Tar pit
From Tardis Wiki, the free Doctor Who reference
According to the Tenth Doctor, tar pits were responsible for humans knowing about extinct animals. Beasts of earlier epochs would become trapped in the tar and die, but the tar would preserve the animal's skeleton more or less intact. Some of the most famous tar pits were the La Brea tar pit in Los Angeles, but England was known to have tar pits as well. (NSA: The Last Dodo)
