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Last Updated: Tuesday, 23 November, 2004, 12:22 GMT
Bees survived dino extinction
Cretotrigona prisca, American Museum of Natural History
Bees were found trapped in amber from the time of the dinosaurs
New evidence shows tropical honeybees survived the post-impact winter 65 million years ago that is thought to have helped kill off the dinosaurs.

An asteroid is thought to have hit our planet at the end of the Cretaceous Period, throwing up dust that blocked sunlight and dragged down temperatures.

Honeybees trapped in amber before the asteroid strike are nearly identical to their modern relatives, data shows.

Details were given at the Geological Society of America's 2004 meeting.

I'm not trying to say an asteroid impact didn't happen...I'm just trying to narrow down the effects
Jacqueline Kozisek, University of New Orleans
The asteroid or comet that created the Chicxulub impact structure in Mexico occurs at the boundary between two geological periods: the Cretaceous and the Tertiary.

This geological boundary marks a mass extinction that wiped out dinosaurs and many other groups of organisms.

The finding throws up all sorts of questions, researchers say, because current models of the post-impact winter suggest global temperatures fell far enough to have killed off honeybees and many of the flowering plants they lived off.

Modern tropical honeybees have an optimal temperature range of 31-34C (88-93F) in order to maintain vital metabolic activities.

This is also the range that is best for their food source: nectar-rich flowering plants.

Temperature sensitive

Based on what is known about the Cretaceous climate and modern tropical honeybees, Jacqueline Kozisek of the University of New Orleans, US, estimated that any post-impact winter event could not have dropped temperatures by more than 2-7C (4-13F) without wiping out the bees.

Current theories about the Chicxulub impact winter estimate drops of 7-12C (13-22F) - too cold for tropical honeybees.

If no modern tropical honeybee could have survived years in the dark and cold without flowering plants, says Kozisek, something must be amiss with the impact winter theory.

"I'm not trying to say an asteroid impact didn't happen," said Kozisek. "I'm just trying to narrow down the effects."

Kozisek dug through the scientific literature to find out what survived the massive extinction event.

"I made a list of all survivors and picked those with strict survival requirements," said Kozisek.

She determined what those survival requirements were by calling on studies of the most similar organisms living today.

She found that tropical honeybees had changed little in 65 million years.

Amber-preserved specimens of the oldest tropical honeybee Cretotrigona prisca are almost indistinguishable from some of their modern counterparts. This means they could even be their ancestors, researchers think.

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