Oral Paper

         Paleobotany

New floral diversity of Lauraceae in the Late Cretaceous

Presenting Author
Keana Tang
Description
Lauraceae comprises up to 3,500 species within about 50 genera and has an exceptional fossil record extending into the Albian of the Early Cretaceous (113-100 Ma). Numerous fossil flowers have been assigned to Lauraceae but their phylogenetic relationships among extant species are poorly understood. Thus, our understanding of the early evolutionary history of this diverse family is limited. Previously, we analyzed phylogenetic relationships of lauraceous fossil flowers using a preliminary genus-level morphological dataset of floral characters, which we revised and used to infer relationships of a new fossil flower. The new fossil is permineralized in a calcium carbonate concretion from Coniacian (89.8-86.3 Ma) deposits of the Eden Main locality in British Columbia, Canada. The specimen was serial sectioned using the cellulose acetate peel technique. The serial sections were studied with light microscopy, imaged, and used to render a 3D reconstruction in Avizo. We analyzed the phylogenetic relationships of the Eden Main flower using a Bayesian total-evidence approach. This dataset was further evaluated by conducting phylogenetic pseudofossilization analyses of living species, which test whether a morphological dataset can accurately recover the positions of living taxa. The new fossil flower is trimerous with two whorls of tepals, two outer whorls of tepaloid stamens, one whorl of fertile stamens, an inner whorl of staminodes, and a superior ovary. The tepal whorls are unequal in size with the outer tepal whorl significantly smaller than the inner whorl. The two outer whorls of the androecium consist of tepaloid stamens with two latrorse anther locules. The third androecial whorl comprises three extrorse bisporangiate stamens with broad filaments that are flanked by paired, peltate staminal appendages. The third whorl alternates with an innermost whorl of sagittate staminodes. The gynoecium consists of a unilocular ovary. Trichomes are present throughout the androecium and inside the hypanthium. These characters indicate the Eden Main flower belongs to Lauraceae and is a new genus based on the combination of unequal tepal whorl sizes, tepaloid stamens, bisporangiate anthers, and peltate staminal appendages. Pseudofossilization analyses recover most extant taxa in their respective tribes with the exception of several taxa that were incorrectly recovered in the morphologically diverse and species-rich tribe Cinnamomeae. This indicates that the current dataset is able to identify crown-group members of Lauraceae and many of its tribes, but that any recovered relationships with tribe Cinnamomeae must be treated cautiously. The Bayesian phylogenetic analysis recovered the Eden Main flower within crown group Lauraceae, but relationships with extant tribes remain uncertain, consistent with the distribution of key traits of the fossil within Lauraceae. While precise systematic relationships of the Eden Main fossil within crown group Lauraceae are yet to be determined, this fossil provides further evidence of the diversification of the family in the Cretaceous.