PALEOLATITUDINAL GRADIENTS IN SEED SIZE DURING THE CRETACEOUS-TERTIARY RADIATION OF ANGIOSPERMS

An updated data set of 25 fossil floras sampling plant communities from the Early Cretaceous (similar to 123 million years ago) to the Pliocene (similar to 3 million years ago) is reanalyzed to assess the evolution of a latitudinal gradient in seed size during the radiation of angiosperms and the effect of this gradient on estimations of temporal trends in seed size. There is a significant negative correlation between the median seed size of Tertiary floras and their paleolatitude. As in modern floras, average seed size decreased from the equator toward the poles. Results indicate that previous documentations of a striking increase in within-flora seed size around the Cretaceous/Tertiary boundary (66 million years ago) are valid and conservative: the older (Cretaceous) floras sampled communities that in life were closer to the equator, relative to the younger (Tertiary) floras.