Acanthodes
sp
Infraphylum
Gnathostomata, Class Acanthodii, Order Acanthodiformes
Geological
Time: Pennsylvanian (~300 m.y.a.)
Size (25.4
mm = 1 inch): Fossil is 40 mm long;
Matrix: 30 mm by 50 mm and 47 mm by 24 mm nodule pair
Fossil Site:
Pit 11, Francis Creek Shale, Braidwood, Illinois
Code: HMC13
Price: $1595.00
- sold
 Description:
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, the most famous of which
is  Peabody Coal Pit 11. Pit 11 now serves as a cooling pond for
the Braidwood nuclear power plant, but with over 100 other localities,
specimens still come to light. This one is of the fossil fish
Acanthodes, preserved here in lateral aspect. Note the pigmented
retinas, spines in the fins, and the tail fin. The Acanthodians
are jaw-bearing fish who still are the subject of dispute over
their systematic position. They possess highly-advanced, spindle-shaped
bodies thought to have made them swift swimmers. The body was
covered in small mosaic-like scales. They possessed small teeth
which were typically confined to the lower jaw; some were toothless.
The feature they all share in common is the fact that all fins
other than the caudal are supported by massive spines formed
of dentine. Indeed, the name Acanthodii is derived from the Greek
word for spine. The oldest acanthodian lived during the late
Ordovician. They reached their peak during the Devonian, and
became extinct during the Great Dying of the end-Permian extinction.
This is beyond a doubt the finest example I have ever come across.
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