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Dinosaur/cycad coevolution



Last month several people inquired about the availability of reprints of my paper "Coevolution of cycads and dinosaurs" that appeared in Cycad Newsletter vol.. 30, no 1, 2007, p. 6-9. The Introduction appears below. I'll be happy to provide reprints either as a PDF file or as a hardcopy. Just email me at mustoeg@cc.wwu.edu. My interpretation of the paleobiology of cycads and herbivores is a bit off paleontology's beaten path, and I welcome comments and criticisms.
George Mustoe
Geology Department, Western Washington University


INTRODUCTION

Cycads were a major component of forests during the Mesozoic Era, the shade of their fronds falling upon the scaly backs of multitudes of dinosaurs that roamed the land. Paleontologists have long postulated that cycad foliage provided an important food source for reptilian herbivores, but the extinction of dinosaurs and the contemporaneous precipitous decline in cycad populations at the close of the Cretaceous have generally been assumed to have resulted from different causes. Ecologic effects triggered by a cosmic impact are a widely-accepted explanation for dinosaur extinction; cycads are presumed to have suffered because of their inability to compete with fast-growing flowering plants that appeared during the mid-Cretaceous “angiosperm explosion”. This paper explores a different hypothesis, i.e., that the evolutionary fates of cycads and dinosaurs were inextricably intertwined, and the Late Cretaceous extinction of these reptiles was the triggering event that caused cycads to diminish to their present status as “living fossils”. The main tenet of this hypothesis is cycads depended on herbivorous dinosaurs to disperse their seeds, and the disappearance of these herbivores led to a precipitous decline in the geographic range and numerical abundance of cycads. Evidence comes from the toxicology of extant cycads, their seed dispersal strategies, anatomical characteristics of herbivorous dinosaurs, and the geographic distribution and taxonomic diversity of modern and fossil cycads.