A new Mesozoic Ginkgo from western Liaoning, China and its evolutionary significance

Abstract

Well-preserved Ginkgo ovulate organs and associated leaves are described from the fossil-bearing Yixian Formation of the Late Jurassic or Early Cretaceous in Liaoning Province, China. The ovulate organs bear a cluster of (up to 6) ovules at the apex of peduncle. The ovules are seated each in a cup-shaped collar, terminating a short pedicel in the small juvenile organ, but attached directly to the peduncle with maturation. There are one to three seeds on the mature ovulate organ, which are roughly circular in outline. Associated leaves are small, with flabellate and dichotomously divided lamina. The new Ginkgo is morphologically intermediate between the Jurassic Ginkgo yimaensis and the extant Ginkgo biloba, but much closer to the latter and essentially of the modern type in ovulate organs. It fills up the wide gap between the Middle Jurassic and Palaeocene in the fossil record of Ginkgo ovulate organs. The finding provides new evidence supporting the reduction hypothesis for Ginkgo evolution. It is likely that the drastic climatic changes during the Late Jurassic and Early Cretaceous were responsible for the transformation of the ovulate organs of the Jurassic G. yimaensis type into the modern G. biloba type.