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Decay of crustacean cuticle in previous experiments resulted in extensive loss
of the protein component within the fi rst 2 weeks, while chitin remained largely
intact for the fi rst 8 weeks, attesting to its greater survival potential (Stankiewicz
et al.
1998a
). Traces of chitin are present in Pleistocene beetles (Stankiewicz
et al.
1997a
) and in weevils as old as 25 million years (Stankiewicz et al.
1997b
;
Gupta et al.
2007a
). However, the cuticles of fossil arthropods older than the
Tertiary show no trace of chitin or protein (Briggs et al.
2000
), but have a domi-
nant aliphatic component similar to type I/II kerogen (Briggs
1999
) at times
partially interlinked by fatty acyl moieties (Gupta et al.
2007a
). Selective preser-
vation of resistant aliphatics is not a plausible explanation as they do not occur in
the exoskeletons of modern arthropods. Initially, the aliphatic composition was
interpreted as the result of diagenetic replacement by aliphatic organic matter
from an external source (Baas et al.
1995
). However, recent research makes this
argument untenable (see discussion in Briggs
1999
; Gupta et al.
2007a
). Arthropod
cuticles have surface waxes composed of hydrocarbons and fatty acids (Howard
and Blomquist
2005
) that are labile, i.e., extractable/hydrolysable. Thus, it has
been suggested that the aliphatic composition of the fossils was generated by
in
situ polymerisation
of constituent cuticular waxes (Briggs et al.
1998
; Stankiewicz
et al.
2000
).
Taphonomic experiments have been used to investigate the various parame-
ters that control the preservation of arthropod cuticles in the fossil record
(modern shrimp: Briggs and Kear
1993
,
1994
; Baas et al.
1995
; Hof and Briggs
1997
; Sagemann et al.
1999
; cockroach: Duncan et al.
2003
). The emphasis of
these studies was on controlled necrolysis and/or the effect of transportation on
disarticulation. Few experiments have addressed changes in the chemistry of
modern arthropod cuticles to explain their composition in the fossil record.
Stankiewicz et al. (
2000
) used artifi cial maturation techniques in a preliminary
study of the transformation of the cuticle of the emperor scorpion
Pandinus
imperator
. An aliphatic composition was generated but the investigation did not
determine the source of the aliphatic components. Similar experiments have
been used successfully to investigate the origin of aliphatic constituents in fossil
plants (Gupta et al.
2005
,
2007b
). Here we describe an experimental investiga-
tion, using similar artifi cial maturation techniques, to determine the source of
the aliphatic component that accounts for the long term organic preservation of
fossil arthropods.
Material and Methods
The living arthropods
Pandinus imperator
(emperor scorpion),
Crangoncrangon
(shrimp) and
Gromphadorhina portentosa
(Madagascan hissing cockroach) were
investigated as they all belong to groups with a well-documented fossil record that
have been the subject of taphonomic experiments (Briggs and Kear
1993
,
1994
;
Sagemann et al.
1999
; Stankiewicz et al.
1998a
; Duncan et al.
2003
). The large size
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