Albert Einstein's theory of relativity is actually two separate theories: his special theory of relativity , postulated in the 1905 paper, The Electrodynamics of Moving Bodies and his theory of general relativity , an expansion of the earlier theory, published as The Foundation of the General Theory of Relativity in 1916.
Timber or Grey Wolf. Once the world's most widely distributed mammal, the grey wolf has become extinct across much of its former range and its present distribution is much restricted. Grey Wolf (Canis Lupus), Carpathian Mountains, Romania.
Credit: Mauricio Anton. Saber-toothed cats apparently did not go extinct for lack of prey, contradicting a popular explanation for why they died off, fossil evidence now suggests. Even near their extinction, saber-toothed cats likely had enough to eat, researchers noted. Saber-toothed cats, American lions, woolly mammoths and other giant creatures once roamed across the American landscape. However, at the end of the late Pleistocene about 12,000 years ago, these megafauna went extinct, a die-off called the Quaternary extinction.