ALETHOPTERID OR NEUROPTERID? DISTINGUISHING MYELOXYLON IN COAL BALLS

In the Pennsylvanian, adpressed pinnules (leaves) record the presence of medullosan seed ferns on flood plains, while permineralized stems, roots and fronds record their presence in peat swamps. In flood-plain sediments, Alethopteris and neuropterid pinnules are the most common medullosan seed-fern fossils. These pinnules also occur in coal balls, however the petioles and rachides of medullosan compound leaves, known as Myeloxylon, are more common. In Duquesne Coal, Pryor (1990) established criteria for the identification of Myeloxylon associated with alethopterid or neuropterid pinnules. Here, we apply and extend the criteria created by Pryor to Mid-Miscovian Myeloxylon from three Iowa mines. Features used to separate alethopterid from neuropterid Myeloxylon in Dusquesne coal balls that also apply to Myeloxylon from the Williamson No. 3 Mine (Lucas Co., Iowa) include: 1, the shape of the sclerenchyma strands in the hypoderm; 2, the shape of sclerenchyma strands as medullosan compound leaves separate from the stem, and 3, presence or absence of a palisade epidermis, although this is rarely preserved. Sclerenchyma strands that curve around resin ducts is a new character that may help to identify alethopterid Myeloxylon in both deposits. Neuropterid sclerenchyma strands are square or round in cross-section and do not curve around resin ducts. Approximately 9 million years separate the younger Duquesne Coal in the mid-Ghzelian from the older Williamson No. 3 deposit in the mid-Moscovian. The Duquesne Coal is one of the youngest coal-ball localities in North America and the Williamson No. 3 Mine is among the oldest. If the criteria used to separate alethopterid from neuropterid Myeloxylon in the Duquesne Coal can also be applied to Myeloxylon in Williamson No. 3 coal balls, we should be able to use these criteria to identify alethopterid and neuropterid Myeloxylon in most North American coal ball deposits.