Geology Reference
In-Depth Information
Chapter 11
Preservation of Organic Fossils at the Las
Hoyas Formation, Spain
Abstract
Molecular analysis of fossil fi sh scales from the Cretaceous Las Hoyas
Formation revealed a dominant aliphatic composition (C
8
to C
22
) whereas modern
fi sh scale is proteinaceous (largely collagenous). Analysis of the aliphatic polymer
using thermochemolysis revealed the importance of ester linkages; saturated fatty
acids C
14
to C
18
(particularly C
16
) are the most abundant. These acid components and
their unsaturated counterparts are evident in the lipid composition of modern fi sh
scale. Thus, the aliphatic composition of the fossil scales is likely a result of the
incorporation of lipids (including a C
19
aromatic hydrocarbon) from the original
indicating preservation by
in situ
polymerization of labile aliphatic components.
Fossil arthropods and plants from the same deposit also show a dominant aliphatic
macromolecular component, likely derived predominantly by crosslinking of free
lipid precursors. Differences in the relative distribution of molecular components
indicate likely chemosystematic differences between different fossil groups.
Keywords
Fish • Pyrolysis • Lipid • Kerogen • Aliphatic • Konservat-Lagerstätte
Introduction
The Cretaceous lacustrine limestones of Las Hoyas have yielded a well preserved
and diverse biota of plants, crustaceans, insects, fi shes, tetrapods (including the
dinosaur
Pelecanimimus
) and birds (see Fregenal Martínez
1998
for review). Here,
as in the majority of other pre-Tertiary deposits, arthropod and plant fossils are
altered to a macromolecule with a dominant aliphatic component, similar in compo-
sition to type I and/or II kerogens (Briggs
1999
; Briggs et al.
2000
). The aliphatic
composition of such fossils was attributed previously to selective preservation of
resistant aliphatic biopolymers such as cutan (de Leeuw and Largeau
1993
).
However, resistant aliphatic biopolymers are absent in arthropods and in most plants
and preservation of these fossils cannot be attributed simply to selective preservation.
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