Fossilised Bee Provides Clue to Orchid Evolution
Scientists working at Harvard University have published evidence suggesting that Dinosaurs could well have enjoyed the sight and smell of orchid flowers. In a report printed in the journal – Nature, the university team led by Dr Santiago Ramirez have estimated that the orchid family may have first evolved in the Late Cretaceous.
An analysis of DNA extracted from pollen found on the back of a fossilised bee (preserved in amber) indicates that orchids could have been well established at the time of the extinction of the dinosaurs 65 mya. The amber that contains the beautifully preserved bee fossil was found in the Dominican Republic in 2000. The fossil itself dates back 15-20 million years (Miocene Epoch) and captures a moment in time when a sting less worker bee, got stuck in some pine tree sap having just visited an orchid flower, picking up some of the orchid’s pollen on its back.
The picture above clearly shows the pollen grains preserved on the back of the worker bee. The bee has been identified as a Proplebeia dominicara an extinct species but a close relative to modern bees. The distinctive orchid pollen has been classified to belonging to Meliorchis caribea. Using the DNA extract scientists have been able to calculate the age of the orchid family with greater accuracy, placing the origin of the orchid at between 84 million years ago to 76 million years ago (mya), the Campanian stage of the Late Cretaceous.
Previously, claims as to the age of the orchid family, a plant family that makes up about 8% of all flowering species on the planet, varied widely. Some scientists estimated that they first appeared 112 mya, whilst others claimed that they were much more recent appearing around 26 mya.
Dr Ramirez stated that this wonderfully detailed micro-fossil has provided a fresh insight into the evolution of this diverse group of flowering plants. Many scientists had suspected that orchids were a group of very ancient flowering plants, citing their complex relationships with social insects as evidence of their age. Indeed, the fact that orchids are found all over the world suggest that they first evolved when the continents were joined together in larger land masses such as Laurasia. Orchid pollen is too heavy to be spread by the wind and relies on insect transfer and pollination, therefore it makes sense to suggest that these flowers first appeared when continents like America and Europe were much closer together.
Fossils of orchids are extremely rare, soft plant material is rarely preserved as it is soon broken down and decomposed, the pollen however, is much more robust and much knowledge has been gained by teams of scientists as they assess pollen micro-fossils at palaeontological sites.
It has been reported that orchids become very successful and diversified as a group during the Palaeocene epoch (65mya to 55 mya), the period immediately after the Cretaceous extinction. Just after the K/T boundary (this marks the end of the Mesozoic and heralds the start of the Cenozoic era), 80% of all the pollen micro-fossils are of fern spores. Ferns are often the first plants to re-establish themselves after a natural disaster, this can be seen today as ferns are usually the first plants to re-colonise an area that had been subjected to a volcanic explosion. The large proportion of fern spores in the micro-fossil record has been termed the “fern spike”, but as the world recovered from the mass extinction and the climate became hot and humid, orchid species quickly diversified taking advantage of the favourable climate and the lack of large herbivores.
Perhaps the diversity of orchid species today is a legacy of the mass extinction event 65 million years ago and it is intriguing to think that a dinosaur with its excellent colour vision may have marvelled at an orchid flower just as we do today.