ANATOMY OF A ROSE -- EXPLORING THE SECRET LIFE OF FLOWERS
TWELVE: Flowers and Dinosaurs
IT'S A BILLION YEARS AGO.
You are in the water and everything is easy and everything is right there, in the water, floating by. You release your male reproductive cells and they swim away. You release your female reproductive cells and they swim away. You leave the ocean. You come to a freshwater lake. It's nice here, too. You are as happy as the clam that hasn't evolved yet.
You're not vain. You don't think of yourself as the Eve of green plants. You're the size of a pinhead, one cell thick. You have this problem. The shoreline of the lake keeps changing. The water leaves and you dry up.
You adapt. You protect yourself from the sun. When the water rises, you send out sperm. When the water recedes, you sit there adapting. It's a new you. A new look. You no longer think of yourself as a green alga.
You like the word moss.
It's 500 million years ago.
You have no leaves. You have no stems. You have no roots. You have trouble transporting minerals and water. You decide to become a fern. Someday you will be a houseplant. Human slaves will mist you everyday. You will live in a big house with a view of the ocean.
You're a little vain now. You're intrigued by packaging. You'd like to protect your embryo. You call it a seed. You'd like to put your sperm cells in a container. You call it pollen.
It's 200 million years ago.
You have discovered aerodynamics. The wind takes your sperm to another plant, and by now you are a pine tree, a member of the biggest gang in town. You roll across the land undulating in huge forests. You are the most successful form of vegetation on earth. If you could find one your size, you'd wear a red and black jacket emblazoned with your team name: The Gymnosperms.
You are a gymnosperm. You don't have flowers or fruit. You are resting on your laurels, which also haven't evolved yet. You feel immensely proud.
You want to share your feelings. You look around the forest. You notice the dinosaurs.
TWO HUNDRED MILLION YEARS AGO, at the beginning of the Jurassic period, gymnosperms and reptiles dominate plant and animal life on land. The group of reptiles known as dinosaurs has been around for a long time. In the next 60 million years, they will get bigger and bigger. Eventually some will be seventy-five feet long and weigh seventy tons. They roam in herds and walk on pillar-like legs. Their movements shake the ground. Under a hot sun, they browse the tops of coniferous trees, cycads, ginkgoes, and seed ferns, drawing leafy branches through their rakelike teeth and processing food slowly in their stomachs. At this time, most of the continents still huddle together in one big land mass. A few bees and other insects flit through the air. A few ratlike mammals scurry in the dirt.
The writer Loren Eiseley has described the scene: "Inland the monotonous green of the pine and spruce forests with their primitive cone flowers stretched everywhere. No grass hindered the fall of the naked seeds to earth. Great sequoias towered to the skies. The world of that time has a certain appeal but it is a giant's world, a world moving slowly like the reptiles who stalked magnificently among the boles of the trees."
In this monotonous green world, real flowers are starting to evolve, perhaps from seed ferns (a group of plants extinct today), perhaps from the shrubby bennettites (also extinct), or perhaps from plants whose descendants include members in the genus Ephedra.
Meanwhile the huge land mass is breaking apart. India rafts north. North America drifts west. By 140 million years ago, toward the end of the Jurassic period, the ovules of some plants may be beginning to develop fleshy carpels that enclose and protect their previously naked seeds. The seeds of these plants spread and catch a ride on the drifting continents.
Across the seafloor, the passage of North America is triggering tremendous volcanic activity. Mountain ranges rise. Africa and South America separate. The shallow seas of Europe start to drain away.
Too much is happening. There is too much time.
This is why we like fossils. A fossil is limited to the life of a single plant or animal at a specific moment. I can see myself in a fossil: smothered in silt, water squeezed from every cell, compressed, hardening, waiting for a scientist to find me. I can understand a single fate.
One of the earliest flower fossils is 120 million years old, from Koonwarra, Australia. Scientists first thought this plant was a no-count fern frond. Then someone noticed flower clusters the size of a period. The tiny florets are all female, without sepals, petals, or stamens. The single carpel has no style and is protected by reduced leaves. The entire fossil is 1-1/2 inch long and looks like a small, black pepper plant. Its male counterpart is presumably somewhere, buried in rock. Most likely, the Koonwarra flower was pollinated by the wind. Perhaps small insects were also involved.
At this time, during the early Cretaceous period, beetles are already pollinating cycads with their palmlike leaves. Other gymnosperms may be using pollinators as well. Certainly, bees and flies have been around as long as the dinosaurs.
Unaccountably, the dinosaurs are starting to shrink in size. Since smaller animals lose heat more rapidly, dinosaurs now need a higher metabolism. Herbivores begin to chew more efficiently. Nostrils get bigger and breathing also becomes more efficient. The breathing passages separate from the mouth cavity. Now dinosaurs can chew and breathe at the same time, quickly digesting food and transforming it into energy. The ratio of brain size to body weight increases. Behavior becomes more flexible.
By the late Cretaceous, dinosaurs have diversified to such an extent that there are more kinds of them, small to big, than at any other time.
Flowers are also diversifying. In Asia and North America, they are leaving fossil records that are 110 million years old. Some flowers have both male and female organs. Some have eight carpels, not just one. Some carpels have fused.
