World Congress of Malacology Antwerp ... - Unitas Malacologica

danasteri. Theodoxus velox is distinct from the so-called “T. fluviatilis complex”, which comprises
four well-supported clades. Using an average COI molecular clock rate for Protostomia of
2.23±0.22% K2P distance/My, we estimate the age of the split of T. velox from its sister clade at
1.37±0.29 My. At this time during the early Pleistocene a relatively small and isolated brackish water
body - the Gurian Sea - existed in the Euxinian depression. Freshening, cooling and decrease of water
level during that time could have had a vicariance effect on the common ancestor of T. velox and the
T. fluviatilis complex. According to our data, T. cf. danasteri, previously referred to as “Danubian T.
fluviatilis group” forms a sister clade to the group containing W European T. fluviatilis and T.
euxinus. The significant differences among T. velox, T. euxinus and T. cf. danasteri could be
confirmed utilizing morphometrical analysis of shell geometry.
The evolution of Black Sea Basin Theodoxus lineages in time and space is discussed in a Pan-
European context.
Exceptional preservation of molluscs in the buckhorn asphalt quarry
Seuß, B. 1 ; Nützel, A. 2 ; Schulbert, C. 1
1. Institut für Paläontologie, Universität Erlangen-Nürnberg, Loewenichstraße 28, D-91054 Erlangen,
Duitsland,
Email: barbara@pal.uni-erlangen.de; chris@pal.uni-erlangen.de
2. Bayerische Staatssammlung für Paläontologie und Geologie, Richard Wagner Straße 10, D-80333
München, Duitsland,
Email: a.nuetzel@lrz.uni-muenchen.de
The Late Carboniferous (Desmoinesian, approx. 306 m years) sediments of the Buckhorn Asphalt
Quarry (Oklahoma, USA) contain the best preserved Palaeozoic mollusc fauna world wide. Molluscs
are commonly preserved in original aragonite including shell microstructures, though aragonite is
normally dissolved or recrystallised shortly after deposition. Even larval shells and colour patterns
are preserved. The good preservation of fossils was caused by Ordovician oil which intruded into the
sediments simultaneously to or shortly after deposition, sealing pore space and preventing
recrystallisation via circulating pore waters. The oil then transformed into asphalt loosing its
volatiles.
The fauna of the Buckhorn Asphalt is dominated by mollusc species, especially by cephalopods and
small gastropods. For the purpose of inferring the depositional environment and Palaeoecology, thin
sections were prepared from samples of all main lithologies. Asphaltic rocks were dissolved in a
Soxhlet apparatus using methylene chloride as solvent (asphalt content is up to 20%). The dissolved
samples were sieved (2 mm, 500 µm, 125 µm) and picked. Fossils, especially small gastropods were
documented with SEM- and light microscope pictures. Bioerosion in the Buckhorn fossils is common
and could be proved using SEM-photographs of fossils and casts, as well as with thin sections. At
least 50 gastropod species, two coiled and three orthocone nautiloids have been documented,
however brachiopods and bivalves are rare. The rich marine fauna is furthermore represented by
ostracods, foraminifers, echinoderms, and bryozoans. Vertebrate remains like fish teeth are rare. First
results suggest that most fossils lived in shallow water as is indicated by a diverse assemblage of
bioeroders within the mollusc shells as well as by the presence of large land plant remains. The fossil
material is mixed with siliciclastic sediment which is conglomeratic sometimes, and was transported
over a relatively steep slope or in channels.
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