The rise of ginkgoalean plants in the early Mesozoic: a data analysis

AbstractIn the present article, ginkgoalean fossil records are analysed and the data are incorporated into a sketched, ‘epoch‐by‐epoch’ framework (e.g. late Triassic, early Jurassic), based on the latest biostratigraphical evidence and the recent progress made mainly on the reproductive organs. The analyses revealed that a steep increase in diversity occurred from the middle Triassic onwards and during the late Triassic ginkgoaleans were at the zenith of diversity. In the late Triassic, almost all known ginkgoalean families simultaneously occurred. The diversity of vegetative organs increased rapidly, forming a high peak in the number of genera (8 in China and 12 in the world). In the late Triassic, in marked contrast to the absence of any record in the middle Triassic, there occurred the most diversified ginkgoalean reproductive structures so far known in the geological record. The emergence of a large number of new genera also supports an early Mesozoic, notably a late Triassic radiation of ginkgoaleans. In China, Ginkgo was recorded firstly in the late Triassic, and the commonest morphogenera Ginkgoites, Baiera and Sphenobaiera drastically increased in specific (or morphotypic) diversity from the late Triassic onwards accompanied by very high origination rates of 88.8, 100 and 91.7%, respectively. The major morphological innovations of vegetative organs accomplished in the middle to late Triassic are the appearance of dwarf shoots and the differentiation of leaves into lamina and petiole. Since then, the reduction of pedicels and number of ovules, and the increase in size of ovules became dominant. Further morphological innovations and diversification of ginkgoalean ovule organs include the fused or adnate ovule/bract, and the collared or winged ovules. In China, ginkgoaleans also started expanding rapidly in geographical distribution from the middle Triassic to the late Triassic. The fossil localities of Ginkgo increased from zero to three, Ginkgoites from one to 12, Baiera zero to 27 and Sphenobaiera three to 20 counties.The replacement of the warm‐hot, nearly uniform climate with long growing season in the late Palaeozoic by the seasonal climate in the early Mesozoic of Eurasia was probably the main cause of a marked reduction of both vegetative and reproductive organs of ginkgoaleans. The latest Triassic plate movement and sea‐level change that resulted in considerable habitat heterogeneity might also facilitate an increase in taxon and morphology diversity of this present‐day relictual plant group. Copyright © 2006 John Wiley & Sons, Ltd.