In an important paper, Wnuk and Pfefferkorn (1984) described parautochthonous assemblages of medullosan pteridosperms from Pennsylvania, USA.
More than 95% of this plant material comprises remains of medullosan pteridosperms, including trunks [less than or equal to] 95 mm in diameter that show resin rodlets and downward-recurved petioles, large bifurcating petioles [less than or equal to] 56 mm in diameter, and pinnae of Macroneuropteris scheuchzeri with cyclopterid pinnules, and Neuropteris ovata.
The presence of a fossil flora consisting of sphenopsids, lycopsids, cordaitaleans, a varied suite of ferns (including tree fragments), and more occasional pteridosperms
, is indicative of a humid environment.
Drifted lycopsid plants predominate in the basal limestones, whereas overlying siltstones and sandstones contain a mixed suite of drifted gymnosperms (cordaitaleans), sphenopsids (primarily calamiteans), pteridosperms
and putative progymnosperms (Falcon-Lang 2003a).
From this Psilophyton-like type were derived two lines of evolution--the lycopods, on the one hand, which retained their phylloids and dichotomous cauloids, and, on the other, all other vascular cryptogams, the pteridosperms
, all gymnosperms and angiosperms.
and cordaitaleans were assisted through dry periods by a substantial root system, which allowed them to tap deep groundwater sources (Falcon-Lang and Bashforth 2004).
DiMichele and Phillips (1977) described the monocyclic Psaronius simplicicaulis from an Early Pennsylvanian bedrock valley-fill succession in Illinois (Leary 1981), where it was associated with an upland/dryland assemblage of cordaitaleans, pteridosperms
, and noeggerathialians (Leary 1975, 1993).
and shade leaves in two Jurassic species of pteridosperms
1990) raised the important question about cauline-borne ovules for pteridosperms
some Paleozoic pteridosperms
and is established as a character in
Seasonal dryland environments were apparently colonised by ecologically stressed, fire-prone vegetation dominated by cordaitaleans and medullosan pteridosperms
(Falcon-Lang 2003a, 2003b), and additionally supported a low-diversity fauna of invertebrates and tetrapods (Hebert and Calder 2004; Falcon-Lang et al.
form a heterogeneous group of gymnospermous plants with fernlike foliage and were widely distributed during the late Paleozoic.
Literature on medullosalean pteridosperms
, in contrast with other studied groups of Carboniferous plants, is very large and reflects a most intensively investigated Palaeozoic plant group.
Several fossil and extant cycad leaves show an external morphology similar to that of Bennettitales and Pteridosperms
This assemblage represents fire in lowland peat-forming communities dominated by Sigillaria and medullosan pteridosperms