Fossil woods from the eocene clarno formation of Oregon

Abstract

Eleven species of fossil wood from the Eocene Clarno Formation of eastern Oregon, U.S.A. are described. Six are assigned to extant genera as their anatomy does not differ significantly from present-day species of that genus. Three belong to families in which the anatomy of modern day genera overlap and, consequently, it is not possible to determine the generic affinities of the fossil. Two woods are assigned to extinct genera as they differ significantly from any extant genus. This assemblage of fossil woods indicates that by the Eocene wood in some taxa had reached present-day levels of specialisation, while in others it was more 'primitive' than at present. These woods provide additional documentation from the fossil record for the validity of some of the generalisations about xylem evolution. Scalariform perforation plates are more common and have more bars in these Eocene woods than in their nearest living counterparts. Ring porosity, long believed to be a derived feature, apparently appears post- Eocene in the oaks.