New material of Coniopteris simplex from the Middle Jurassic of the Ordos Basin, Inner Mongolia, China and implications on its spatio-temporal distribution and paleogeography

Abstract

Coniopteris simplex is a common component in many Jurassic floras. However, due to morphological variations in sterile fronds and incomplete preservation of reproductive organs, its classification has been controversial for a long time. Here, we present new material collected from the Middle Jurassic Yan'an Formation in the Ordos Basin, Inner Mongolia. The new material reveals important morphological characters, including hemi-dimorphic fronds, two forms of sterile pinnae, short-stalked sori and sporangia on fertile fronds, annulus of sporangium composed of about 30 cells, in situ rounded triangular spores with protruded suture, and the lips of trilete laesura encircled by one or two rows of small ostioles. Based on these observations, we emended the diagnosis of this common species. The spatio-temporal distribution of Coniopteris simplex shows that the iconic species was restricted to the paleolatitudes ranging from 19.5°N to 48.9°N in the Northern Hemisphere during the Early–Late Jurassic, mainly distributed in the tropical to paratropical zones, and the paleolongitude ranging from 9.6°E to 129.3°E, which may be limited by the opening of the Viking Corridor and the splitting of the Central Atlantic Ocean.