MORPHOLOGICAL ANALYSIS AND PALAEOECOLOGY OF THE SEED FERNS OF THE GENUS ODONTOPTERIS (BRONGNIART) STERNBERG FROM THE LATE PENNSYLVANIAN OF THE DONETS BASIN

Abstract

The morphological features of foliage and palaeoecology of the Late Pennsylvanian odontopterid seed ferns from the Donets Basin are considered. The fossils indicate that the young fronds of Odontopteris schlotheimii had a dichotomous rachis at an angle of 70° and large oblong pinnules above a dichotomy with the well-pronounced thick midvein and lateral veins that emitted from the midvein along its entire length. The ontogenetic variations of the ultimate pinnae of Odontopteris schlotheimii are manifested in the increasing segmentation of a leaf blade and the change of pinnule sizes and pinnule density on the axes with different thickness. The ontogenetic variations of the ultimate pinnae of Odontopteris subcrenulata and O. cantabrica are expressed by the change of pinnule sizes when changing the axis thickness. The typical pinnules without ontogenetic changes are described on a few small specimens of Odontopteris brardii and O. lingulata that are presented by the ultimate pinnae.On the basis of the lithological and facial features of plant-bearing deposits, the interpretations of the landscape conditions of odontopterid distributions are carried out. The pteridosperms Odontopteris cantabrica were common in wet swampy lowlands along with ferns in Kasimovian and early Gzhelian times. Odontopteris brardii grew within deltaic plains with a moderately wet and drained substrate in early-middle Gzhelian time. The pteridosperms Odontopteris lingulata were distributed on floodplains in middle Gzhelian time. The pteridosperms Odontopteris subcrenulata were spread on floodplains and the slopes of river valleys with seasonally dry conditions in Kasimovian and early-middle Gzhelian times as well as on coastal lowlands in the conditions of progressive climate aridization in late Gzhelian time. Odontopteris schlotheimii grew on deltaic plains and floodplains in early-middle Gzhelian time as well as on moderately wet coastal lowlands and on lagoonal plains with seasonally dry conditions in late Gzhelian time.