Geology Reference
In-Depth Information
Chapter 7
Molecular Preservation of Eurypterids
Abstract
The fossil remains of eurypterid cuticles, yield long-chain (<C
9
to C
22
)
aliphatic components during Pyrolysis-Gas chromatography-mass spectrometry,
similar to type II kerogen in contrast to chitin and protein that constitutes the bulk
of modern analogs. Structural analysis (thermochemolysis) of the eurypterid cuticle
revealed fatty acyl moieties (derived from lipids) of chain lengths C
7
to C
18
, with C
16
and C
18
being the most abundant. The residue was immune to base hydrolysis, indi-
cating a highly recalcitrant nature and suggesting that if ester linkages are present in
the macromolecule, they are sterically protected. Some samples yielded phenols
and polyaromatic compounds indicating a greater degree of aromatisation, which
correlates with higher thermal maturity as demonstrated by Raman spectroscopy.
Analysis (including thermochemolysis) of the cuticle of modern scorpion and
horseshoe crab, living relatives of the eurypterids, showed that C
16
and C
18
fatty acyl
moieties likewise dominate. Assuming that the original composition of the euryp-
terid cuticle was similar to that in living chelicerates, fossilization likely involved
the incorporation of such lipids into an aliphatic polymer.
Keywords
Marine Sea scorpion Aliphatic Fatty acid Raman spectroscopy
Introduction
In this chapter the chemistry of eurypterid cuticles from a range of localities
(Table
7.1
) is analyzed and compared to the composition of the cuticle of their
modern relatives—scorpions and horseshoe crabs—in order to interpret their
molecular preservation. Eurypterids, known also as sea scorpions, are extinct
aquatic arthropods belonging to the Chelicerata. They fi rst appeared in the Middle
Ordovician, peaked in diversity in the Late Silurian, and became extinct towards
the end of the Permian (Plotnick
1999
). The large number of mainly Silurian spe-
cies makes the eurypterids the most diverse Paleozoicchelicerate group. About
30 % of eurypterid genera include representatives over 80 cm long (Briggs
1985
).
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