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

Abstract

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