granivory. Some of the modern groups of mammals first appear in the late Paleocene-early Eocene. Subsequent climate and habitat changes coincide with the radiation of large herbivorous mammals such as perissodactyls and artiodactyls. The coevolutionary relationships of the terrestrial mammalian megafauna and the changing flora likely promoted the spread of more open habitals that characterized the later Cenozoic.

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