The diverse vertebrate remains from the Upper Cretaceous freshwater
settings at Iharkut, Hungary, contain two fossil groups,
Pycnodontiformes fish and Mosasauridae that are almost exclusively known
from marine palaeo-environments. Hence, their appearance in alluvial
sediments is very unusual. Trace element and isotope compositions of the
remains have been analyzed to investigate the taphonomy and the
ecological differences among the different fossil groups present at
Iharkut.
All examined fossils have undergone post-depositional diagenetic
alteration, which resulted in high concentrations of REE, U, and Fe,
together with almost complete homogenization of delta(18)O(CO3) values.
Similar REE patterns in different fossils suggest a common origin for
all remains, hence the discovered species most likely lived in the same
local ecosystem. Despite partial diagenetic overprinting, the
delta(18)O(PO4) values of the fossils indicate sufficient taxon-specific
isotopic diversity to permit some broad conclusions on the
palaeo-environment of the fossils. In particular, it is apparent that
the isotopic composition of the Pycnodontiformes fish and Mosasauridae
remains is most compatible with a freshwater palaeo-habitat and
incompatible with a marine palaeo-environment. In addition, the Sr
concentration and isotope data indicate that the Pycnodontiformes and
Mosasauridae likely lived predominantly in a freshwater environment and
were not simply occasional visitors to the Iharkut river ecosystem.
Regarding other fossil groups, high delta(18)O(PO4) values of
Alligatoroidea and Iharkutosuchus teeth suggest that these small
crocodile species might have inhabited swamps and ponds where the water
was relatively rich in (18)O due to evaporation. (c) 2009 Elsevier B.V.
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