The Flora of Australia as a Measure of the Antiquity 
of the Angiosperms 
Karl Suessenguth 1 
INTRODUCTION 
If one intends to consider as difficult a 
problem as the early history of a large land 
area, Australia would seem to be particularly 
suitable for such a study: its long geographic 
isolation and the great number of scientific 
investigations to which it has been subjected 
make it a natural choice. 
Australia’s land connection with the island 
groups of Malaysia (except for New Guinea) 
was ended in the Upper Cretaceous period. 
According to physicists’ calculations, based 
on the rates of disintegration of radioactive 
elements, about 30-40 million years have 
passed since the Eocene epoch in early Ceno- 
zoic time. Inasmuch as the Upper Cretaceous 
period occurred before the Eocene epoch, it 
can be concluded that, on the whole, the Aus- 
tralian flora and fauna have remained undis- 
turbed for an extremely long time. Under 
these circumstances of isolation, ancient 
forms of plant and animal life have been 
preserved, while, during the long periods 
since the isolation began, new species of 
plants and animals have developed from 
them as well It must not be forgotten, how- 
ever, that immigration also has occurred, in- 
troducing new species into Australia’s plant 
and animal life since the beginning of its 
geographic isolation. 
The many investigations into the animal 
life of Australia have given unequivocal evi- 
dence of the continent’s isolation. Today the 
most primitive mammals- — the Monotremata 
( Ornithodelphia ) and the species of Echidna, 
Proechidna, and Ornithorhynchus— appear 
1 Botanische Staatssammlung, Munich 38, Ger- 
many. Manuscript received November 20, 1948. 
only in Australia and in New Guinea. These 
mammals resemble reptiles more than any of 
the other mammals because they lay eggs, 
have a cloaca, and still possess the number of 
shoulder bones of primitive animals. As fos- 
sil evidence has shown, their ancestors ap- 
peared during the Triassic formation, to be- 
come, in fact, the first of the mammals. They 
increased in number during the Jurassic pe- 
riod, but, to a great extent, they died out 
as early as the Eocene epoch. In Australia, 
however, some of these primitive mammals 
have survived to this day, affording us illus- 
tration of the concept of "endemism by 
conservation.” 
The marsupials, too, are notably typical of 
Australia. They are not limited to Australia, 
for there are opossums in North and South 
America, and Chironectides in South Ameri- 
ca; but the great majority of the marsupials 
is found only in Australia. They have devel- 
oped there, it is interesting to observe, in a 
manner analogous to the development of 
placental mammals of the other continents, 
notably the carnivores, rodents, insectivores, 
and ungulates. 
The survival of the Monotremata and - of 
the Marsupialia can be attributed to the fact 
that, before man’s appearance on the Aus- 
tralian continent, no other placental mam- 
mals existed in Australia to prey upon them. 
There were only mice, which sometimes 
wandered on driftwood from island to island, 
and bats; but these were not significant ene- 
mies. (It may be possible, of course, that the 
mice and the bats first arrived in Australia in 
times subsequent to the Upper Cretaceous 
period and, therefore, subsequent to the be- 
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