Imagine you were the only person in the world who spoke a specific language, and no one could ever understand you. Welcome to the world's loneliest whale.
In February 2019, NASA said that it would make one more attempt to contact its record-setting, but quiet, Mars rover before pronouncing it dead after 15 years.
Toughie was the world's last Rabbs' fringe-limbed tree frog, which was often found gliding from one tree to another in Panama's rain forest.
The Curiosity rover has been alone on Mars for over seven years, many light-years away from Earth, but how lonely can a robot get?
Sudan, a northern white rhinoceros, was brought to the Ol Pejeta Conservancy in Kenya in 2009, together with one other male and two females who had avoided mass hunting.
The Tree of Ténéré in the Sahara was once the solitary tree for 400 kilometers (250 miles) and stood alone for decades. It most likely grew with many others before the desert became a desert, but it became the sole survivor after a well dug in 1938 provided it with a consistent source of water.
His name suggests how lonely this Pinta Island Tortoise (Chelonoidis abingdoni) from the Galapagos was. Lonesome George was the last of his kind.