Discovering the Desert / Change Over Time

Fossilized Protoyucca trunk

Fossilized Protoyucca trunk (Protoyucca shadishii)

This specimen was discovered in northwestern Nevada and dates back to the Middle Miocene epoch (15 million years ago). It is a predecessor of the current species of Joshua Tree (Yucca brevifolia). The layered, dense bundles of fibrous tissue that form the center of the trunk and a rough outer bark layer resemble the modern Joshua tree.

Yuccas do not grow this far north in Nevada today. The climate of the area was likely much warmer in the Miocene, enabling these ancestral yucca to spread north, and then retreat to their present range during the ice age. An alternate explanation is that the now extinct Shasta ground sloth may have been responsible for the plant’s distribution by consuming the fruit and excreting the seeds.

L 27, W 24 cm
Herring Collection
Joshua Tree National Park, JOTR 11837