The genus Trochodendroides Berry in the cretaceous floras of Siberia

Abstract

Seventeen species of the genus Trochodendroides and one species of the genus Nyssidium are described from the Albian-Maastrichtian deposits of the Chulym-Yenisei depression (Western Siberia), Lena-Vilyui depression (Eastern Siberia) and Kolyma River basin. The study of recently collected materials and revision of previous data allow us to describe 4 new species (T. buorensis Golovn., sp. nov, T. beketovii Golovn., sp. nov., T. rostrata Golovn. et P. Alekseev, sp. nov.) and to offer 6 new combinations (T. tiungensis (Budants.) Golovn., comb. nov., T. heterophylla (Budants.) Golovn., comb. nov., T. kemensis (Ananjev) Golovn., comb. nov., T. sibirica (Tcherepnin) P. Alekseev, comb. nov., T. bajkovskae (I. Lebed.) Golovn., comb. nov., T. gromovii (E. Lebed.) Golovn., comb. nov). The new names were proposed for two species (T. budantsevii Golovn., nom. nov., T. ananjevii Golovn., nom. nov.). The morphological diversity, variability and value of different characters for distinction of species are discussed. The epidermal features were firstly examined for T. heterophylla and T. ananjevii. They are mostly similar to epidermal features of Cercidiphyllum. The genus Trochendroides firstly appeared in Siberia in the early-middle Albian as a minor component of the conifer-dominated Mesophytic floras. The determination of this genus is verified by the findings of Nyssidium fruits. During the Late Cretaceous the genus Trochodendroides was common member in floras of the Siberian-Canadian phythogeographic region. The systematic and morphology diversity of Trochodendroides was comparatively low in the late Albian–Cenomanian and the findings of these leaves are rare. The abundance of Trochodendroides leaves was increased in the Turonian and the Coniacian. During the Coniacian this genus reached the highest systematic and morphologic diversity (the Antibes and the Vilyui floras). In the Santonian-Campanian the abundance of Trochodendroides leaves was decreasing again. In this time the lanceolate or narrow-ovate leaf morphotypes were most usual. They were often described as Macclintockia, Zizyphus or Paliurus. Genus Trochodendroides is not presented in the Cretaceous deposits of Europe and firstly appeared there in the Tertiary. This genus is rare in the Late Cretaceous deposits of the Turan province, near the boundary between Siberian-Canadian and Euro-Sinian phythogeographic regions.