Recent synchronous radiation of a living fossil.
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.
Arnold Arboretum of Harvard University, 22 Divinity Avenue, Cambridge, MA 02138, USA. nathalie.nagalingum@rbgsyd.nsw.gov.au
N S
NS
Nagalingum
C R
CR
Marshall
T B
TB
Quental
H S
HS
Rai
D P
DP
Little
S
S
Mathews
D001499:Bayes Theorem; D005075:Biological Evolution; D057231:Climate Change; D032462:Cycadopsida / Q000033:anatomy & histology / Q000145:classification / Q000235:genetics; D053476:Extinction, Biological; D005580:Fossils; D017343:Genes, Plant; D049810:Genetic Speciation; D008969:Molecular Sequence Data; D010802:Phylogeny