They first appeared in the Permian period, 295-248 million years ago.

They were a successful group which lived during the Permian period, about 260 million years ago.

During the Permian period, the state continued to be mostly dry land.

The stone was analyzed to be about 270 million years old from the Permian period.

In geology, the Permian period takes its name from the region.

The first similar fossils date from the Permian period, 270 million years ago.

Later plants from the Permian period did as well.

Montana was covered by the sea again for a short interval of the Permian period.

A gap in the local rock record spanned the Permian period.

By the Permian period the sea had left completely.