The Australian Tertiary plant fossil record documents rainforests of a
tropical to temperate character in south-eastern and south-western Au
stralia for much of the Early Tertiary, and also shows the climaticall
y mediated contraction of these rainforests in the mid to Late Tertiar
y. The fossil record of Australian monsoon forests, that is semi-everg
reen to deciduous vine forests and woodlands of the wet-dry tropics, h
owever, is poorly known. Phytogeographic analyses have suggested an im
migrant origin for some floral elements of present day monsoon forests
in northern Australia, while other elements appear to have a common h
istory with the tropical rainforests sensu stricto and/or the scleroph
yllous flora. Early Tertiary macrofloras in northern South Australia m
ay provide some insight into the origins of Australian tropical monsoo
n forests. The Middle Eocene macrofloras of the Poole Creek palaeochan
nel, and the ?Eocene-Oligocene silcrete macrofloras of Stuart Creek, b
oth in the vicinity of modern Lake Eyre South, have foliar physiognomi
c characteristics which distinguish them from both modern rainforest a
nd Eocene-Oligocene floras from south-eastern Australia. Preliminary s
ystematic work on these floras suggests the presence of: (1) elements
not associated today with monsoon forests (principally 'rainforest' el
ements, e.g. Gymnostoma, cf. Lophostemon, cf. Athertonia, Podocarpacea
e, ?Cunoniaceae); (2) elements typical of both monsoon forests and oth
er tropical plant communities (e.g. cf. Eucalyptus, cf. Syzygium, and
Elaeocarpaceae); (3) elements likely to be reflecting sclerophyllous c
ommunities (e.g. cf. Eucalyptus, Banksieae and other Proteaceae); and
(4) elements more typically associated with, but not restricted to, mo
nsoon forests (e.g. Brachychiton). The foliar physiognomic and florist
ic evidence is interpreted as indicating a mosaic of gallery or riveri
ne rainforests, and interfluve sclerophyllous plant communities near L
ake Eyre in the Early Tertiary; deciduous forest components are not cl
early indicated. Palaeoclimatic analysis of the Eocene Poole Creek flo
ras suggests that rainfall was seasonal in the Lake Eyre area in the E
ocene; however, whether this seasonality reflects a monsoonal airflow
is not clear.