In Australia, researchers precisely dated bone specimens of elephant-size marsupials, giant snakes, huge lizards, and other extinct animals. They found that they disappeared within 10,000 years after humans arrived. Linda Ayliffe of the University of Utah in Salt Lake City said precise dating of rocks and fossils from 27 sites in Australia and West Papua New Guinea clearly showed that large animals there disappeared around 46,000 years ago, or about 10,000 years or so after the arrival of humans. Ayliffe said the dating was significant because some researchers have blamed the extinctions on extended droughts that occurred later. Also, disease is improbable since so many species of reptiles, birds and mammals disappeared at about the same time.
Diseases are unlikely to affect all species the same way.
Ayliffe said it was unlikely that hunting alone led to the disappearance of so many large animals. She said there was evidence that humans 55,000 years ago used fire as a hunting tool, burning vast areas of Australia. Such fires would change the habitat, which would make it difficult for large animals that required plenty of forage to survive, she said. In his study, Alroy created a computer model that factored in such elements as the number of hunters, the number of animals, distribution of prey species, and competition among prey for food. He found that with humans in the equation, virtually every combination was bad news for the big animals of America.