Evolutionary history, biogeography, and extinction of the Cretaceous cheirolepidiaceous conifer, Frenelopsis

Frenelopsis Schenk (family Cheirolepidiaceae†) was among the most widespread conifer genera and a dominant element of wetland ecosystems in low to mid-palaeolatitudes in the the Northern Hemisphere. It was also one of the more important peat-forming shrubs and trees generating extensive deposits of Cretaceous lignite. The genus became extinct at the end of the Cretaceous. Studies of the presence/absence and diversity of Frenelopsis allow us to analyse its evolutionary history, biogeography, and the consider the possible causes of its extinction. During the Early Cretaceous, the genus diversified, triggered by the rise of short-lived species and the constraint of endemism. The maximum diversity and species richness were attained in Barremian and Aptian times while the maximum number of global occurrences is documented during the Albian. In the Late Cretaceous, Frenelopsis species richness declined and the genus became progressively more restricted to the Tethyan archipelago in the context of the rise to dominance of angiosperms. In the Maastrichtian, the last representatives of Frenelopsis survived in the coastal wetlands of Iberia as a relictual plant. In northeast Iberia (present-day Pyrenees) the last occurrences from this genus are early to middle Maastrichtian in age and show an intriguing contrast between the abundance of vegetative remains and the lack of Classopollis pollen grains. These data suggest that at the end of its lineage, the plant was reproducing only vegetatively and that male sterility may have contributed to extinction.