Expanded character sampling inspired by a new Cretaceous conifer seed cone from California: importance of morphology...

Cupressaceae are unique as a conifer family for their exceptionally high morphological diversity, particularly as expressed in seed cones. Their fossil record parallels this pattern and has yielded morphologies not represented in the modern flora. Describing diversity over the entire geological history of the family and using these data in a phylogenetic framework provides opportunities to explore evolutionary relationships among fossil and extant members to understand patterns of morphological evolution in the family.

We describe a new cupressaceous fossil seed cone from the Early Cretaceous (Albian-Aptian boundary; 125 Mya) of California. We construct a novel set of discrete and continuous characters that sample exclusively seed cone morphology and anatomy to explore the evolutionary relationships of the new fossil among living and extinct Cupressaceae, with emphasis on the taxodiaceous grade.

The seed cone represents a new genus and species, Athrosequoia walkeri Pfeiler et al., and the oldest member of the family having peltate ovuliferous complexes. Athrosequoia walkeri possesses a combination of characters encountered in several living taxodiaceous Cupressaceae subfamilies: Athrotaxidoideae, Sequoioideae and Taxodioideae. This novel combination of characters differentiates it from all previously known genera and consistently supports its stable phylogenetic placement among the taxodiaceous grade.

This study documents additional morphological diversity of taxodiaceous Cupressaceae in the Early Cretaceous. The new character matrix highlights the power of seed cone characters in resolving phylogenetic relationships of fossil species, when combined with tree topology constraints based on results of molecular phylogenetics. Within this framework, additional taxon sampling, alongside denser sampling of morphological characters of living taxa, could provide excellent opportunities to understand both the phylogenetic position of extinct taxa and morphological evolution in the family.