Distribution of Cutan in Modern Leaves - Biopolymers: A Molecular Paleontology Approach - page 17

Chapter 2
Distribution of Cutan in Modern Leaves
Abstract Cutan, a resistant non hydrolysable aliphatic biopolymer, was fi rst
reported in the cuticle of Agave americana and has generally been considered
ubiquitous in leaf cuticles along with the structural biopolyester cutin. Because
leaves and cuticles in the fossil record almost always have an aliphatic composi-
tion, it was argued that selective preservation of cutan played an important role in
leaf preservation. However, the analysis of leaves using chemical degradation tech-
niques involving hydrolysis to test for the presence of cutan reveals that it is absent
in 16 of 19 taxa (angiosperm and gymnosperm), including many previously
reported to contain cutan on the basis of pyrolysis data. Cutan is clearly much less
widespread in leaves than previously thought and its presence or absence does not
exert any major bias on the preservation of leaves in the fossil record. In the absence
of cutan, other constituents—cutin, plant waxes and internal plant lipids—are
incorporated into the geomacromolecule and contribute to the formation of a resis-
tant fossil geopolymer.
Keywords Aliphatic biopolymers • Algaenan • Aliphatic • Cuticle
Introduction
Leaf fossils (including both complete leaves and their isolated cuticles) are widely
used in applied paleobotany. Jones and Rowe ( 1999 ) provide a useful summary of
many examples. Applications include paleobiodiversity analysis (Burnham 1993 ),
paleoclimate analysis to determine both temperature and precipitation (Wolfe 1995 ;
Wilf 1997 ; Wiemann et al. 1998 ; Jacobs 2002 ; Kowalski 2002 ; Kowalski and
Dilcher 2003 ; Sun et al. 2003 ; Wilf et al. 2003 ; Liang et al. 2003 ; Glasspool et al.
2004 ), understanding plant paleoecology (Burnham et al. 1999 ; Royer et al. 2005 )
and vegetational history (Mai 1995 ; Collinson and Hooker 2003 ; Hill 2004 ),
documenting insect/plant interaction (Glasspool et al. 2003 ), determining vegeta-
tion response to key global change events (Wing et al. 2005 ) and reconstructing