In St. Louis de Montfort's The Secret of the Rosary he quotes the Blessed Virgin Mary talking to St. Dominic:
"I want you to know that, in this kind of warfare, the battering ram has always been the Angelic Psalter which is the foundation stone of the New Testament. Therefore if you want to reach these hardened souls and win them over to God, preach my Psalter."
At a recent FNE Timberwolf meeting my brother leader, Mang says that the Angelic Psalter is the Rosary prayed 150 times and the other leader Ricki Ticki says "Oh I thought that was the Psalms themselves". The boys were a bit confused, but we muddled through without intense theological debate.
Now, (not to get all technical and worried about consistencies like I would over Star Wars) if she said that the battering ram has always been the Angelic Psalter, and the Angelic Psalter is the Rosary, then wouldn't the Rosary have had to have pre-existed St. Dominic. But, if it is actually the book of Psalms that Our Lady was talking about, where did tell St. Dominic explicitly to pray the Rosary?