World Congress of Malacology Antwerp ... - Unitas Malacologica

last 25 years i.e., since SEMs have been used in paleontology. Improved sampling techniques and
sampling effort produced a great amount of new data. Generally, well-preserved small fossil
gastropods with protoconchs are rare. Many or even most newly described gastropod taxa are small.
This suggests that the fossil global gastropod species richness consists to a large part of species with
a small adult size. Most of the published data of minute fossil gastropods come from poorly lithified
clay-stones which commonly represent soft-bottom communities or were transported by mud-flows.
Calcareous rocks are another important source of small gastropods. Here, shells are normally
replaced by Calcite or they are silicified. Calcite replacements may wheather out or can be cracked
out mechanically. Silicified material can be obtained by dissolution of limestones with acids. Shells
with original aragonitic composition become increasingly rare with increasing geological age. They
are quite common in the Cenozoic, rare in the Mesozoic, exceedingly rare in the Late Paleozoic, and
unknown from the Middle and Early Paleozoic. In terms of Paleoecology, the consideration of
microgastropods usually increases species richness in samples distinctly. Even rank abundance and
therefore faunal structure change if species with small adult size are considered. Especially highspired
caenogastropods and heterobranchs which are too small to be found in the field by surface
collections are commonly very abundant at least from the Late Paleozoic onward, as will be shown
with several examples. This indicates that the radiation of both groups initiated earlier than
previously suggested. Ideally, such fossil data should be published with information about the
sampling technique, mesh size, analyzed rock volume and numerical data on the taxa. However, such
data are rarely available in the literature. Moreover, well-preserved microgastropod material is
largely unknown from the Early Paleozoic. Such material is urgently needed because the major
evolutionary steps were taken during that period.
Changes in Quaternary mollusc assemblages in Eastern Hungary in Late Quaternary
Nyilas, István
Department of Evolutionary Zoology, University of Debrecen, Egyetem tér 1, H-4010 Debrecen,
Hungary,
Email: steve@tigris.klte.hu
Hungary played an important role in the Late Quaternary development of the European Mollusc
fauna, as it is located in the central part of Europe and it was not covered with ice even in the coldest
periods of Pleistocene. As a periglacial territory, it has preserved the majority of its earlier fauna and
was also a refuge area for arctic-alpine (Columella columella) and boreo-alpine species (Vertigo
geyeri, Vertigo substriata).
One of the most outstanding faunas of Late Quaternary with a species number over 50, was studied in
one study site in Hortobágy National Park. Hortobágy is a perfectly flat area where some tens of
centimeters difference can greatly influence the moisture content, vegetation and microclimate of the
base, as well as the mollusc fauna forming on it. The quatermollusc assemblages in Hortobágy seem
to have a double character, i.e. besides land species represented in bigger numbers (e.g. Succinea
oblonga, Oxyloma elegans, Cochlicopa lubrica, Columella edentula, Columella columella, Vertigo
substriata, Vertigo geyeri, Pupilla muscorum, Vallonia pulchella, Vitrea crystallina, Trichia hispida)
aquatic species can also be found in one third of the total individual number (e.g. Valvata pulchella,
Bythinia leachi, Anisus leucostomus, Anisus spirorbis, Gyraulus laevis, Pisidium obtusale, Pisidium
casertanum).
The other study site was a typical loess area in the Hajdúság (eastern Hungary), where over 20.000
individuals of the two profiles were analysed. The diversity of this region is low, its fauna was made
up of only land species, the most typical of which are: Succinea oblonga, Columella edentula,
Columella columella, Vertigo parcedentata, Pupilla muscorum, Vallonia tenuilabris.
The mollusc assemblages of the two study sites have been compared. Radiocarbon method was used
to identify their age. For better comparison fine stratigraphic method was used, samples were taken
by 10 centimeters. In addition to the abundance and dominance data we analysed the population
structure of the same species at the two sampling sites (e.g. Succinea oblonga, Columella edentula,
Vertigo parcedentata). The analysis of some aquatic species in the profile at Hortobágy has also been
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