Fossil record of Celastraceae: evaluation and potential use in molecular calibrations

Abstract

Background: Celastraceae is a morphologically heterogeneous family. For this reason, the inclusion of some taxa within this group is controversial. Recently this problem has become significant since its fossil record is recognized as an important source of information for evolutionary studies, especially those using molecular clocks which require a robust, reliable fossil record. Questions: What are the most reliable fossil records of Celastraceae? What morphological characters are used to assign fossils in the family? Study site and dates: Compilation of records contained in paleontological databases, and paleobotanical literature, covering publications from 1869 to 2018. Methods: Published information on the Celastraceae fossil record was compiled and analyzed using the most recent classification system and specialized literature on the family. Results: A total of 168 fossil records were examined, of which nine are proposed for use as molecular clock calibration points. Each specimen has a description based on a character set used for its identification, a photograph and/or illustration, their geological age is well supported, their geographic origin is known, and the specimens are in accredited home institutions with publicly accessible collections. Conclusions: The identification and establishment of relationships between fossil and extant taxa have important limitations that depend on the critical interpretation of morphology in a phylogenetic context. Therefore, it is essential to incorporate only those morphological studies in Celastraceae that help clarify its fossil record.