Mazon Creek Pecopteris Fern Fossil
Time: Pennsylvanian (~300 m.y.a.)
fossil is 118 mm long by 18 mm across (maximum); Nodule: 130 mm by 62
mm nodule half
Mazon Creek, Francis Creek shale, Morris, Illinois
The Mazon Creek deposits of the region near Braidwood, Illinois rival
the other famous Lagerstatte 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 Mazon Creek
itself, and was collected directly from the stream bed many years
ago. Most genera and species of plants were originally described from
this region, so this specimen can be considered a topotype. The Pteridophyte
(tree fern) Psaronius became a dominant form supplanting the lycopods.
The leaf fronds and pinnules of Psaronius were given the form genus
designation of Pecopteris, a highly variable form whose classification
is still under review. This is a fine large example which fills is
enclosing half nodule.