Before humans arrived in Australia, the continent was a very different place, full of dense forests and massive animals that roamed across the landmass.
These megafauna died out about 45,000 years ago, and the cause has long been the subject of significant debate among scientists. But a new study indicates that human activity, rather than climate fluctuations, might have been responsible for their gradual extinction.
When humans first arrived in Australia, it is highly possible that they hunted the large creatures for food, at least occasionally. And according to the new study, even relatively limited hunting may have been enough to drive most of Australia's largest species into extinction within only a few thousand years.
According to the study, published in the journal Nature Communications, most of the world's largest animals outside of Africa went extinct over the past 130,000 years, due to fluctuations in climate, human hunting, and shifting habitats. One of the most dramatic and relatively quick extinctions in that period happened in Australia, when 85 percent of large mammal species weighing more than 44 kg (about 97 pounds) began to disappear less than 50,000 years ago.
"Whether humans were responsible for the demise of the Pleistocene megafauna across Australia has been debated for many years," lead author palaeoecologist Dr. Sander van der Kaars from the Monash School of Earth, Atmosphere and Environment said in a Monash University statement. "Our study found that the demise of the megafauna in southwest Australia took place from 45,000 to 43,100 years ago and was not linked to major changes in climate, vegetation or biomass burning but is consistent with extinction being driven by 'imperceptible overkill' by humans."
How imperceptible? According to the study, it would have only taken the killing of one juvenile animal per person per decade to completely wipe out the megafauna once humans took hold in the region.
The subject of the megafauna collapse in Australia is still controversial, with many pointing to Australia's general shift to a more arid, desert-like climate 70,000 years ago as partially responsible for the animals' demise. But there is evidence to indicate that early humans would seek out at least some animals as a food source: a study published last year indicated that humans cooked the eggs of a giant bird, Genyornis newtoni.
Before humans arrived on the scene, Australia was home to kangaroos weighing more than 1,000 pounds, 25-foot long lizards, 2,000-pound wombats, and many more huge creatures. The team of researchers confirmed their ubiquity on the continent thousands of years ago by measuring the presence of fungal spores that would have feasted on the dung of the large animals in an ancient sediment core, finding that the spores used to be abundant in the region before rapidly collapsing in conjunction with the megafauna population.
"The abundance of these spores is good evidence for a lot of large mammals on the southwestern Australian landscape up until about 45,000 years ago," Gifford Miller, a researcher in the study said in a Colorado University Boulder statement. "Then, in a window of time lasting just a few thousand years, the megafauna population collapsed."
Determining the precise reasons why the ancient creatures disappeared so quickly would represent an important addition to our understanding of human prehistory, but perhaps more significantly, this sort of examination could lead to a more conscious apprehension of the challenges faced by threatened and endangered species today, thousands of years later.
"The results of this study are of significant interest across the archaeological and Earth science communities and to the general public who remain fascinated by the menagerie of now extinct giant animals that roamed the planet – and the cause of their extinction – as our own species began its persistent colonization of Earth," said Dr. van der Kaars.
New species of turtle found in Papua New Guinea
A new species of freshwater turtle has been discovered in Papua New Guinea, one of a group that would have been present for the full geological formation of its main Pacific island, researchers said.
Mountainous and tropical Papua New Guinea is known for its rich biological diversity, but much of its remote areas are relatively unexplored.
The new turtle is one of three distantly-related species—Elseya novaeguineae, Elseya schultzei and the new Elseya rhodini—found across New Guinea island, according to a recent study published in international journal Zootaxa.
The eastern part of New Guinea island is PNG while the western side is Indonesia.
"The three species evolved from a common ancestor between 17 and 19 million years ago," lead author Arthur Georges from the University of Canberra said Tuesday.
"These ages are quite remarkable and came as a surprise, because it means these turtles have together seen the full geological development of the island of New Guinea.
"The other species of freshwater turtle appear to have arrived after New Guinea had formed much as we see it today," he added.
The newly-discovered turtle species is part of the Chelidae family of side-neck turtles which are restricted to South America and Australia, along with PNG, Timor and Rote in Indonesia.
It was identified as a new species distinct from its distant relatives from genetic and other data and found to be distributed across much of the island, south of the central ranges.
Georges said it was "a very pretty turtle" and that one of its distinguishing features was its reddish colouration.
New Zealand fossils reveal new bird species
Flinders University researchers have contributed to the discovery of a new species of shorebird with the discovery of fossils in Central Otago, New Zealand.
The extinct bird dates from a time when New Zealand was covered in subtropical forests and crocodiles roamed parts of the South Island, and is a "missing link" in evolutionary terms.
In a paper published in the Journal of Systematic Palaeontology, New Zealand and Australian-based scientists have confirmed that the 19 to 16 million-year-old shorebird fossils belong to a group which had been thought to only comprise the Australian Plains-wanderer, one of Australia's most endangered birds, and the South American seedsnipes.
The new species, Hakawai melvillei, has been named after New Zealand ornithologist David Melville to honour his efforts in the conservation of migratory shorebirds.
Lead author Dr Venesa De Pietri, formerly of Flinders and now a Canterbury Museum researcher, says that the team were excited to discover that the fossil shorebird was not a typical wader, but more like an ancestral Plains-wanderer, with some seedsnipe-like features. The Plains-wanderer and seedsnipes are unusual shorebirds as they have adapted well to living on the land.
"We're happy to have found a fossil bird that provides a key morphological link between the two groups. The discovery of Hakawai melvillei has confirmed our thinking that the ancestors of the Plains-wanderer and seedsnipes were wading birds, like most other shorebirds," she says.
"It has also confirmed previous research I've undertaken, with colleagues, that the Plains-wanderer and seedsnipes evolved their terrestrial habits independently."
The discovery sheds light on evolutionary processes at work when South America, Antarctica, Australia, and New Zealand were part of the southern supercontinent of Gondwana. Hakawai melvillei, the Australian Plains-wanderer and the South American seedsnipe are all thought to have originated in East Gondwana.
The Hakawai melvillei probably became endemic to (only occurring in) New Zealand when it drifted apart from the rest of Gondwana.
Flinders University's Dr Trevor Worthy, who led the study, said the discovery adds to an emerging story of New Zealand's important role in the evolution of birds in the Southern Hemisphere.
"Unfortunately, like crocodiles, turtles, and some tropical birds, which once inhabited New Zealand, the lineage represented by Hakawai melvillei is long gone," Dr Worthy said.
"We're not sure what happened, but climatic and geographic changes during that time may have been partly responsible for its demise."