History of Coin: Timeline Style

Here is a timeline showing the world's dominant reserve currencies throughout history. Beginning with the Roman aureus and moving to our own United States dollar. Can you spot the one outlier in the timeline friends??  The one that is different than all the other examples and why that is. 

Click the pic to enlarge, and for a more in depth study of reserve coin here is this link http://www.zerohedge.com/article/history-worlds-reserve-currency-ancient-greece-today