Reconstruction and architecture of medullosan pteridosperms (Pennsylvanian)

A new reconstruction of the architecture of medullosan pteridosperms is proposed on the basis of three stems preserved as compression-impression fossils: one from the Southern Anthracite Coal Field of Pennsylvania (lower part of Llewellyn Formation, Pennsylvania, Westphalian D) probably belonging to Alethopteris foliage; a second stem from the roof shale of the Eagle coal bed (Kanawha Formation, Middle Pennsylvanian, Westphalian B) of West Virginia, associated with Neuropteris foliage; and a third reported from the Stephanian of Commentry, France, in connection with Odontopteris foliage. The diameters of the Llewellyn, Eagle, and Commentry stems are 17 cm, 13 cm, and 6.5 cm, respectively. All three stems bear remnants of petioles up to several centimeters in length. The petolar remnants indicate that the living leaves grew upward at an angle of 30 - 60 degrees from the vertical, a growth habit that is common in present day tropical plants with similar overall architecture. Leaves drooped only when they were dying. After decay they broke off and left short petiolar remnants bent downward. The Llewellyn and Eagle stems represent plants with thick, straight stems, whereas the Commentry specimen shows a thin and slightly curved stem