Amber-preserved stingless bee carrying pollen packets from the orchid, Meliorchis caribea.
Credit: Santiago Ramirez
Dinosaurs might have gotten a whiff of orchids before the beasts' demise, newfound fossil remains suggest.
Encased in a block of amber, the remains of an extinct, stingless bee (Proplebeia dominicana) with a clump of orchid pollen stuck to its back indicate the flowering plants arose some 76 million to 84 million years ago, much sooner than many scientists had estimated.
"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," said lead study author Santiago Ramirez of Harvard's Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology.
The bee-with-pollen specimen, described in the Aug. 30 issue of the journal Nature, is one of very few fossils that illustrate directly the relationship between a plant and its pollinator, a phenomenon that has fascinated biologists since the time of Darwin.
The specimen was recovered by a private collector in the Dominican Republic in 2000, but it wasn't until 2005 that the sample made its way to the lab of Ramirez and his colleagues.
By analyzing the position and shape of the pollen cargo, the scientists placed the orchid, dubbed Meliorchis caribea, within one of five living subfamilies of orchids.
They conclude the bee acquired the grains through active pollination, as opposed to a random encounter. And in order to transfer the pollen packets to the bee's posterior, the orchid bloom must have been shaped in a particular way in which the anther (the pollen-containing flower part) was bent, the scientists say.
They estimated the specimen to be 15 million to 20 million years old, though its relatives could be placed further back in evolutionary time.
To estimate the ages of the major branches of the orchid family, they compared DNA from the pollen sample with DNA from other orchid species. The so-called molecular-clock method is based on an idea that differences between the DNA molecules of particular species is a measure of how long the two groups have been evolving independent of one another.
The results revealed certain groups of modern orchids evolved early during the rise of the plant family. For instance, they found present-day orchids in the genus Vanilla arose about 60 million to 70 million years ago.
The orchid species began to diversify and flourish, the scientists say, shortly after the dinosaurs went extinct.
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