As some of you may know, Dave Douglass, the original founder of Dave's Rock Shop, has one of the most complete collections of Mazon Creek material in the world. Although most of that collection is housed in our private museum, we have decided to begin offering other Mazon Creek material in our shop and here online. We're beginning with Tully Monsters and we'll gradually increase the available specimens. So, check in every now and then!

The Mazon Creek Biota of Illinois represents the most complete record known of a late Paleozoic community of animals and plants. As a Konservat-Lagerstätte (a deposit with exceptional fossil preservation), this extraordinary fossil assemblage ranks among other great fossil sites of the world, such as the Precambrian Ediacara of Australia, the Cambrian Burgess Shale of Canada, the Devonian Bundenbach and the Jurassic Solnhofen of Germany. Occurring in the 307 million-year-old Middle Pennsylvanian Francis Creek Shale, the Mazon Creek Biota comprises one of the most diverse fossil floras in North America - roughly 123 biological species - and also encompasses more than 500 animal species constituting 11 phyla and 23 classes. Many soft-bodied groups are represented among the fossil fauna specimens, as well as insects and complete vertebrate skeletons with soft parts. All were rapidly buried during a major flooding event. The stage was set by global warming and a change in tropical climate from consistently wet (with widespread equatorial coal swamps) to monsoonal. The latter alternating wet and dry seasons repressed plant growth and spawned intense upland erosion and delta progradation. Terrestrial, freshwater, estuarine, and a few marine organisms succumbed to the accumulation of river-borne silt and clays, and were then beautifully preserved in siderite (iron carbonate) concretions. Rising sea level caused by melting of the south polar icecap and compacting delta sediments assured their preservation in the geologic record. The site, located near Chicago, is accessible to hundreds of amateur collectors who are responsible for most of the rare animals and plants of the Mazon Creek area that are exhibited in museum collections.