The Christmas Island shrew (Crocidura trichura), once abundant on Christmas Island, has been officially declared extinct. This tiny mammal, which weighed only five grams, was driven to extinction primarily by the introduction of black rats and their parasites, which devastated the island's native fauna. Although the shrew was presumed extinct by 1908, it was rediscovered in 1958 and again in 1984, but efforts to save it ultimately failed. The last known individuals died in captivity, and extensive searches have yielded no further sightings. The extinction of the shrew adds to Australia's troubling record of biodiversity loss, with this being the thirty-ninth mammal species lost since colonization. The story of the Christmas Island shrew serves as a poignant reminder of the fragility of island ecosystems and the consequences of human expansion and neglect.