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rain and summer drought climate analogous to contemporary MTC, complete
with xerophytic plant adaptations and abundant evidence of periodic crown fires
(Allen
1998
). This vegetation dominated by dinosaurs was open low-growing
“chaparral-like,” comprising fire-prone conifers, cycads and ferns subject to peri-
odic fires (Insole & Hutt
1994
; Collinson
et al.
1999
). Charred remains point to
numerous fossils that have been interpreted by Allen (
1998
) as fire adaptations,
including serotinous cones, fire-stimulated hard seeds, and highly sclerotic fern
indusia that were dropped when heated by fire, among others (see Scott
2000
for
other examples of Mesozoic fire-prone environments). We hypothesize that such
fire-prone environments have been present somewhere in the world throughout
much of Earth's history. Even during periods of “equable” climates there have
been gradients in moisture availability, with xeromorphic plants capable of carry-
ing fire.
Early Cenozoic climates are widely considered to have been warm and
humid with relatively little seasonal variability. Nonetheless, deposits from the
Paleocene-Eocene boundary show evidence of widespread fires followed by sea-
sonal rains that generated large charcoal deposits (Collinson
et al.
2007
). Much of
this early history of fire is based on coal petrological analyses and such studies
have not been widely conducted on Tertiary sediments; perhaps as a result we have
far less evidence of fire in the Tertiary than in earlier periods (Scott
2000
).
Paleobotany has tended to emphasize taxonomy of macrofossils and been far less
concerned about indicators of pyric conditions (Robinson
1989
). Thus, while the
Tertiary is represented by numerous fossil floras, nearly all have focused on the
taxonomy of the floras and not on characteristics of the environments that would
pertain to fire.
Perhaps the most extensive Tertiary evidence of fire is in Oligocene and Miocene
coal beds from southeastern Australia and these attest to widespread fires in
seasonally dry sclerophyllous shrublands (Martin
1996
; Kershaw
et al.
2002
).
Clear evidence of fire as driver of ecosystem change comes from the late Miocene,
5-10 Ma, where increased incidence of fires appears to have played a major role in
establishing the dominance of
Eucalyptus
in Australia (Martin
1996
; Bowman
2000
), Also, Miocene coal deposits in Europe reveal a similar story of frequent
fires in seasonally dry shrublands and swamps (Figueiral
et al.
2002
). The late
Miocene rise in marine charcoal deposition (Herring
1985
; Jia
et al.
2003
)is
further evidence of Tertiary fire. However, there is no reason to interpret this as
though Earth suddenly discovered fire in the late Tertiary; rather there appears to
be a substantial change in the amount of fire-prone landscape at that time.
It has been hypothesized that the spread of C
4
grasses during the more seasonal
climate of the late Tertiary was due to this increase in fire activity, which opened
up woodlands and created environments favorable to C
4
grasslands (Bond
et al.
2003
; Keeley & Rundel
2005
). The high productivity and flammability of C
4
grasses would have produced a feedback process that further increased fire activ-
ity, thus maintaining the grassland and savanna landscape. Few other ecosystem
processes can account for the fossil record of C
4
grassland expansion at the
