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Solid-state
13
C NMR analysis (Gupta et al.
2007a
), however, revealed a signifi cant
aliphatic content in an analogous investigation of fossil leaves (Gupta et al.
2007b
).
Given the widespread occurrence of aliphatic components in sediments, insect,
and plant fossils, the occurrence of aliphatic components in organic fossils might be
attributed to migration (Baas et al.
1995
; van Bergen et al.
1995
). This possibility,
however, has been countered by a number of considerations: (1) Aliphatic polymers
are characteristically insoluble, and therefore relatively immobile (for discussion
see Briggs
1999
); (2) An aliphatic signal was detected in Tertiary
Hymenaea
leaves
and beetles trapped in amber (Table
7.2
), where they are protected from external con-
tamination (Stankiewicz et al.
1998c
); (3) The aliphatic signatures in co-occurring
plant and insect fossils from the Late Carboniferous of North America are different,
indicating that they could not have been introduced solely from the original
sediment (Stankiewicz et al.
1998a
), and the internal morphology of the cuticle is
altered indicating diagenesis; (4) The composition of artifi cially matured arthropod
tissue is aliphatic (Stankiewicz et al.
2000
; Gupta et al.
2006a
) showing that endog-
enous organic matter can generate an aliphatic composition, as observed in fossils;
(5) Thermochemolysis, providing distribution of fatty acids in fossils (de Leeuw
and Baas
1993
) of co-occurring insect and plant fossils and the associated organic-
rich matrix revealed differences in the distribution of the constituent fatty acyl
components, indicating that the aliphatic component of the fossil differ structurally
from that in rock where the TOC is very high (ca. 20). The TOC of rock that yielded
the eurypterids is ca 0.81 % and provided no yield during pyrolysis, such that migra-
tion is even more unlikely (Gupta et al.
2006a
); (6) Logan et al. (
1995
) showed that
leaf lipids in the Miocene Clarkia strata were concentrated on the leaf surfaces
without migrating into the surrounding sediment. These lines of evidence show that
introduction from other such sources as the host rock is not tenable as an explanation
for the highly aliphatic composition of macrofossils.
Thermochemolysis of the eurypterid cuticles yielded fatty acyl moieties from C
7
to C
18
(Fig.
7.4
) dominated by C
16
and C
18
components. The presence of a very similar
distribution in the cuticle of modern
Limulus
, presumably similar in composition to
that of living eurypterids, suggests that lipids from the cuticle of the once-living
eurypterid were incorporated into the fossil macromolecule. Py-GC-MS of
Pandinus
cuticle by thermochemolysis also yielded C
16
and C
18
fatty acyl moieties similar to
the distribution observed in
Limulus
. Additionally, GC-MS and high temperature
GC-MS analysis of the extractable lipid fraction of the modern scorpion cuticle
showed that the fatty acyl moieties are dominated by long-chain saturated moieties
ranging from C
16
to C
28
, and unsaturated moieties from C
18
to C
30
(Stankiewicz et al.
1998a
,
2000
). After base hydrolysis cleaves ester-bound lipids from the cuticular
matrix, the cuticular fatty acyl moieties consist of C
15
to C
36
saturated and C
16
to C
28
mono-unsaturated components (Stankiewicz et al.
2000
), which may also contribute
to the formation of the aliphatic component.
The presence of fatty acid moieties in the pyrolysates suggests that ester linkages
are important components of the fossils; however, if present, they are immune to
base hydrolysis. This could be the result of steric protection of ester functional
groups by the cross linking of aliphatic chains. Gupta et al. (
2007b
) posited a similar
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