Fossil evidence of initial radiation of Cercidiphyllaceae

Abstract

Cercidiphyllaceae-like leaves and fruits from the Lower Cretaceous deposits of Northeastern Asia were restudied. In the result one species of Jenkinsella fruits and five species of Trochodendroides leaves were recognized, including Trochodendroides potomacensis (Ward) Bell, T. buorensis Golovneva, T. sittensis Golovneva, sp. nov., T. vachrameeviana (Iljinskaja) Golovneva, comb. nov., and T. denticulata (Budantsev et Kiritchkova) Golovneva, comb. nov. Two new combinations and one new species are published. These plants had very small leaves and probably were shrubs. Fruits of Nyssidium orientale Samylina from the Barremian-Aptian Starosuchan Formation (Primorye, Russia) have no follicular characters as Jenkinsella fruits. Their affinity, not only to Cercidiphyllum-like plants, but to angiosperms in general, is doubtful. Leaves and fruits of Cercidiphyllum sujfunense Krassilov from the lower-middle Albian Galenki Formation (Primorye) also can not be assigned to Cercidiphyllaceae. Leaves have pinnate, brochidodromous venation and are comparable with those of Asiatifolium elegans Sun, Guo et Zheng, which were recorded from the Frentsevka Formation of the Partizansk coal basin, Primorye, Russia, and from the Chengzihe Formation, Northeastern China. Thus, the first reliable records of the genus Trochodendroides appear in the early-middle Albian. The relationship of these leaves with Cercidiphyllaceae is confirmed by finds of associated fruits Jenkinsella filatovii and by significant diversity of Trochendroides in the Late Albian-Cenomanian. In the early-middle Albian the genus Trochendroides was a minor component of the conifer-dominated Mesophytic floras. These fossils reflect the early radiation of Cercidiphyllaceae and indicate that this family began to diversify more then 30 million years before the Tertiary. Investigation of the early-middle Albian Cercidiphyllaceae provides important new data for our understanding of the early evolution of eudicots.