Eating Down the Food Chain

Europe once teemed with large mammals, including species of elephant, lion, tiger, bear, moose and bison. America was also home to a number of huge and unusual animals: mammoths, dire wolves, lions, giant sloths and others. The same goes for Australia, where giant kangaroos, huge wombats and marsupial 'lions' once roamed. What do these extinctions have in common? They all occurred around when...