Australia: The Land Where Time Began

A biography of the Australian continent 

Australian Cretaceous Vegetation - microfossils

Microfossils

Throughout the Cretaceous, it has been found from microfossils, that southern Gondwana, including Australia, was floristically heterogeneous. Mostly, it was forested, but with areas where there were some patches of woodland, heathland and aquatic communities. Podocarps and Araucarias were an important canopy component in the high latitude forests that had an open structure. By the latest Barremian (125-119 Ma)-Aptian (119-113 Ma) herbaceous and shrubby angiosperms had invaded the understorey communities on the fringes, and associated with the forests of the earliest Cretaceous, and angiosperms had become part of the canopy by the Santonian (87.5-83 Ma).

Australia was on the periphery of the southern portion of Gondwana. It is believed the earliest angiosperms invaded from northern Gondwana across other continental landmasses that were part of Gondwana at the time, and not from Southeast Asia. The Barremian was the latest that it is believed the first wave of migrating magnoliid angiosperms occurred, at a time of lower sealevels and early in the opening of the Indian Ocean and the South Atlantic.

During the Mid Albian (113-97.5 Ma)-Cenomanian (97.5-91 Ma) another wave of migrating angiosperms included non-magnoliid lineages that had evolved in the Aptian in northern Gondwana, arrived in Australia. After the marine regression of the the Aptian seas, the angiosperms invaded the shoreline communities in intracratonic basins of the widening floodplain of the Austro-Antarctic rift valley. During the Turonian (91-88.5 Ma)-Masatrichtian (73-66.4 Ma), migration of angiosperms from northern Gondwana continued, with concurrent in situ evolution and differentiation of austral groups in the Australian-Antarctic region. Evolution and diversification have been identified in 2 foci, one diversification centre, possibly the cradle of Ilex, of the Proteaceae was the area surrounding the embryonic Southern Ocean. A diversification centre for early Nothofagus has been identified in the region of southern South America and the Antarctic Peninsula during active phases of tectonic and Volcanic activity.

Takhatajan (1969) proposed that Australia was a centre of origin where the early angiosperms arose. The pollen evidence does not support this proposal, but it does support the Webb et al.' (1986) thesis that Australian rainforests are remnants of the heterogeneous Gondwanan flora (Dettmann, M.E., 1994). In northeast Australia, where the temperate climate is believed to be similar to that of the Late Cretaceous in the the likely cradle region in southern Australia, there is a concentration of several rainforest proteaceous elements with a history in the Cretaceous. The present distribution at higher latitudes and/or altitudes, at least partially reflects the cooler climates under which  the Nothofagus, and possibly some Podocarps differentiated. The Late Cretaceous pollen record also shows evidence of the evolution of sclerophylly. It is believed these sclerophyllous taxa were probably components of communities on the forest fringes on waterlogged or nutrient deficient soils (Specht, 1992).

Macrofossils

Sources & Further reading

1. M.E. Dettmann in Hill, Robert S., (ed.), 1994, History of the Australian Vegetation, Cambridge University Press.
2. Takhatajan, A., 1969,flowering Plants: Origins and Dispersal. Edinburgh: Oliver & Boyd.
3. Specht, R.I., Dettmann, M.E. & Jarzen, D.M., 1992, Community associations and structure in the Late Cretaceous vegetation of southeast Australasia and Antarctica. Palaeogeography, Palynology, Palaeoecology, 94, 283-309.

• Australian Palaeoclimate during the Tertiary
• Australian Landscapes - Cretaceous to Recent
• Australian palaeogeography - Cretaceous to Recent
• Australian Cretaceous Vegetation - Microfossils
• Australian Cretaceous Vegetation -Macrofossils
• Australian Phytogeography - Tertiary