Migration of Organic Molecules from Sediment to Fossils - Biopolymers: A Molecular Paleontology Approach - page 88

pennateraphid and were clearly important in the original depositional environment.
Where plant surfaces are evident, epidermal cell wall outlines are preserved and
possible cuticle remnants are also present. Cellular organisation is suggested in
fractures through specimens. This ultrastructural preservation is inferior to that of
leaves from the Miocene of Clarkia (Niklas and Brown 1981 ; Collinson and Rember,
unpublished). TEM observation confi rms the preservation of internal cellular organ-
isation in plants, although this is somewhat disrupted and discontinuous. A thick
cuticle is preserved on the conifer and a thin and partially fragmented cuticle is
preserved on the dicotyledon leaf. In contrast, the gross morphology of the fossil
weevil is well-preserved; the cuticle is very similar to that of its modern counterpart,
and the sclerotized cuticular components are more or less complete. External sculp-
tural details are preserved along with internal microfi brillar organisation. The fossil
weevils are remarkable for the preservation of a multilayered endocuticle which is
typically lost in arthropods during the early stages of decay.
The high level of molecular preservation for both plant and insect fossils is
clearly indicated by the presence of polysaccharide, protein, chitin and lignin moi-
eties, making the Enspel Formation amongst the oldest known sites for such occur-
rences. However, the polysaccharide and protein moieties may have been chemically
altered during diagenesis and refl ect the composition of melanoidin compounds.
Polysaccharides have been detected in 20 Ka Hymenea subfossils (Stankiewicz
et al. 1998c ) and Pinusleitzeii (6 Mya; Stankiewicz et al. 1997c ). Polysaccharide
markers in the both of these fossils include furaldehyde, furan and pyran markers
along with anhydrosugars. However, no polysaccharide-related moieties have been
reported previously for older fossil leaves.
Similarly, this site contains the oldest known lignin associated with fossil leaves.
The lignin moieties in the Enspel plants include those related to both guaiacyl and
syringyl units. Preservation of lignin in 20 Ka Hymenea was refl ected in both guaia-
cyl and syringyl moieties; however, such moieties were not detected in the same
plant trapped in Dominican amber (25-30 Mya). Lignin markers in fossil 6 Mya
Pinusleitzeii include the guaiacyl markers guaiacol, guaiacylmethane and vinyl-
guaiacol, but syringyl moieties were not observed. Guaiacyl lignin markers along
with C 3 methoxyphenols have also been reported in Miocene Glyptostrobus remains,
and both guaiacyl and syringyl related markers have been detected in a range of fos-
sil leaves in the 8 My old (upper Miocene) Ardèche diatomite (Gupta et al. 2007 )
and in Quercus and Magnolia fossils in the lower Miocene Clarkia deposit (Logan
et al. 1993 ).
The preservation of proteinaceous organic matter in the plant is indicated by the
presence of tryptophan, and this is possibly the oldest documentation of protein
remnants in fossil leaves. The pyrolysis traces of the plants also contain benzene
derivatives; in modern leaves these are indicative of phenylalanine (Gupta and
Pancost 2004 ), but in the fossils they are likely products of diagenetic alteration and
cannot be used to confi rm the presence of proteins. However, these moieties have
been used as protein markers in fossil insects (Stankiewicz et al. 1997a ). Preservation
of proteinaceous organic matter in the insect is indicated by moieties derived from
the amino acids proline, hydroxyproline, tryptophan, tyrosine, and phenylalanine.