First orchid fossil puts showy blooms at some 80 million...(omprise some 8 percent of all flowering ...)
omprise some 8 percent of all flowering species worldwide.
"Our analysis places orchids far toward the older end of the range that had been postulated, suggesting the family was fairly young at the time of the extinction of the dinosaurs some 65 million years ago," Ramrez says. "It appears, based on our molecular clock analyses, that they began to flourish shortly after the mass extinction at the so-called 'K/T boundary' between the Cretaceous and Tertiary periods, which decimated many of Earth's species."
Orchids, unlike most flowering plants, package pollen in unique structures called pollinia, which consist of relatively large masses of compact pollen grains. The 15- to 20-million-year-old specimen of a worker bee carrying orchid pollinia, recovered by a private collector in the Dominican Republic in 2000, came to the attention of Ram rez and his colleagues at Harvard's Museum of Comparative Zoology in 2005. While this particular species of stingless bee, Proplebeia dominicana, is now extinct, the scientists' analysis of the shape and configuration of its cargo of pollen places it firmly within one of five extant subfamilies of orchids.
The specimen is one of just a few fossils known to illustrate directly a plant-pollinator association. The specific placement of the pollen on the bee's back not only confirms the grains were placed through active pollination -- as opposed to a random encounter with an orchid -- but also sheds light on the exact type and shape of orchid flower that produced the pollen tens of millions of years ago.
By applying the so-called molecular clock method, the scientists also estimated the age of the major branches of the orchid family. To their surprise, they found that certain groups of modern orchids, including the highly prized genus Vanilla, evolved very early during the rise of the plant family.
"This result is puzzling and fascinating at the same time because modern species of Vanilla or
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| Contact: Steve Bradt steve_bradt@harvard.edu 617-496-8070 Harvard University Source:Eurekalert |
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