A new species of Thuja (Cupressaceae) from the Late Cretaceous of Alaska: implications of being evergreen in a polar environment.

A branch bearing a number of seed cones of Thuja L. (Cupressaceae) has been recovered from a Late Cretaceous (Turonian) deposit from the North Slope of Alaska. This reproductive material is the oldest known for the genus and is indistinguishable from the seed cones of most of the extant species of Thuja, indicating that the seed cones of this Alaskan fossil Thuja had attained a modern morphological appearance early in the evolutionary history of the genus. From a physiological standpoint, the ability of modern species of Thuja to tolerate cold to freezing conditions and the ability of fossil representatives of the genus to survive periods of extended darkness during the polar winters supports the contention that the polar winters during the Late Mesozoic and early Cenozoic were cold.