The definition, I suppose, would be many, many organisms across many, many different groups. And that is, really, what we are seeing and that is what… - Elizabeth Kolbert

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The definition, I suppose, would be many, many organisms across many, many different groups. And that is, really, what we are seeing and that is what makes scientists fear ... that we're in a mass extinction. ... About a quarter of all mammals are considered endangered. ... About 40 percent of all amphibians are considered endangered. But we're also seeing organisms, invertebrates, for example, are endangered ... many species of reef-building corals are now considered very, very endangered. So you're seeing extinctions across a wide variety of groups, and that, I think, would have to be one of the defining characteristics of a mass extinction.