Compressions of Sequoia (Cupressaceae sensu lato) from the Middle Jurassic of Daohugou, Ningcheng, Inner Mongolia, China

Abstract

The specimens (two pairs of part and counterpart) of coniferalean branched leafy shoots were collected from the Jiulongshan Formation (Middle Jurassic) at the village of Daohugou, Ningcheng, Inner Mongolia, China. The fossil material displays helical phyllotaxy, dorsiventrally flattened linear, sessile leaves with decurrent base and prominent and single mid-vein. The foliate shoots are assigned to Sequoia jeholensis by comparing those of the genera Yanliaoa, Sequoia, Metasequoia, Taxodium, and Glyptostrobus, the basal members of the Cupressaceae sensu lato. Sequoia jeholensis is the oldest Sequoia species to date. It has coriaceous, dimorphic, helically arranged linear and scale leaves, with entire margins, attached obliquely to the axis by their decurrent bases. The leaf cuticle of S. jeholensis is described here for the first time. Leaves are hypostomatic, with stomata only on the abaxial surface. Anticlinal walls are straight, with single or more often paired pits. The epidermal structures of Sequoia are one of the key characters to distinguish it from similar genera, but they usually could not be used to distinguish the species within Sequoia. The Middle Jurassic of Daohugou represents a lacustrine environment with a warm and humid climate reflected by the species assemblage. So, the extinct Sequoia probably had similar climatic requirements to those of extant Sequoia sempervirens.