This is Mazon Monday post #25. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
-----------------------------------------------------
The species spotlight falls on Mazonomya mazonensis, known mistakenly as Edmondia for a long time. It was also called affectionately clam-clam.
Preserved in the "death position" from Chowder Flatts.
Here is the text from the Mazon Creek Fossil Fauna by Jack Wittry.
Mazonomya mazonensis Bailey, 2011
Found in numbers that exceed the combined total of all other clams, Mazonomya mazonensis, commonly called Clam-Clam, is ubiquitous in the Mazon Creek Biota. Concretions containing numerous individuals are frequently found in collections. This species is equivalved. with rather smooth shells lacking valve ornamentati1on except for growth lines. It has an elliptical out line and a valve width that is about one-half of the average 30 mm length. It is usually found in the death position: both valves opened. butterfly-like. The flexible hinge ligament is often preserved and seen stretched between the valves. (See Figure 105.2 and 105.4 below.) As they moved through the substrate, M. mazonensis produced many of the fossil trails that appear in concretions. (See Trails, page 157.)
Misidentified as an Edmondia years ago, recent studies show that this species is a solemyid, a group today found living in the mud of oxygen-poor and sulfide-rich waters, such as present-day salt marshes.
Here is the text from Creature Corner.
The Bivalve Edmondia
Early researchers of the Mazon Creek Biota considered the fauna discovered in the nodules of that strata to be transients, non-resident creatures which had been trapped by some storm or other natural disturbance, carried out to the delta front and buried. Sealed in an iron concretion, siderite to be exact. The finding of bivalvia in nodules crippled that idea. Here we had creatures that burrowed .* into the mud or limey silt; a bottom dwelling resident of the delta front. As a class, bivalvia are tolerant of slight changes in salinity, water temperature, and water quality. A creature able to adapt to slight changes or at least tolerant of conditions around the delta front. Concretions holding bivalves sometimes had indications of the clam trying to burrow out and up (?) from its enclosing media. What sort of mechanism or condition could seal a bivalve in its burrow? Encase it in an iron carbonate nodule?
The members of the genus Edmondia found in the Mazon Creek area are under study at the present time. At this date it is felt that all belong to one species. It is one of the more abundant bivalves in the northern part of Pit 11, Morris and Ottawa. In life it is believed to have been a shallow burrower. Edmondia are egg-shaped or nearly so, from a side view. Edmondia are equivalved, with a nearly smooth surface. Some specimens are found in life position with valves closed, others with valves open, denoting burial after death.
From Chowder Flatts
From Braceville
