Geology Reference
In-Depth Information
Table 9.1
Molecular composition of graptolites
Sample (Yale Peabody
Museum number)
Age; locality
Composition
Rhabdopleura
Modern
Protein/lipids (e.g. C
16
and C
18
fatty acyl moieties)
Palaeodictyota anasto-
motica
(YPM 205210)
Middle Silurian; Lockport,
New York, USA
n
-alkyl chains (C
9
to C
21
)/fatty
acyl moieties (C
16
and C
18
components most dominant).
Phenols, naphthalene and
benzene derivatives (in relative
abundance minor to aliphatics)
Dictyonema peltatum
(YPM 202222)
Silurian; Wisby; Sweden
Diplograptus
sp
.
(YPM
205225)
Ordovician; Gotska, Sweden
Monograptus instrenuus
a
Silurian; Arctic archipelago,
Canada
Benzene derivatives and
n
-alkyl
chains
Monograptus
b
Silurian; Arctic archipelago,
Canada
Aromatic with
n
-alkyl chains
Amphigraptus
a
Ordovician; Oklahoma, USA
n
-alkyl chains, benzene derivatives
and sulfur bearing compounds
a
After Briggs et al. (
1995
)
b
After Bustin et al. (
1989
)
Analysis of
Monograptus
from the Wenlock Cape Phillips Formation of
Cornwallis Island revealed an aromatic structure with aliphatic Group (Bustin et al.
1989
). Briggs et al. (
1995
) analysed
Monograptus instrenuus
from the same locality,
and
Amphigraptus
sp. from the Caradoc Viola Limestone Formation of Oklahoma
(Table
9.1
), and concluded that the aliphatic material that they discovered in the
periderm could not have been derived from an original proteinaceous material like
collagen. They argued that the material in the fossils must have been introduced
from an external source that included a decay resistant macromolecule. The aliphatic
material might have been derived by diagenetic replacement from algal cell walls,
for example, which were a component of the surrounding matrix (Briggs et al.
1995
).
This was proposed in the light of the prevailing paradigm of organic matter
preservation in sediments as a result of the selective preservation of decay resistant
components (Tegelaar et al.
1989
; de Leeuw and Largeau
1993
; Bass et al.
1995
).
Recent research has shown that selective preservation is not an adequate expla-
nation for the preservation of a number of fossil materials, including leaves (Gupta
et al.
2006a
,
2007a
,
b
) and arthropod cuticle (Briggs
1999
; Stankiewicz et al.
2000
;
Gupta et al.
2006b
). Nor can the preservation of fossil arthropod cuticle be explained
by the introduction of material from external sources: thermochemolysis of co-
occurring insect and plant fossils, and the associated organic-rich matrix, from the
Oligocene Enspel Formation, Germany, revealed differences in the distribution of
the constituent fatty acyl components, indicating that the aliphatic component of the
fossil is at least partly derived endogenously (Gupta et al.
2007b
).
Here we test the hypothesis that the organic preservation of graptolite periderm,
like that of the cuticle of arthropods and leaves (Gupta et al.
2006a
), is a result of
in situ
polymerization of the lipid and other labile constituents rather than selective
preservation of decay resistant components or the introduction of material from an
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