found in birds and thecodonts , formed by the fusion of the two clavicles . In birds, its function is the strengthening of the thoracic skeleton to withstand the rigors of flight ." Concerning pterosaur clavicles: http://books.google.com/books?id=8CKYxcylOycC&pg=PA206&lpg=PA206&dq=pterosaur+clavicle&source=bl&ots=Soo_dytLd7&sig=_LSbSChj57jfcL4MLZ8ahpUBoug&hl=en&ei=TD6cS8riCo_eNbetweYN&sa=X&oi=book_result&ct=result&resnum=3&ved=0CAsQ6AEwAg#v=onepage&q=pterosaur%20clavicle&f=false "In pterosaurs the clavicle was incorporated into the sternum." "David Unwin, 2006. The Pterosaurs