A paleobiogeographical scenario for the Taxaceae based on a revised fossil wood record and embolism resistance

Abstract

Fossil Taxaceae are documented for the Cenozoic throughout most of the northern hemisphere, but the pre-Cenozoic history of this group is still poorly known. The fossil wood record is difficult but can shed light on this history. We critically evaluated the fossil woods assigned to Taxaceae and then compared the fossil record of taxaceous woods to the fossil record of taxaceous leaves and reproductive structures. We then considered the fossil record in the context of family's molecular phylogeny. More than half of the fossil woods attributed to Taxaceae lack diagnostic characters of the family (longitudinal tracheids with helical thickenings and abietoid pitting on radial walls). Fossil wood that can be attributed to the fossil genus Taxaceoxylon, as well as some specimens placed in the genus Protelicoxylon, which differ only in having mixed type of intertracheary radial pitting, probably belong to Taxaceae. The fossil wood record, as reappraised, is not informative about the history of individual genera within the family, but fits that of leafy remains. Taxaceae wood shows remarkable resistance to embolism and subsequent increased risks of conduit implosion that might be prevented by the presence of tertiary helical thickenings. Our findings suggest a paleobiogeographical scenario for the Taxaceae, that involved a Western Europe Early Jurassic cradle and expansion to their Holarctic modern distribution.