Earliest Occurrence of Taiwania (Cupressaceae) from the Early Cretaceous of Alaska: Evolution, Biogeography, and Paleoecology

Fertile and vegetative compression/impression remains of Taiwania Hayata (Cupressaceae) have been recovered from a number of Middle Albian (approximately 106 million years old [Ma]) to Cenomanian (99.6 to 93.5 Ma) age deposits from the North Slope of Alaska. These fossils are the oldest known for the genus and extend the fossil record of Taiwania in North America from the Paleocene (65.5 to 55.8 Ma) to the Middle Albian. These fossils provide a basis for re-assessment of the evolution, paleoecology, and biogeographic history of the genus. The fossil record of Taiwania indicates the genus was rare, but distributed throughout North America and Eurasia from Late Cretaceous to the Pliocene (5.3 to 1.8 Ma) time. The spatial and temporal distribution patterns indicate exchange between North America and Asia occurred throughout the Mesozoic and Cenozoic across the Beringian Corridor. More importantly, the distribution of Taiwania indicates that the genus grew and reproduced under a diverse range of climatic and environmental conditions throughout geologic time, including the cold and unique lighting conditions of the polar latitudes. From a physiological standpoint, the ability of Taiwania to tolerate cold to freezing temperatures and its inability to survive periods of extended darkness during the polar winters if temperatures were above freezing support the idea that polar winter temperatures during the Late Mesozoic and early Cenozoic were below freezing. Comparison of the Alaskan fossils with those of T. cryptomeroides Hayata reveals that in all of the features available for study, the fossils fall within the range of size and morphology seen in T. cryptomeroides and are indistinguishable, at least morphologically, from the living species. The remarkable stasis observed in Taiwania demonstrates that the genus has remained morphologically unchanged since Middle Albian time. Consideration of the paleontological, morphological, and molecular data supports the idea that Taiwania diverged early in the evolution of the Cupressaceae.