Recent Synchronous Radiation of a Living Fossil

Abstract

Modern survivors of previously more diverse lineages are regarded as living fossils, particularly when characterized by morphological stasis. Cycads are often cited as a classic example, reaching their greatest diversity during the Jurassic-Cretaceous (199.6 to 65.5 million years ago) then dwindling to their present diversity of ~300 species as flowering plants rose to dominance. Using fossil-calibrated molecular phylogenies, we show that cycads underwent a near synchronous global rediversification beginning in the late Miocene, followed by a slowdown toward the Recent. Although the cycad lineage is ancient, our timetrees indicate that living cycad species are not much older than ~12 million years. These data reject the hypothesized role of dinosaurs in generating extant diversity and the designation of today's cycad species as living fossils.

Hemisphere-scale differences in conifer evolutionary dynamics

“…1A; see also the expanded version in SI Appendix, Fig. S4), a pattern that is similar to those found in analyses of other nonangiosperm seed plant lineages (17)(18)(19) and is broadly consistent with the paleobotanical record. However, our analyses indicate that the evolutionary dynamics of the conifer lineages inhabiting mainly Southern Hemisphere environments, including both temperate and tropical habitats, differ from those in the Northern Hemisphere lineages.…”

Distribution of living Cupressaceae reflects the breakup of Pangea

“…Previous studies of gymnosperm radiations mostly have inferred Oligocene-age crown groups (14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26), and a recent meta-analysis found a median crown age for gymnosperm genera of 32 Ma, younger than that found for angiosperm genera (25). Our dating of those genera with more than one species in the Cupressaceae similarly suggests relatively recent diversifications (Fig.…”

Thrips pollination of Mesozoic gymnosperms

“…A relationship between Macrozamia and the Lepidozamia-Encephalartos sister clade would suggest a 200-135 Ma (largely Jurassic) age for the "Macrozamia" lineage (41). The oldest documented fossils of this cycad genus are from the Paleogene of Australia (42), suggesting a latter diversification and possibly a rather recent age for Cycadothrips as well (34). Lastly, the abundance and diversity of other cycad hosts, some representing ancient Mesozoic lineages, lack pollinating thrips, consistent with a recent, Australian origin for the Cycadothrips-Macrozamia association.…”

“…Secondly, it may be premature to extend phylogenetic inference (36,37) from the biology of recent Cycadothrips (7,8) to taxa of Mesozoic thrips (38)(39)(40). Current evidence indicates that Cycadothrips may have acquired plant associational attributes with Macrozamia host species relatively recently (34). Thirdly, the three extant species of Cycadothrips live only on species of the Australian genus Macrozamia.…”