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Permian plants of Australia

Australian Permian floras

Australian sedimentary basins host fossil plant assemblages from every stage of the Permian. Early Permian floras are particularly well known from the Collie, Perth ,Tasmania , southern Sydney and Bowen basins, and from small exposures near Bacchus Marsh in Victoria. Middle Permian floras are best documented from the Bowen Basin, Queensland. Late Permian floras are extensively represented in the Bowen, Galilee and Sydney basins.

The Australian Permian floras have many genera and families in common with the well-studied Permian floras of India, Antarctica, South Africa, Madagascar and southern South America, but very few taxa are shared with floras from North America, Europe and Asia . This similarity in the floras of the Southern Hemisphere continents and India was one of the key pieces of evidence that led Eduard Suess and several others, to propose in the late 1800s and early 1900s that the southern continents were once amalgamated into a single supercontinent - Gondwana.
 
The Australian Permian floras are dominated by Glossopteris — a distinctive tongue-shaped leaf with net-like veins. Glossopteris and several allied genera are grouped together within the Glossopteridales, an extinct group of Permian gymnosperms. They are often described as “seed-ferns", although the definition of this term has become ambiguous. They have few characters in common with other late Palaeozoic groups described as seed-ferns, but perhaps more in common with enigmatic gymnosperms of the Mesozoic such as Caytoniales. A regular turnover of Glossopteris species is evident throughout the Permian and there are some regional differences in the composition of the floras (McLoughlin 1994a, 1994b; Balme et al. 1995). The Australian Permian floras are generally considered to be of low diversity compared to later Mesozoic floras. However, many assemblages of Permian plants from various Australian basins are currently awaiting description, so the full diversity of the flora is inadequately documented. Glossopteris leaves are morphologically simple so there are few characters that can be used to differentiate species. However, recent studies of the reproductive organs indicate a striking diversity of forms and notable provincialism within the flora (McLoughlin 1990a, 1990b, Prevec et al. 2008).

The Australian Permian floras developed in cool and moist climates at high latitudes (>55°S). The Glossopteris-dominated flora established itself across southern Gondwana in the wake of the retreating ice sheets of the great late Palaeozoic glaciation, which reached its peak around the Carboniferous-Permian boundary. Glossopteris and associated plants grew primarily in vast lowland temperate swamp forests in a range of tectonic settings. Some fossils derive from palaeolatitudes close to the Permian South Pole, revealing that these plants must have experienced several months of winter darkness each year. Glossopteris was a woody, seed-bearing tree, with some species reaching 30 m tall. The fossil leaves are commonly found in dense accumulations representing autumnal leaf banks, and revealing that these plants were probably winter-deciduous. Glossopterid wood has very well defined growth rings that indicate the plants grew rapidly each spring-summer and abruptly terminated growth by the winter.

Glossopteris and its allies were the principal contributors to the vast accumulations of bituminous coals that represent important sources of thermal (steaming) coal for electricity generation and coking coal for metallurgical processing. The local use and export of this coal is a major component of the economies of several Southern Hemisphere nations.

Permian plant fossils have been acquired for the Swedish Natural History Museum by several in-house researchers on expeditions to the Southern Hemisphere, and by exchange of specimens with other institutions. The Museum now has a modest collection of Australian Permian fossil plants (mostly impressions and compressions) from several localities.

 

References

Balme, B.E., Kershaw, A.P. & Webb, J.A. 1995. Floras of Australian coal measures, with notes on their associated Mesozoic faunas. In, Geology of Australian Coal Basins. Ward, C.R., Harrington, H.J., Mallett, C.W. & Beeston, J.W., eds, Geological Society of Australia Inc. Coal Geology Group, Special Publication 1, 41-62.

McLoughlin, S. 1990a. Some Permian glossopterid fructifications and leaves from the Bowen Basin, Queensland, Australia. Review of Palaeobotany and Palynology, 62: 11-40.

McLoughlin, S. 1990b. Late Permian glossopterid fructifications from the Bowen andSydneyBasins , eastern Australia. Geobios, 23: 283-297.

McLoughlin, S. 1994a. Late Permian plant megafossils from the Bowen Basin, Queensland, Australia: Part 2. Palaeontographica 231B: 1-29.

McLoughlin, S. 1994b. Late Permian plant megafossils from the Bowen Basin, Queensland, Australia: Part 3. Palaeontographica 231B: 31-62.

Prevec, R., McLoughlin, S. & Bamford, M.K., 2008. Novel wing morphology revealed in a South African ovuliferous glossopterid fructification. Review of Palaeobotany and Palynology 150: 22-36.