Huge Cryptozoan rosemontensis Ordovician Stromatolites

Coming from the Lower Ordovician Oneota Formation, it is some 495 million years old, from a time that Prokaryotic life forms no longer had exclusive use of earth's shorelines. Concomitantly, the earth's coastal habitats had markedly reduced stromatolite reafs, compared with the Proterozoic.

By this time in geological history, microbial communities consisted of complex consortia of both prokaryotic and eukaryotic forms with diverse metabolic needs, and competition for resources and differing motility among them made for an intriguing microcosm of interacting life, some autotrophic, some chemotrophic and some heterotrophic.

This particular specimen has been cut horizontally through a vertical column to reveal complex wavy laminae. This is a huge specimen measures more than 13 inches across the wide dimension. Cutting such a slab requires a very large saw blade.

Interestingly, the top edge is along a shear plane cut by a glacier in the last ice age.