Their fossils occur in beds which were deposited in both freshwater and marine environments.

Their fossils occur in beds of both freshwater and marine environments.

The oldest fossils occur in China from about 0.5 million years ago.

In some places fossils or bioturbation occur.

"But you said fossils occur on many worlds."

"A galactic distribution, predicting where fossils occur?"

Its fossils occur worldwide from the Devonian to the Permian periods.

Living fossils may occur regularly in the fossil record, such as the lampshell Lingula.

Their fossils often occur gregariously as they lived, forming beds largely composed of fossil shells.

These fossils occur mainly in Middle Devonian strata.