Notes: 1  In 1997, MLB retired Jackie Robinson's number 42 meaning no other player in MLB could ever wear it. However, it was grandfathered to anyone who was currently wearing the number. 2  Mariano Rivera is the only Yankee to appear as an active player while wearing his retired number.
The Ordovician Period. The Ordovician Period lasted almost 45 million years, beginning 488.3 million years ago and ending 443.7 million years ago.* During this period, the area north of the tropics was almost entirely ocean, and most of the world's land was collected into the southern supercontinent Gondwana.
The Ordovician and Cambrian Periods are referred to as the age of invertebrates, with trilobites abundant. In this period, brachiopods became more abundant that the trilobites, but all but one species of them are extinct today. In the Ordovician, large cephalopods developed as predators of size up to 10 meters.