Liverworts from Cretaceous Amber

DNA-based analyses as well as the fossil record indicate that liverworts date back to the early Paleozoic, but diverse specimens of lifelike three-dimensional fossils only occur as amber inclusions from the mid-Cretaceous onwards. Some Albian–Cenomanian ambers preserve elements of a diverse biota that existed during the rise of angiosperms, a time of fundamental change in terrestrial ecosystems that likely affected epiphytic taxa. Recent analyses have provided important insight into the phylogenetic diversification and morphological evolution of liverworts. They suggest that the mid- to Late Cretaceous was a transitional time with a significant species turnover. Here, we review all currently recognized leafy liverwort species from Cretaceous ambers based on the examination of previously described fossil specimens as well as newly discovered amber inclusions. Our survey includes a determination key. The study of 26 new fossils from Kachin amber, including fertile material, enabled us to emend descriptions for Frullania cretacea, F. baerlocheri, and Protofrullania cornigera. Mid-Cretaceous Frullaniaceae often possess some characters and character combinations that are absent in extant representatives, substantiating the assumption of a lineage turnover in the Cretaceous. Among the new fossils is Radula heinrichsii sp. nov., which expands the number of Cretaceous, amber-preserved liverwort species to eight.