Cretaceous Angiosperms: Evolutionary, Geographical and Palaeoclimatic Aspects (On the S. V. Meyen’s Scientific Legacy)

The additional arguments regarding Cretaceous evolution of angiosperms are provided which further develop the evolutionary ideas of S.V. Meyen. The quantity, diversity and geographical distribution of angiosperms, which first appeared at the beginning of the Cretaceous (in Berriasian), had been increasing significantly starting from the end of the Albian. This could be due to the fact that for the first time in the Cretaceous history of the Earth, a hot and humid equatorial belt appeared in the Albian and acted as a “generator of suprageneric taxa” of higher plants. The speed of the angiosperm macroevolution had increased dramatically due to the development of this belt, while the fluctuations in the Late Cretaceous climate “launched the equatorial pump at full capacity.” The anatomy of the Triassic bennettitalean microsporangium Leguminanthus indicates that this group of gymnosperms possessed a morphological structure, which could have led to the formation of a closed (with closed margins) seed organ similar to the carpel of angiosperms, probably by means of a large evolutionarily significant saltation – gamoheterotopic transformation of female bennettite fruitifications to the anatomy of male ones. The presence of wide and probably flattened petioles and rachis in the Triassic bennettitalean Pterophyllum leaves confirms indirectly the validity of the assumption that angiosperm leaves could have evolved from those of bennettitaleans by means of phyllodization (flattening and enlargement of the leaf petiole).