I thought the mega fauna were still around when man arrived?

Just found this....

The extinction of the Australian megafauna

The extinction of the Australian megafauna has received much scientific and media attention, particularly after the publication of Tim Flannery's book "The Future Eaters" in 1994. Megafauna were a suite of large animals that disappeared towards the close of the Pleistocene and include the hippopotamus-sized Diprotodon and Zygomaturus, the giant kangaroo Procoptodon, the marsupial lion Thylacoleo, and the large flightless bird Genyornis. Flannery speculated that the megafaunal extinctions were the result of a 'blitzkrieg': overhunting by early human colonisers combined with fire-stick farming practises which changed the ecology of the continent so dramatically that many larger marsupial species were driven to extinction. The blitzkrieg model was arguably fortified by the dating of the extinction of Genyornis (Miller et al. 1999) to about 45,000 years ago in central Australia, though it was claimed that it survived until later in other locations (Field & Boles, 1998). Most recently, Roberts et al. (2001) presented optical dates on sediment layers at a series of sites which contained articulated megafauna remains. They argued that the megafauna went extinct within a short time period at about 46,000 years ago. However, Roberts et al.'s interpretation of the dates ignited a heated debate (e.g. Field & Fullagar 2001, Field & Wroe 2001; Wroe & Field 2001) because of the selective sampling, the effective sample size and the exclusion of any site that did not contain articulated skeletal remains (bones in anatomical order). The latter effectively excluded all archaeological sites. This included Cuddie Springs, where megafauna remains are found in physical association with flaked stone tools over a number of stratigraphic horizons, and dated from about 27,000 to 36,000 years ago (Field & Dodson, 1999; Field et al., 2001). The controversy surrounding Cuddie Springs and similar sites can be resolved by dating the megafauna fossils themselves (Roberts et al. 2001b,c) and examined in the context of other site data (e.g. geomorphology, archaeology etc.; see Field & Fullagar, 2001).

Our research is directed to establish the age of the Australian megafauna sites. U-series dating of eggshells and optical dating of sediments have provided important calibration points for the amino acid study of Miller et al. (1999). ESR dating has shown that some of the "young" megafauna sites, e.g. Lancefield (Huet et al. 1998) or Tambar Springs (Gr¸n, unpublished) are older than about 50,000 years. At the Naracoorte Caves (see Figures 1 and 2), we have used U-series dating as well as ESR dating to establish the the chronology of this World Heritage site back to more than 400,000 years (Gr¸n et al. 2001, Moriarty et al. 2000). Presently, we are collaborating with Judith Field (Sydney University), the Chief archaeologist at Cuddie Springs, to establish the age of the faunal remains of this significant site as well as with R. Wells (Flinders University) on numerous other megafauna sites in Australia.

References:

Flannery, T.F. (1994) The future eaters. Reed Books, Melbourne.
Field, J. & Boles, W. (1998) Genyornis newtoni and Dromaius novaehollandiae at 30,000 b.p. from Cuddie Springs, southeastern Australia. Alcheringa 22: 177-188.
Field, J. & Dodson (1999) Late Pleistocene megafauna and archaeology from Cuddie Springs, south-eastern Australia. Proc. Prehist. Soc. 65: 275-301.
Field, J. & Fullagar, R. (2001) Archaeology and Australian megafauna. Science 294: 7a.
Field, J & Wroe, S. (2001) Mystery of megafaunal extinction remains. Australasian Science 22: 21-25.
Field, J. et al. (2001) A large area archaeological excavation at Cuddie Springs. Antiquity 75: 696-702.
Gr¸n, R., Moriarty, K. and Wells, R. (2001) ESR dating of the fossil deposits in the Naracoorte Caves, South Australia. Journal of Quaternary Science 16: 49-59.
Huet, S.v., Gr¸n, R., Murray-Wallace, C.V., Redvers-Newton, N. and White, J.P. (1998) Age of the Lancefield megafauna: a reappraisal. Australian Archaeology 46: 5-11.
Miller, G.H. et al. (1999) Pleistocene extinction of Genyornis nemtoni: human impact on Australian megafauna. Science 283: 205-208.
Moriarty, K.C., McCulloch. M.T., Wells, R.T. and McDowell, M.C. (2000) Mid-Pleistocene cave fills, megafaunal remains and climate change at Naracoorte, South Australia: towards a predictive model using U/Th dating of speleothems. Palaeogeography, Palaeoclimatology, Palaeoecology 159: 113-143.
Roberts, R.G. et al. (2001a) New ages for the last Australian megafauna: continental-wide extinction about 46,000 years ago. Science 292: 1888-1892.
Roberts, R.G. et al. (2001b) Response to Field & Fullagar. Science 294: 7a.
Roberts, R.G. et al. (2001c) The last Australian megafauna. Australasian Science 22: 40-41
Wroe, S. & Field, J. (2001) Red Herrings and Giant Wombats. Australasian Science (Nov), 22: 18.