The earth's climate 450 million years ago (the Ordovician period) is one of the big unknowns.

As time passed there was a possible lowering of local temperatures in the succeeding Ordovician period.

Lingula is known to have existed since the early Ordovician period.

They have changed little in appearance since the Ordovician period, 450 million years ago.

Similar conditions and wildlife remained in place during the early part of the ensuing Ordovician period.

This also marks the end of the Ordovician period.

The earliest fossil of fungi appears about 460 million years ago in the Ordovician period.

The lake is located on paleozoic limestone of the Ordovician period.

This order dates back to the lower Ordovician period.

Their fossil record extends back to the Ordovician period (460 million years ago).