London mayor Boris Johnson has announced that works by Elmgreen and Dragset and Katharina Fritsch have been commissioned to occupy Trafalgar Square's Fourth Plinth.

Elmgreen and Dragset's Powerless Structures, Fig.101 will take up residence in 2012, replacing Yinka Shonibare Nelson's Ship in a Bottle sculpture. Katharina Fritsch's sculpture of a giant blue cockerel - Hahn/Cock - is set to be unveiled in 2013. Both were among a shortlist of six works for the Fourth Plinth.

Johnson said: "All of the shortlisted artists show what an extraordinary crucible the Fourth Plinth is for contemporary art. "It continues to spark the imagination and there has been a tremendous response from the public."

Fourth Plinth Commissioning Group chair Ekow Eshun added: "Both have created imaginative and arresting artworks that fully respond to the uniqueness of their location." Image: Elmgreen and Dragset's Powerless Structures, Fig.101