Lakes Neuropteris Fossil with Exceptional Preservation
Time: Pennsylvanian (~300 m.y.a.)
mm = 1 inch): Plant fossil is 51 mm long by 15 mm across on a 35 mm by
53 mm nodule
Dresden Lakes, Francis Creek Shale, Grundy County, Illinois
The Mazon Creek deposits of the region near Braidwood, Illinois rival
the other famous Lagerstatten of the Burgess Shale, Solnhofen, and
Liaoning for the variety of detailed life preserved. Many exquisitely-preserved
specimens are found in the ironstone nodules that make up the deposits.
The majority of collecting areas are the spoil heaps of abandoned
coal mines. This particular nodule, however, comes from Dresden Lakes
in Grundy County Illinois. Like the better-known Pit 11 site near
Braidwood, Illinois, this location became the site for cooling ponds
for a nuclear power plant. The site is well known for the dark coloration
that while esthetically pleasing is somewhat harder to photograph.
I recently had an opportunity to acquire a collection that was made
in the 1950’s. Pteridosperms or seed ferns are a group of extinct
plants with mostly fern-like foliage but with real seeds. They are
mostly reconstructed as small trees but also forms with a climbing
growth habit gave been found. Some forms, notably those called the
Medullosales, have large fronds which could be up several meters long.
Several groups can be distinguished within the Pteridosperms. The
Pteridosperms evolved in the latest Devonian, and became common in
the Carboniferous. The Medullosales took over the leading role during
the Westphalian and persisted into the Permian. This one is a pinnule
of Neuropteris. Note the shiny look to the specimen which is the result
of a carbonized film remnant of the original plant tissue.