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Early Bloomers

Natural History, May, 1999 by William Crepet

A clay pit in coastal New Jersey holds the world's richest trove of fossil flowers.

Flowers instruct us to enjoy the moment, for inherent in their seductive power is the knowledge that neither they nor we will last forever. Recently, however, an ancient marsh in coastal New Jersey has offered up some flowers that have survived a very long time indeed--approximately 90 million years--and that convey a different lesson. Little in these floral remains dating from the Late Cretaceous would be suitable for a lover's bouquet, but beauty of another kind abounds. For the first time in the fossil record, we see a variety of flowers related to such modern-day plants as hydrangeas, carnations, azaleas, pitcher plants, oaks, and the tropical mangosteen. So well preserved are the fossil flowers that not only petals but also pollen grains and even tiny ovules can be seen in detail. Also in the New Jersey deposits are fossilized remains of some of the insects that pollinated these flowers.

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Ninety million years ago, this fossil-rich area (now a sandy clay pit) was part of a delta with ponds and crisscrossing streams leading to the Atlantic Ocean. Rains washed insect and plant remains--including leaves, fruits, and flowers--from nearby uplands into the ponds and streams; much of the detritus floated out to sea, but some settled on the marshy bottom. Within this debris today are fossilized insects trapped in amber and "charcoalified" flowers (the intense heat of a fire can harden plant cell walls, making them impermeable to water--provided they don't catch fire and burn up first). Because the flowers were charcoalified before the muck they were trapped in turned to rock or clay, they never flattened out and are still perfectly three-dimensional.

The New Jersey site contains fossilized flowers from more than two hundred species of angiosperms, or flowering plants--more than in any other known location in the world. Plants with so-called primitive flowers, which lacked adaptations for attracting "advanced" pollinators such as bees, lived side by side with remarkably modern flowers that were clearly adapted to lure highly specialized insects. These fossils--an apparent cross section of angiosperm floral diversity from a time when major modern lineages were being established--can advance our understanding of the history of various floral organs and, with the help of an exciting new computer program created by Kevin Nixon, a colleague at Cornell University, the relationships of both extinct and living species.

The "primitive" flowers in these deposits share certain characteristics with several living species, the most familiar of which are the magnolia and the tulip tree: their spirally arranged floral parts are often unfused (see A, left), and their pollen grains are elongate, with a narrow furrow running down the middle (see C). The sediments also contain fossilized remains of weevils--beetles that may have pollinated these magnolia-like plants, wandering over them as they ate and gathered the exposed pollen, much as their living relatives do today.

[A and C ILLUSTRATION OMITTED]

Other fossil flowers are what we consider more advanced. Based on numerous characteristics--including a rosette of wedge-shaped stigmas (see D) and the perforated surface of its pollen (see B)--we have identified one of these plants as a close relative of species in the modern tropical genus Clusia. The fossils show that, like its modern relatives, this ancient plant appears to have offered its pollinators a highly evolved, more specialized reward than pollen or even nectar: resin.

[B and D ILLUSTRATION OMITTED]

Both Clusia and these fossils are dioecious--that is, they bear separate male and female flowers. In some Clusia species, the female flowers have modified anthers that open up to release resin rather than pollen. Stingless honeybees in the tribe Meliponini collect pollen from the male flowers and resin (for use in nest construction) from the females. Some of the Clusia-type fossils also show resinlike material stretching across the openings of modified anthers. And in nearby deposits of about the same age, entomologists David Grimaldi and Charles Michener have found stingless bees preserved in amber. Together, the two fossil discoveries provide compelling evidence that the close relationship between bees and flowers is an old one, dating back to the days of the dinosaurs.

Fossil flowers of other species found at this locality--including several distant relatives of the blueberry and rhododendron--support this view. Some of these flowers (see E) produced a mass of pollen grains connected by fine strands (see F) of the same material that made up the pollen walls. The only living plants that package their pollen this way--as a unit rather than as separate grains--are those that have evolved a close relationship with a very reliable pollinator, such as the bee that can be counted on to fly straight from one rhododendron flower to another without getting sidetracked along the way and delivering the valuable package to the wrong address.

Early Bloomers

Natural History, May, 1999 by William Crepet

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