A rookery is a colony breeding rooks, and more broadly a colony of several types of breeding animals, generally gregarious birds. Coming from the nesting habits of rooks, the term is used for corvids and the breeding grounds of colony-forming seabirds, marine mammals (true seals or sea lions), and even some turtles. Rooks (northern-European and central-Asian members of the crow family) have multiple nests in prominent colonies at the tops of trees. Paleontological evidence points to the existence of rookery-like colonies in the pterosaur Pterodaustro. The term rookery was also borrowed as a name for dense slum housing in nineteenth-century cities, especially in London.