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  3. The World of the Flat-footed Fly George Poinar has been fascinated by amber, and the insects embedded in it, since childhood

The World of the Flat-footed Fly George Poinar has been fascinated by amber, and the insects embedded in it, since childhood

admin2010-08-04  14
问题                 The World of the Flat-footed Fly
    George Poinar has been fascinated by amber, and the insects embedded in it, since childhood. Now a professor of entomology at the Berkeley Campus of the University of California, he has successfully  combined these interests to produce Life in Amber, a scholarly and yet very readable book. In it he tells the story of this curious, almost magical substance and the unique record of fossilized life that became trapped and entombed in the sticky resin as it oozed from the forest trees of the ancient past.
    Amber has been endowed with special worth from prehistoric times, Adornments of amber have been found that date back as far as 35,000 BC, and in 1701, King Frederick I of Prussia commissioned  an entire room made of amber as a gift for Peter the Great of Russia. Historically that probably represented the peak of value for amber. Since then our appreciation of it as a decorative material worth its weight in gold has declined somewhat. In Victorian times amber beads had something of a renaissance as an adornment. It now holds greater value as a potential store of fossil DNA.
    Scientific interest in amber has also fluctuated. The embedded small organisms, particularly insects  but also frogs and feathers, have always been part of amber’s allure. In the first century AD, Pliny noted that amber was the discharge of a pine-like tree, originated in the north and often contained small insects. It was not until the 19th century that collection of the amber flora and fauna really got under way. The largest hoard was of Baltic origin, amassed by Wilhelm Stantien, an innkeeper, and Moritz Becker, a merchant. They took their collecting seriously and used mining techniques to extract pieces of amber from clays of Tertiary age that had formed during the Eocene, 38 million years ago, in the Samland peninsula, near Kaliningrad (the former Kbnigsberg) on the Russian Baltic seaboard. Their efforts resulted in about 120,000 amber-embedded animal and plant fossils. These were housed in the Geological Institute Museum at Kbnigsberg University. Unfortunately, despite being dispersed for safety during the Second World War much of this amazing collection was lost.
    Although the depth of this unique view of the insect life in Baltic forests of Eocene age is sadly no longer available in a single collection, we can see something of it. There are still large collections of Baltic amber in public museums around the world but even in total they do not amount to much more than that one unrepeatable collection. The Natural History Museum in London has a "mere" 25,000 specimens.
    Popular misconceptions about amber exist; for example, suggesting that it is the fossilized resin of coniferous trees from the Baltic region, and that its abundance is the result of some unusual condition of these ancient trees. It is true that an astonishing amount of amber has been recovered from this region. However, the most likely candidate to have produced the Baltic amber is an araucariacean tree similar to the living Agathis from New Zealand, which secretes resin. This could well accumulate in this order of magnitude, given the geological time scale of hundreds of thousands, if not million of years. And, as Poinar discusses, the Baltic region was only one of many different areas, on a worldwide scale, from the Dominican Republic, which is his own favourite hunting ground, to China and Romania, that produced amber in Tertiary times.  Furthermore, amber resin producing trees are shown to have an extended geological history extending back to Cretaceous times, more than 100 million  years ago and possibly as far back as the Carboniferous ( more than 300 million years ago ). Many of these older ambers have not been rigorously investigated with modem techniques but Poinar has collected all the available published knowledge on their biological content.
    If you want to know about the record of the Mycetophagklae (hairy fungus beetles  or the Platypezidae( flat-footed flies) in amber, this is where to look. Amber does provide a uniquely wellpreserved  view of the past. And we can see them all in amber from the parasitic wasp larva and its spider host to the flies the spider trapped. Poinar’ s book is a slightly curious mixture of academic taxonomic treatise on the biology of amber and a fascinating semipopular account of how, where and when amber has been produced. But it is by far the best available, well-written and illustrated by a biologist, who is an active and major contributor in the field.
    As the last chapter on the implications of this type of preservation and the prospects for palaeobiological  research intimates, amber is perhaps only just beginning to show its worth.
    Since Poinar wrote Life in Amber, two independent teams of American investigators have extracted  and sequenced the oldest known DNA from insects trapped in Dominican amber, more than 30 million years ago. Poinar was one of them.
Poinar has gained ail the published information concerning those older ambers’__________.
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答案biological content
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