Bundenbach Orbiculoidea mediorhenana
8.5 cm (fossil), 19×24 cm (matrix)
Bundenbach; Obereschenbach pit
Very large and rare brachiopod on unbroken slab with excellent details.
Orbiculoidea mediorhenana – The golden discus of the Hunsrück slate
A rare, inarticulate brachiopod.
In the world of fossils, it is often the simple forms that exert the greatest fascination. Orbiculoidea mediorhenana is the best example of this. While other arthropods relied on ribbed, heavy shells, this exotic chose a design that could still be considered modern today: a perfectly circular, flat-conical shell that looks like a sunken shield in the black slate.
The distinctive features – what makes Orbiculoidea so special:
- The perfect circular shape: the name says it all (lat. orbiculus for small circle). The bowl is almost exactly circular and has a very fine, concentric growth striation. In the play of light in the display case, this structure is reminiscent of the grooves on an antique record or a fine piece of jewelry.
- Inarticulate elegance: In contrast to most brachiopods, Orbiculoidea does not have a mechanical lock (inarticulate). The shell halves were held together purely muscularly. This gives the fossil a smooth, undisturbed contour, which is considered particularly aesthetic in paleontology.
- The “apex”: The shell is slightly curved in a cone shape, with the apex often being slightly off-center. This gives the fossil an exciting spatial dynamic.
- Pyritization in perfection: As the shells of Orbiculoidea originally consisted of an organic-phosphatic substance, they were often pyritized particularly brilliantly in the Hunsrück slate. A well-preserved piece shines like a flat taler of real gold on the dark rock.
A survivor of the earth’s history from Bundenbach
The genus Orbiculoidea is a fascinating example of evolutionary consistency. This construction plan was so successful that it remained almost unchanged for hundreds of millions of years. A specimen from the Rhenish Devonian such as O. mediorhenana documents this success in a level of detail that is unparalleled worldwide.
