Cycads not around when dinosaurs roamed

By AAP and AG Staff 21 October 2011
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A new study debunks the idea that modern species of cycads were present at the time dinosaurs roamed the Earth.

IT WAS BELIEVED that dinosaurs in the Jurassic period roamed among them. But now, a Sydney-based scientist says she has proven that modern cycads or `dinosaur plants’ did not grow 200 million years ago.

Dr Nathalie Nagalingum, research scientist at Sydney’s Royal Botanic Garden said that for her study, she look at the plant’s ‘molecular clock’ – a way to age species based on the rate of change in their DNA.

She found that today’s living species are different to those found during the Jurassic period, when dinosaurs roamed.

“We then looked at the extinction of dinosaurs 65.5 million years ago and found there was a gap of 55 million years between when dinosaurs were extinct and modern cycads started to diversify,” she says. “We can now say that living cycad species are not ancient or leftovers from dinosaur times. They evolved independently of dinosaurs only 10 million years ago.”

Cycads not dinosaur plants after all

After studying 11 groups of the plants, Nathalie discovered that all cycads, no matter were they grew, began diversifying 10 million years ago. This indicates a trigger may have been responsible.

“It seems that the trigger was a change in the climate; that is, when global cooling began and when the world started having distinct seasons.”

She says climate change is now threatening the species.

“Today, cycads are listed as [among] the most endangered plants and most likely victims of a mass extinction being caused by humans,” she says. “Cycads are very slow-growing plants so it’s hard to predict whether cycads can survive, now that climate change is occurring at a much faster rate.”

Nathalie’s findings were the result of her research at Harvard University and the University of California, Berkeley, using a combination of fossils and DNA sequences. The study was published in the journal Science this week.