The passenger pigeon, the Tasmanian tiger, and the Baiji (Yangtze river dolphin) are among the most recognized casualties of what many experts refer to as the sixth mass extinction. This is a consequence of human activities leading to the vanishing of vertebrate animal species at rates hundreds of times faster than their natural pace of extinction.
However, a new study conducted by Stanford University and the National Autonomous University of Mexico, recently published in the Proceedings of the National Academy of Sciences, indicates that the crisis may run even deeper. Each of the three species above was also the last member of its genus, the higher category into which taxonomists sort species. And they aren’t alone.
