You are bidding on a Mazon Creek Fish Fossil
Class: OSTEICHTHYES (bony fish)
Order: Crossopterygii (coelacanths, lobe-finned fishes)
Family: Rhabdodermatidae
Genus: Rhabdoderma
Species: exiguum (Eastman)
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 exquisite example is one of the Coelacanth fish, a primitive lobe-finned fish which underwent a dramatic radiation during the Carboniferous.This is an extremely well-preserved lateral view of a Pennsylvanian Period (325-280 mya) "Rhabdoderma exiguum", it shows the fins, eye, gills, rays, even the lateral line are clearly visible. Forey and Lund and Lund (1985) consider Rhabdoderma to be a primitive coelcanth showing broad, partly, overlapping cheek bone forming a complete cover behind the eye. The premaxilla carries a few large teeth, while other tooth-bearing bones show fine granular teeth. The pelvic fin originates behind the first dorsal fin. The air bladder, where it is known, shows calcified walls, a rather easily seen character in the Mazon Creek biota specimens. The scales show a pattern of elongate ridges and tubercles, which converge posteriorly toward the midline of the scale. Specimens of juvenile individuals, like this one, show a circular expansion below the abdomen, which represents the yolk sac. This species of fish was ovoviviparous, meaning that eggs were fertilized internally and are retained in the mother's oviduct so that the young are born alive. The growing young live off a large yolk sac until birth. Such small coelacanth fossils also possess a much elongated, central caudal lobe.
Rhabdoderma exiguum is an inadequately described species based on small specimes. Specimens are recognizable by the two dorsal fins, elongate supplementary (mid caudal lobe), and the lobed paired fins. This specimen is one of the best preserved Mazon Creek fish I have ever seen. This along with the exclusivity of the fossil make it a must-have for the serious fish fossil collector.Fish are found in 0.13% or 1.3 out of every 1000 fossils discovered in Mazon Creek pits.
The dimensions of the fossil are: 7.5 cm x 6 cm x 2 cm. E-mail me with any questions or special requests.
C.W. Shabica and A.A. Hay (editors), 1997, The Fossil Fauna of Mazon Creek, Chicago: Northeastern Illinois University, 308pp.
Current Price: $ 1237.0
