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Arnold Arboretum

Study reveals cycads not so ancient

Cycads tree of life project

October 27, 2011

A breakthrough study of international significance has categorically debunked the widely held belief that today’s cycads existed during dinosaur times.

The leader of the study, Dr. Nathalie Nagalingum, said that a combination of fossil study and DNA sequencing has revealed that contemporary species are entirely different from those growing in the Jurassic period which began 200 million years ago. A research scientist at Sydney’s Royal Botanic Garden, Dr. Nagalingum made her discovery as part of a project funded by the National Science Foundation to resolve all non-flowering seed plants (gymnosperms) on the Tree of Life, an effort coordinated by Arnold Arboretum Sargent Fellow Sarah Mathews and co-corresponding author on this research.

“We looked at the extinction of dinosaurs 65.5 million years ago and found that 55 million years separated their demise and the diversification of modern cycads,” Dr. Nagalingum said. “We can now say that living cycad species evolved independently of dinosaurs. The recent radiation of cycads radically changes our view of these emblematic living fossils.”

Studying all 11 groups and two-thirds of the 300 species comprising the family revealed that all cycads—regardless of where they grew in the world—only began diversifying 10 million years ago. Of additional interest, the findings suggest that all the cycad groups across the globe (in Australia, Africa, Southeast Asia, and Central America) began to diversify at the same time, indicating the influence of a global trigger. “It appears that the trigger was a change in climate,” Dr. Nagalingum said, “as global cooling began and Earth started having distinct seasons.”

Although living cycads evolved relatively recently, their future well being hangs in the balance. Today, cycads are listed among the planet’s most endangered plants, likely threatened with mass extinction through human and environmental pressures. As Dr. Nagalingum explained, “As very slow-growing plants, it’s hard to predict whether cycads can survive now that climate change is occurring at a much faster rate.”

Results of the study were published in Science on October 20. The international research team led by Dr. Nagalingum for the cycad project includes Professor Charles Marshall, University of California, Berkeley; Dr. Tiago Quental, Universidade Estadual de São Paulo, Brazil; Dr. Hardeep Rai, Utah State University; Dr. Damon Little, New York Botanical Garden; and Dr. Sarah Mathews, Arnold Arboretum of Harvard University.

Read more:
Science
ABC Science
Live Science
The Sydney Morning Herald
NPR


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