Cycads ‘not ancient’
21 November 2011
New research has found living cycads are not survivors from the time of the dinosaurs, but evolved in the last 10-12 million years – long after dinosaurs disappeared.
An international team of botanists used a ‘molecular clock’ technique on the genes of two-thirds of living cycad species. Because mutations occur at a known rate, they could trace back how long ago different species diverged. They found today’s cycads share a common ancestor some 12 million years old.
Cone-producing cycads are ancient – the fossil record shows they date back at least 280 million years – and were at their most diverse in the Jurassic and Cretaceous periods, when dinosaurs dominated the land. But this study shows none of those species survive, so none of today’s species are true ‘living fossils’.
‘This radically changes our view of these emblematic plants,’ said Dr Nathalie Nagalingum of the Royal Botanic Garden, Sydney, who led the research. ’
Although they're descended from ancient species of cycad (most died out with the dinosaurs in the mass extinction that ended the Cretaceous 65 million years ago) the plants we have today began diversifying at roughly the same time, 10-12 million years ago – a phenomenon Dr Nagalingum believes may have been triggered by a major event, such as the global cooling which happened at about the same time.
However, she also warns current climate change is happening at a much faster rate – one which may be too rapid for slow-growing cycads to survive.’