LUCID GEMS OF ANCIENT LIFE.

• Author: Werner, Louis

Exquisite Dominican amber fossils reveal a spectrum of prehistoric, largely extinct species, offering modern science a window to the past

TREE RESIN is a remarkable substance. Ancient Egyptians used it to preserve dead bodies. Modern Greeks use it to preserve new wine. Around the world it has been chewed like candy, prescribed as medicine, brushed onto paintings, and offered to the Christ child in the form of frankincense and myrrh. But in the Dominican Republic, tree resin is a time machine, taking you back millions of years into the past.

When certain tree resins congeal, they slowly polymerize into a stiffened substance called copal and, if kept from air, will harden finally into the rocklike gem known as amber. Dominican amber, dating from twenty to forty million years ago, is among the world's most beautiful--transparent, lightly colored in hues from yellow to red to blue, and lacking the air bubbles and impurities that mar specimens from elsewhere.

But Dominican amber is noted for inclusions of another sort. Thousands of insects, plants, and animals--in whole or in part, some extinct and some with close cousins still on earth--became entrapped, entombed, and preserved when the amber was still runny and resinous. Today these specimens are the marvel of paleontologists, who find in the fossils a level of three-dimensional detail and completeness unknown in rock or compression fossils or any other vestige of past life.

No one knows exactly how amber acts as a preservative. Its complicated chemistry has never been synthesized in the laboratory. But three of its properties are key to the fossilization process: It dehydrates the specimen without distorting its morphology, it contains antimicrobial agents to fight organic decay, and it tightly seals against air and moisture.

George Poinar, Jr., is one of the world's authorities on amber fossils. Professor emeritus of entomology at the University of California, Berkeley, he is currently on the faculty at Oregon State University. His recent book, The Amber Forest: A Reconstruction of a Vanished World (Princeton University Press), co-written with his wife, Roberta, an electron microscopist, takes a close look at the web of life dating from the Oligocene. That epoch's biodiversity in the Proto-Greater Antilles, a continent-bridging landmass that sank into the sea and subsequently reemerged as islands, was never to be rivaled. Write the Poinars, "in Dominican amber we have zoos and botanical gardens of the past" that far outshine those of today.

The Poinars' specialty is to establish relationships between a fossil specimen, be it flora or fauna, and the biosphere in which it lived, for which all other evidence is missing. Their working theory is of behavioral fixity: that extinct species were linked to their environment in the past in the same way that their closest living relatives are linked to their environment today.

"Behavioral fixity helps us to re-create a whole web of life from a single specimen," says George Poinar. "If we find only insect A, we can assume it carried parasites B and C and fed on plants D and E." Poinar, who also penned a children's book on amber (The Mysteries of Amber, Geofin Press), says that "it's almost a spiritual experience to examine a fossil specimen that had suddenly been trapped in the amber and realize you are seeing the very moment it died. Those forty million yearn that separate it from you just seem to disappear before your eyes."

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