Narwhals (Monodon monoceros) and beluga whales (Delphinapterus leucas) are medium-sized toothed whales and the sole representatives of the Monodontidae family. They are the only toothed whales endemic to the Arctic region. While they are each other’s closest relatives and roughly equal in size, these two species differ in their morphology and behavior. Now, a series of DNA and stable isotope analyses of an anomalous toothed whale skull has allowed researchers to confirm that the two species can interbreed successfully. Read more.