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148 DAVID J. CANTRILL & IMOGEN POOLE

the James Ross Basin. Unfortunately these were

the oldest samples examined, but ?Barremian to

Aptian strata in the South Shetlands lacked

angiospermous grains (Askin 1983). Since these

studies over 250 pre-Albian (e.g. Keating et al.

1992; Duane 1996; Riding et al. 1998; Hathway et

al. 1999), as well as numerous Albian and

younger samples (e.g. Barreda et al. 1999) have

been examined from various parts of the

Antarctic Peninsula. Despite the intensive

sampling of Aptian and older strata, angio-

sperms do not appear in the Antarctic Peninsula

until early Albian times. This event clearly post-

dates their occurrence elsewhere in eastern

Gondwana (Burger 1990, 1993). For example,

angiospermous pollen grains (Clavatipollenites

hughesii) are known from the basal Cyclo-

sporites hughesi Palynozone (early Aptian) of

Australia (Burger 1988), and macrofossils with

attached flowers of Aptian age occur in south-

eastern Australia (Taylor & Hickey 1990). Since

these unequivocal records predate the appear-

ance of angiosperms in Antarctica it seems

unlikely that the Antarctic Peninsula could have

acted as the main biotic gateway for dispersal

across Gondwana, at least in the initial stages of

the radiation. Although it seems certain that

terrestrial land connections occurred between

southern South America and the Antarctic

Peninsula during the Cretaceous, other factors

must have been acting as a barrier to radiation.

The Early to mid-Cretaceous in the southern

hemisphere is marked by strong floral pro-

vincialism (Herngreen et al. 1996). A distinct

floral province dominated by trisaccate pollen

grains characterized microfloras of Australia,

India, New Zealand, southern Africa and

southern South America (Herngreen et al. 1996,

and references therein) (Fig. 5). In particular,

there is a steep floristic gradient through South

America that has been recognized from micro-

floras. For example, in Aptian strata Classopollis

can account for 30-60% of certain palynofloras

by abundance in low latitudes, but drops sharply

in high latitudes, a feature also noted by

Dettmann & Thomson (1987). In the Antarctic

Peninsula region, Classopollis rarely accounts for

more than 5% of the residue and is often absent

(Fig. 6). This type of pattern is repeated for a

number of groups including Elaterate (Gnetales)

and angiosperm pollen. Furthermore the reverse

pattern is true, with some taxa being more

diverse in the high latitudes. For example,

hepatophytes make up to 18% of the within-flora

diversity in high-latitude sites, yet they are

almost absent from mid-latitude floras (Cantrill

1997) (Fig. 6). Similar but less extreme examples

include the ferns and lycopsids.

Equally, within the large Trisaccate Province

that covers Australia, India, New Zealand,

Antarctica, southern Africa and southern South

America there is floristic regionalism. This

phytogeographic floral province can be sub-

divided into two regions: the Cyclusphaera-

Classopollis subprovince (Africa plus South

America), and the Murospora subprovince

(Australia, India) (Herngreen et al. 1996).

Within these two provinces there are important

variations. Microcachvridites antarcticus, one of

the elements that defines the province, typically

constitutes up to 25% by abundance of palyno-

residues at Australian localities (Fig. 5). In

contrast, M. antarcticus is never more than 5-6%

by abundance in the Antarctic Peninsula

microfloras (Fig. 5). These regional differences

also extend to the macrofloras and provide

indirect support for a late arrival of angiosperms

in the Antarctic Peninsula. One group that is

apparently replaced by the angiosperms is the

bennettites. In Australia, bennettites are

common in Valanginian to early Aptian

macrofloras of southeastern Australia but dis-

appear by the Albian (Douglas 1969). In the

Antarctic Peninsula macrofloras, bennettites are

common in the Aptian, and to a lesser extent the

Albian, but they persist until Coniacian times.

This time lag in regional extinction supports the

idea that angiosperms arrived later in the

Antarctic Peninsula region than elsewhere in

Gondwana.

One explanation for the steep floristic gradi-

ents observed through South America and into

the Antarctic Peninsula is a strong climatic

gradient (Dettmann 1986a). Recent climatic

modelling suggests that the thermal and effec-

tive precipitation gradients through this latitudi-

nal transect were extreme (Valdes et al. 1996),

and this is supported by the plant fossils. A com-

parison of Aptian macrofloras between the

Antarctic Peninsula (Cerro Negro Formation)

and southern South America (Baquero For-

mation) indicates important differences.

Antarctic Peninsula floras are high in cool- and

moisture-loving forms (e.g. hepatophytes. ferns,

etc.). In contrast, the Baquero Formation is

dominated by desiccation-tolerant, warm-loving

plants (e.g. bennettites and other seed-plants).

This can be seen in the cuticular adaptations of

the Baquero Formation plants with strongly

sunken stoma, highly papillate leaves and thick

cuticles (Archangelsky et al. 1995). Although

some of the plant groups are represented in both

floras, those such as the bennettites from the

higher latitude sites of the Antarctic Peninsula

have thin cuticles, and appear to lack the

adaptations to cope with warm, desiccating
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