Sunday, 12 January 2014

Flowering Forever

The incredible 100 million year old amber fossil
angiosperm Micropetastos burmensis
David Attenborough is famous, amongst other things, for coining the phrase 'the amber time machine.' Simply put, it describes the way that creatures preserved in fossilised tree resin effectively allow us to see into the past at sights and scenes which perished millions, perhaps hundreds of millions of years ago.

Many amber fossils show flies and fleas, and while they are perfectly preserved, they do not tell us that much about the world in which they lived. Yet occasionally the amber time machine offers a wider view: feathers, spider webs, along with lizards have been found.

Now a truly beautiful amber fossil has been discovered which shows us what flowering plants were like 100 million years ago. Discovered in the Hukawng Valley mines in Myanmar, the mid Cretaceous amber nugget contained a single plant stem, now named Micropetasos burmensis, which supported no less than 18 tiny flowers complete with petals, stamens and anthers. What is more, the amber preserved the flowers in the act of pollination, the characteristic which makes these plants, properly called angiosperms, so unique and diverse in the natural world.

'In Cretaceous flowers we've never before seen a fossil that shows the pollen tube actually entering the stigma,' said George Poinar Jr from the Department of Integrative Biology at the OSU College of Science. 'This is the beauty of amber fossils. They are preserved so rapidly after entering the resin that structures such as pollen grains and tubes can be detected with a microscope.' The transfer of pollen to the stigma is the first step of pollination, showing that the plant was beginning to reproduce. What is interesting is that the pollen grains under the microscope appeared to be sticky, yet the flower was attempting self pollination.

The male pollen tube entering the female stigma
Sticky pollen evolved to be able to bind to the hairs and limbs of insects in order to be transferred from the anthers of one plant to the stigma of another. Therefore it is strange that the plant would self pollinate. Possibly it was an alternate survival strategy. Even so it has its disadvantages as self pollination is an asexual form of reproduction and has the effect of slowing the pace of the organism's survival and adaptation rate.

Indeed insect pollination is part of the reason why flowering plants are such beautiful and diverse life forms. 'New associations between these small flowering plants and various types of insects and other animal life resulted in the successful distribution and evolution of these plants through most of the world today,' said Poinar. 'It's interesting that the mechanisms for reproduction that are still with us today had already been established some 100 million years ago.'

It did not take long for angiosperms to become some of the most successful plants on Earth. They passed through the end Cretaceous extinction with little effort and have colonised almost every biome on Earth since. Genetic and fossil evidence suggests that flowering plants first evolved 120 millions years ago. This stunning amber fossil has given as a glimpse of the early years of this long and incredible story.