Deep Impact?

Why an asteroid impact is unlikely to have caused the Late Quaternary mass extinction.

The Pleistocene world was dominated by large mammals, flightless birds and reptiles. These included mammoths, mastodons, giant ground sloths, camels, sabre-tooth cats, giant beavers, and giant deer with antlers spanning 3 m (10 ft.). In Australia, there lived the hippopotamus-sized Diprotodon optatum that weighed in at 2.8 tonnes, and was the largest marsupial of all time. These animals are collectively known as the megafauna, a term applied to animals with an adult weight of 45 kg (100 lb.) or more. Between 50,000 and 10,000 years ago, many of these great beasts vanished in one of the largest extinction events since the demise of the dinosaurs.
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