South America is filled with mammals of North American origin but not vice versa – and scientists have figured out why
South America is filled with mammals of North American origin but not vice versa – and scientists have figured out why: Sabre-tooth tiger _Smilodon_ meets the South American marsupial, _Thylacosmilus_. This is a classic image of supposedly 'superior northerners' outcompeting 'inferior southerners', but such meetings actually rarely happened as many of the southern species had …
