Geoscience Reference
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phyllocladane, its presence in Devonian sediments
would document that at least the biosynthesis of
abietic acid (if not conifers) already existed in the
Fammenian.
Retene, however, has also been observed in the
extracts of several Lower Palaeozoic to Precambrian
carbonates, where inputs from terrestrial plants are
not likely (Jiang et al. 1995; Zhang et al. 1999).
An algal and/or bacterial source was proposed by
these authors. Consistent with this conclusion,
retene was also observed (although in low amounts)
in the pyrolysates of a green alga and cyanobacter-
ium cultures (Wen et al. 2000). Care is therefore
recommended in the interpretation of the presence of
retene in sediments where inputs from higher plants
are low and, most particularly,
7,9-pentaene) (Vliex et al. 1994; Borrego et al.
1997; Izart et al. 2006) (XXXV-XXXVII; Fig. 1).
The fact that only aromatic compounds are reported
may be due to maturity as Paull et al. (1998)
observed fernenes in very immature sediments of
Triassic age. The aromatic arborane/fernane deriva-
tives were observed to be present in Stephanian
coals from Germany, but almost absent from the
underlying Westphalian coals (Vliex et al. 1994;
Auras et al. 2006). Vliex (1994) related this
feature to the increase of Gymnospermopsida (Con-
iferales) in the vegetation, linked to a transition to a
drier climate. Due to the imprecision on the exact
structure of the molecules, arborane or fernane
derivatives could either originate from higher plant
fernenes or from isoarborinol (XXXIX). The latter
is a compound present in a few angiosperms but
which has been assigned a mostly bacterial origin
(Hauke et al. 1992, 1995; Jaff´ & Hausmann 1995).
As a matter of fact, aromatic arborane/fernane
derivatives have also been observed in several sedi-
ments where terrestrial inputs are seemingly inexis-
tent (Hauke et al. 1992). According to Hauke et al.
(1995), however, the compounds identified by Vliex
et al. (1994) are true fernane derivatives. Recently, a
detailed geochemical and botanical study of these
Stephanian coals allowed Cordaites to be identified
as the source of these fernane derivatives (Auras
et al. 2006).
in Ordovician-
Silurian sediments.
Triterpenoids. The triterpenoids are a very large
family which comprises the well-known group of
bacterial biomarkers, the hopanoids, as well as the
hypersalinity biomarker gammacerane (XXVIII)
(Simoneit 1986). Several higher plant biomarkers
also belong to this family, the most famous com-
pound being oleanane (XXIX) (Simoneit 1986).
According to a recent review of the distribution
of pentacyclic triterpenes by Jacob (2003), some
skeletons are particularly widespread among
angiosperms such as oleanane, lupane, friedelane
and ursane (XXIX-XXXII). At least one skeleton,
the serratane (XXXIII), would be characteristic of
gymnosperms, mosses, ferns, lycopodiophytes and
bryophytes. Although it has been observed in
several angiosperms (and in particular Poaceae),
fernane (XXXIV) is in particular present among
ferns (Jacob 2003). In relation to their abundance
in angiosperms, the occurrence of oleanane, lupane,
ursane and their derived compounds is mostly
restricted to Cretaceous or younger oils and sedi-
ments (Peters et al. 2005). The presence of oleanane
in Carboniferous sediments has however been
described by Moldowan et al. (1994). This was fol-
lowed by a long investigation in order to identify the
source of this compound in Palaeozoic sediments.
Recent studies identified Gigantopterids as the
source of oleanane in Palaeozoic sediments which,
added to morphological arguments, would place
the appearance of the angiosperm lineage before
the Permian (Taylor et al. 2006).
Apart from the rare reports of oleanane, the
terrestrial triterpenoids more often described in
Palaeozoic sediments are aromatic compounds
belonging to the arborane/fernane family which
have been recently named MATH (5-methyl-
10(4-methylpentyl)des-A-25-norarbora(ferna)-5,7,9-
triene), MAPH (25-norarbora(ferna)-5,7,9-triene),
DAPH1 (24,25-dinorarbora(ferna)-1,3,5,7,9-penta-
ene) and DAPH2 (iso-25-norarbora(ferna)-1,3,5,
Skeletal materials
Organisms living on land lack the support of
water to overcome gravity and therefore have to
strengthen or develop supportive tissues. If we con-
sider the present-day skeletal biopolymers, which
are potentially stable enough to survive in the
fossil record on a regular basis and thus potentially
leave a fingerprint of the terrestrialization process,
we often observe these are at the boundary between
the cell/organism inside and its outside and
combine their structural function with protection,
for example, cuticles. They consist of only four
basic building blocks produced by ancient biosyn-
thetic pathways common to Archaea, Bacteria and
Eukarya (Kandler & K¨nig 1998). These building
blocks are sugars, amino acids, long-chain lipids
and aromatics.
Sugars, amino acids and their polymers - chitin.
Among the earliest such structures are probably
the peptidoglycans (amino acid-sugar polymers)
found in the cell walls of Bacteria and Archaea.
Peptidoglycans are known to be resistant to degra-
dation compared to proteins and are observed in
recent sedimentary organic matter (Grutters et al.
2002; Nagata et al. 2003). However, they do not
account for an important part of the organic matter
