Feldberg et al_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 life-like 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 specimens as well as newly discovered amber inclusions. We provide a survey of all Cretaceous, amber-preserved liverwort species, including 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 nine.基于DNA分析（DNA-based analyses）以及化石记录（fossil record）的研究表明，苔类植物（liverworts）的起源可追溯至古生代早期，但形态逼真的立体化石标本仅见于白垩纪中期以来的琥珀内含物（amber inclusions）中。部分阿尔布阶-森诺曼阶（Albian-Cenomanian）的琥珀保存了被子植物（angiosperms）崛起时期存在的多样生物群组分，这一陆地生态系统发生根本性变革的时期，大概率对附生类群（epiphytic taxa）产生了显著影响。近期相关研究为苔类植物的系统发育分化（phylogenetic diversification）与形态演化（morphological evolution）提供了重要认知。研究显示，白垩纪中期至晚期是物种更替（species turnover）显著的过渡阶段。本文通过检视已有报道的标本与新发现的琥珀内含物，综述了目前所有已被认可的白垩纪琥珀叶苔类植物（leafy liverwort）物种。我们对所有保存在琥珀中的白垩纪苔类植物物种进行了系统梳理，并提供了分类鉴定检索表（determination key）。通过对克钦琥珀（Kachin amber）中26件新化石（包括带繁殖器官的标本）的研究，我们修订了Frullania cretacea、F. baerlocheri以及Protofrullania cornigera的形态描述。白垩纪中期的耳叶苔科（Frullaniaceae）类群往往具备若干现生类群（extant representatives）所不具备的性状及性状组合，这进一步佐证了白垩纪支系更替（lineage turnover）的假说。本次新发现的化石中包含赫氏扁萼苔新种（Radula heinrichii sp. nov.），该新种将保存在琥珀中的白垩纪苔类植物物种总数增至9种。