Description

Cyathea pinnata
Early Eocene
Chuckanut Formation
Racehorse Creek, Whatcom County, WA, USA
Fine 2.7 inch fern on 6 inch slab. Leaf,

Fern.

Cyathea is a genus of tree ferns that dates back to at least the Late Cretaceous.  It appears to have originated in Australasia spreading into South America perhaps via Antarctica.  Those continents were closer together at time but drifting away from each other after the breakup of Pangaea (and then Gondwana) across the Jurassic, Cretaceous, and Paleocene).  The presence of Cyathea in North America in the Early Eocene demands further explanation although worldwide subtropical conditions during that time likely allowed wide dispersal with some help from the wind.