Stigmaria
is a form genus for tree roots of Carboniferous coal forest Lycopod
trees such as Sigillaria and Lepidodendron. Lycopodiophyta appear
in the fossil record
in the Silurian in conjunction with many other vascular plants,
and led to the trees
that would dominate the equitorial landscape in the Mississipian
and Pennsylvanian periods. North America was at the equator during
the Carboniferous (290 to 359 million years ago). There were extensive,
hot and swampy forests with Pteridospermatophyta (seed ferns) and
huge Lycopodiophyta trees, Sigillaria and Lepidodendron, some on
the order of 30 meters tall with trunks
a
meter or more thick. West Virginia during the Carboniferous period
was a vast coastal swamp extending for hundreds
of miles
that was
barely
above
sea level.
Unlike
modern trees, lycopid tree leaves grew along the full extent
of the trunk and branches, falling off
as the plant grew, leaving but a small cluster of leaves
at the top. These forests became the coal seams we mine for fuel
in
moderm times; stigmaria are often impregnated with coal,
or
have coal
sticking to their surface. Note the round nodes on the surface
of this fossil, which is where small roots grew out in all
radial directions. Good fossil specimens are essentially found
in coal
seams per se, since the details would have been destroyed
during coalification. However, in the interburden layers between
coal
seams, fossils like this one are found, though rarely. This
one underwent partial coalification on its outer surface. |