The floristic relationship between the upland and lowland Carboniferous wetlands of Variscan Euramerica — Evidence from some medullosalean pteridosperm fronds

摘要

Alethopteris grandini represents remains of fronds of a medullosalean pteridosperm (probably a small tree) that rapidly migrated across the lowland wetland habitats of Variscan Euramerica in middle Asturian (late Moscovian) times. This was probably caused by changing drainage patterns within the lowland coal swamps, in response to climate and landscape changes. However, these medullosaleans had first appeared rather earlier, in early Bolsovian (early Moscovian) times, in upland wetland habitats. These upland habitats may have pre-adapted these plants to the changed condition in the lowland coal swamps.