This order contains all species of bustards. They are thickset, rather large land birds and are among the heaviest flying birds. The great bustard (Otis tarda) can weigh up to 21 kilograms, which is a record. They are generally solitary and have an omnivorous diet. They inhabit the grasslands and steppes of Europe, Africa, Asia and Australia. In the past, they belonged to the order Ralliformes with the Gruiformes and some Charadriiformes. Today they are classified as a sister group to the Musophagiformes (turacos).