- 1902 – The last known specimens of the Rocky Mountain locust are collected near Brandon, Manitoba.
- 1905 – The last known Honshū wolf of Japan dies in Nara Prefecture.
- 1907 – The huia, a native bird of New Zealand, is last seen. Habitat loss, hunting, and disease all played a role in its extinction.
- 1909 – The last known tarpan, a Polish wild horse, died in captivity.
- 1911 – The last Newfoundland wolf was shot.
- 1914 – The last passenger pigeon, Martha, died in captivity at the Cincinnati Zoo. Excessive hunting contributed to its extinction; it was formerly one of the world’s most abundant birds.
- 1918 – The last Carolina parakeet died in captivity at the Cincinnati Zoo. The bird, formerly inhabiting the southeastern United States, was driven to extinction by exploitation, deforestation, and competition with introduced bees.
- 1924 – The California grizzly bear is sighted for the last time.
- 1925 – The Kenai Peninsula wolf was driven to extinction.
- 1929 – Acalypha wilderi was last seen in the wild. This species may be synonymous with A. raivavensis and A. tubuaiensis, which would mean it is in fact not extinct globally.
- 1930 – Darwin’s rice rat was last recorded in the Galápagos Islands. Its extinction was probably caused by the introduction of black rats.
- 1932 – “Booming Ben”, the last known heath hen was seen on Martha’s Vineyard, Massachusetts.
- 1933 – The cry pansy from Europe becomes extinct due to habitat loss and overcollection in the only place where it grew, France.
- 1934 – The indefatigable Galapagos mouse was last recorded. Its extinction was probably caused by the introduction of black rats.
- 1935 – The desert rat-kangaroo was last recorded.
- 1935 – The Mogollon mountain wolf and the Southern Rocky Mountains wolf were hunted to extinction.
- 1936 – The last thylacine died in captivity. Hunting, habitat loss, disease, and competition from domestic dogs all may have contributed to the extinction of the species.
- 1937 – The Bali tiger was last definitively seen around this time, but likely persisted into the 1940s or possibly even the early 1950s.
- 1939 – The toolache wallaby was last recorded.