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146 DAVID J. CANTRILL & IMOGEN POOLE

Fig. 5. Floristic provincialism across Gondwana derived from Herngreen el al. (1996). Note the regional
differences in abundance of key trisaccate species such as Microcachyridites antarcticus within the Trisaccate
Province. Histograms show, percentage abundance of M. antarcticus in Lower Cretaceous strata: (A) from
Dettmann & Thomson (1987); (B) southeastern Australia from Dettmann (1986b), central Australia from
Burger (1980).

Bryophytes/Hepatophytes

In the earliest Cretaceous, bryophytes and

hepatophytes form an important and character-

istic component of the floristic diversity. Not only

are they diverse, accounting for up to 20% of the

species (Fig. 4C), but they are also ecologically

abundant ranging from colonizers of fresh

sediment to components of established fern

thickets and forests (Cantrill 1997). Indeed,

many localities are characterized by assemblages

comprising just hepatophytes, where they can

cover individual bedding surfaces for hundreds

of metres. This is also true for other southern

high-latitude sites (e.g. southeastern Australia;

Douglas 1973) and appears to be a phenomenon

of high latitude floras in the early part of the

Mesozoic (Cantrill 1997). The highest hepato-

phyte diversity occurs in the Early Cretaceous

but they rapidly become a minor constituent of

the vegetation by the Late Cretaceous. This

pattern is also reflected in the microfloral

diversity (Fig. 4C).

Conifer ales

Conifers generally maintain between 10 and

20% of the within-flora diversity through the

Cretaceous interval (Fig. 4D). This is apparent

from the microfloral record but is less clear in

the macroflora. The macrofloral record shows a

distinct drop in within-flora diversity in the

mid-Cretaceous. The differences may be due to

wind-dispersed conifer pollen representing a

wider range of plant communities than those

seen in the macrofloras.

Pteridophytes and lycophytes

Macrofloral remains are most diverse in the

Early Cretaceous but decline towards mid-

Cretaceous times (Fig. 4E). Following this

decline ferns recover through the later part

of the Cretaceous (Fig. 4E). This pattern is

supported by the microfloral record, which

suggests that the recovery continues through the

Late Cretaceous (Fig. 4E). Although a number

of groups show a marked decline in diversity

through the Cretaceous (e.g. Dipteridaceae),

other families remain relatively stable (e.g.

Gleicheniaceae). In terms of abundance, ferns

show a similar pattern to the bennettites: they

are extremely common in Aptian and Albian

floras but are less frequently encountered in

Late Cretaceous floras. So, although diverse in

the later part of the Cretaceous, they are

probably less important ecologically.

Angiosperms

Macrofloral remains of angiosperms are not

recorded until the Late Albian (Cantrill &

Nichols 1996) where they make up to 12 % of the

flora. This includes a diversity of habit ranging
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