Terrestrial Palaeoecology and Global Change

200 Valentin A. Krassilov. Terrestrial Palaeoecology
This consideration was taken into account in my studies of leaf-margin ratios in the
Cretaceous assemblages of Sakhalin (Krassilov, 1975a) that came from successive horizons
of the facially uniform deltaic to shallow marine deposits. Counting leaf specimens,
rather than species eliminated a potential taxonomic bias. The results indicate a
steady rise in the entire/non-entire leaf ratio from the Coniacian to Campanian, followed
by a gradual decrease in the late Maastrichtian and over the Cretaceous/Tertiary boundary
(Krassilov, 1975a; Fig. 87).
In a similar analysis of the mid-Cretaceous plant assemblages from deltaic to shallow-water
carbonate facies of Crimea, a low of the entire/non-entire ratios falls at the
Albian/Cenomanian boundary, with a rapid rise over the Cenomanian (Krassilov, 1984).
As in the case of cycadophyte index (above), a climatic significance of the leaf margin
ratios was revealed by their parallel changes over time-series of successive plant assemblages
in two distinct vegetation realms.
An elaborate multi-character method of leaf analysis has been introduced by Wolfe
(1992) and extended back in time by Spicer et al. (1996). The method allegedly provides
for a much more detailed climatic inference than any single-character approach. However,
the multiple leaf character/climate correlations are obtained for dominant zonal
types of extant vegetation. Edaphic and seral communities, overrepresented in the fossil
record, tend to develop leaf morphologies different from the bulk of regional vegetation.
Moreover, unlike the extant forms used for comparison, the early angiosperms scarcely
were the canopy trees. Climatic significance of their leaf characters might have changed
with their status in the contemporary vegetation structures.
Leaf characters may persist despite of climate change due to their preadaptational
value, as in the case of transition from sclerophylly to xerophylly (III.3.1). Since leaves
Fig. 87. Leaf margin as a climate indicator: ratios (%) of entire-margined leaves in consecutive Cretaceous
assemblages, western Sakhalin. (Cn) Coniacian, (St) Santonian, (Cmp) Campanian, (Mst) Maastrichtian,
(Dt) Early Palaeocene (Danian).