Over a period of several hundred thousand years, many visitors dropped into Leaena's Breath cave beneath the Nullarbor plain in southern Australia but never left. The remains of these hapless animals, in this and two associated caves, constitute a palaeontological bounty for understanding past conditions in the region during the middle Pleistocene. The discoveries and their environmental context are described by Gavin Prideaux and colleagues elsewhere in this issue (G. J. Prideaux et al. Nature 445, 422–425; 2007).

The small entrance to Leaena's Breath cave was the undoing of a large number of mammals and reptiles. They evidently fell through this hole, dropping some 20 metres to the cave floor. If they were not killed by their injuries, they later died of thirst. By far the commonest remains are fossils of various marsupials such as wombats, opossums and especially kangaroos; many species of these animals were previously not known, and many did not survive the Pleistocene. Prideaux et al. applied a battery of techniques to date the fossils and the layers in which they were buried. Their results produce ages ranging between 780,000 and 200,000 years ago.

The Nullarbor plain is vast and empty, and today appears as it is in this photograph: flat, dry, shrubby and almost treeless. From their analyses of isotope ratios in samples of herbivore tooth enamel, both ancient and modern, and the faunal composition, the authors conclude that in the past the Nullarbor had a more diverse flora, and a mixture of woods and shrubland that contained more plants with palatable leaves and fruits. But given that the species that did become extinct seem to have been as well adapted to dry conditions as those that did not, the authors also think the environment was as arid then as it is now.

Credit: G. J. PRIDEAUX

Instead of invoking climate change, that common suspect, they argue that the best explanation for the different flora was an increased incidence of bushfires. The result is the impoverished, but more fire-resistant, vegetation of today.