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
