Loriolaster mirabilis (Ophiuroid or brittlestar fossil)
Geological Time: Lower Devonian, Seigenian - Emsian Stage
Size: 52 mm armspan on a 193 by 130 mm matrix
Fossil Site: Hunsruck Slate, Bundenbach Germany
 Description:
Well-preserved example of an Ophiuroid ( brittlestar) known as Loriolaster
marabilis. The Hunsruck slate is famous for its fossils, many of which
have pyritization present. Rapid burial and pyritization was what
led to the many wonderful examples of early Devonian life from the
region. The chemistry of the silt was such that low organic content
and high levels of iron and sulfur allowed the pyrite to diffuse into
the tissues rather than be deposited in the sediment. The  mudstones
were metamorphosed into slate during the Carboniferous. The slate
was quarried for roofing tiles, and the quarrymen would save the fossils
for later sale. Now that the quarries are no longer open, future supplies
of these wonderfully-preserved benthic organisms will only come from
existing collections. This one displays excellent preservation, including
the “skin” which stretched between the arms. The Bundenbach
region preserves the most diverse mid-Paleozoic starfish fauna known
in the world. Roughly 1/3 of them show some degree of tissue preservation.
The genus derives its name from the net-like membrane seen stretched
between the arms. The web-like skin seen here is quite spectacular.
To what purpose could it have been used? One thought is that it provided
a means of keep the starfish at the surface of a soft sea floor; I
would think that the arms would have done that job quite well. To
me, a more likely scenario is that thy may have used it as a net much
like the modern-day bat star Asterina which preys upon other starfish
as well as other items. Some even think they filter feed. Whatever
the true purpose, this is a most exceptional example, one offered
here at a most reasonable price. |