In New Jersey, 90 million years ago, a fire hardened the cell walls of hundreds of flowers trapped in muck. The muck turned to stone. These tiny blossoms are three-dimensional. There are plants here similar to magnolias with spirally arranged floral parts. There are the fossilized remains of weevils, suggesting that some flowers were pollinated in a typical "mess and soil" beetle style, with insects wandering over the plant, eating, mating, defecating, picking up pollen, and carrying pollen, just as beetles do today. There are flowers that packaged their pollen in a mass, something flowers do when they have a pollinator they trust. There are flowers related to modern-day rhododendrons, hydrangeas, carnations, azaleas, pitcher plants, and oaks. There are flowers that offered resin as a reward.
This is a bouquet from the Late Cretaceous.
Everywhere now, during the Late Cretaceous, on the drifting continents, flowering plants have established themselves as weedy herbs and shrubs, able to colonize open or disturbed areas. Flowers are developing bilateral symmetry. Petals are fusing into shapes that small creatures can crawl into. Insects are responding and changing. They discover a nectar gland. They flit from one sugary drink to the next. A moth swoops lazily past a dinosaur's nose. It lands on a pleasing, sweet-smelling blossom.
Dinosaurs, oddly, may have helped make this possible.
In the Jurassic period, the dominant herbivores were giant creatures that ate the tops of gymnosperms. Usually these large plants could survive this assault, while their seedlings and saplings matured below.
But later, during the Cretaceous period, the dominant herbivore became smaller and shorter, with a large, muscular head and flat, grinding teeth for chewing plant tissue. These herbivores may have eaten the lower, younger trees, perhaps before they could mature and seed. These dinosaurs interacted with gymnosperms in a very different way.
And gymnosperms, throughout the Cretaceous period, began to decline. Suddenly the fast-growing herb and shrub, the little angiosperm, the intrepid colonizer, had the advantage. As the great forests of gymnosperms died out, even more habitat opened up, new places for flowers to grow and evolve.
In Loren Eiseley's famous essay, "How Flowers Changed the World," written in 1972, flowering plants provided small mammals a new high-energy food source: nectar, pollen, seeds, and fruit. In concentrated form, these foods would allow mammals to expand and flourish. After the tiny flowers of grass appeared, there would be plains of grazers, all mammals now, and the quick rush of a furry predator. Millions of years later, at the transitional edge between plain and wood, a particularly curious mammal would stand upright, and stare, holding a stick.
Eiseley ended his essay with this memorable sentence: "The weight of a petal had changed the face of the world and made it ours."
We remember this sentence when we look at a weedy mustard, fading yellow, or a ragged poppy dusty on the roadside. Flowers may have prepared the way for you and me.
Dinosaurs may have prepared the way for flowers.
AT LEAST ONCE IN OUR LIVES, we have imagined ourselves in the world of dinosaurs. Specifically, we are hiding in the foliage, 65 million years ago, while Tyrannosaurus rex roars nearby.
Here she comes, closer and closer.
T rex is a dinosaur with a street name. T rex moves like a madwoman, jerky, purposeful, looking over her shoulder. She is forty-five feet long and nineteen feet high, and she weighs four tons. Mostly we imagine her jaws and teeth. We have atavistic memories, bolstered by TV. We remember what it was like to be eaten alive.
If we looked around, away from the teeth, we would see a familiar landscape. There are conifers like bald cypress, redwood, and cedar. There are also sycamores, laurels, tulip trees, and magnolia trees. We don't see grass yet, and we don't see anything like sunflowers. But we do see a lot of flowering plants. The Age of Gymnosperms is almost over.
Tyrannosaurus rex stomps out of sight, muttering in the tulip trees. She doesn't know that more than a third of all animal and plant species on earth and two-thirds on land are about to go extinct, that she lives at what paleontologists call the KT Boundary, the thin border of time between the end of the Cretaceous and the beginning of the Tertiary period. She doesn't know that when paleontologists talk about "what crossed over the KT," what survived, they do not mention her name.
NO ONE REALLY KNOWS what happened.
For many years, volcanoes had been erupting, violently and continuously. These eruptions might have injected poisons into the air. They might have caused global cooling. Meanwhile, shallow seas were withdrawing from the continents. Among the dinosaurs, there might have been disease and a dwindling gene pool. Dinosaurs might even have been bothered by those small, pesky, egg-eating mammals.
Certainly they were bothered, at the end of the Cretaceous, when an asteroid hit the earth. In the Yucatan Peninsula, the impact crater is 120 miles wide. The crash sprayed debris all over North America and threw comet-enriched material or iridium around the world. Large areas were devastated by fire. For months, everywhere, dust and ash probably obscured the sun, while chemicals caused global acidic rain.
In this scenario, dinosaurs died quickly. Smaller reptiles and mammals, feeding on dead and decaying plants, "crossed over." Certain seeds "crossed over."
In one site in North Dakota, 80 percent of plant species disappeared. This number is based on the fossilized plant parts seen below and above the KT Boundary, which is marked by iridium and shocked mineral grains, remnants of the asteroid crash. Just above the boundary, fern spores increase, and ferns may have been a post-impact recovery plant. For a short while, fern prairies may have dominated the landscape.
In another site, in the Russian Far East, only one angiosperm crossed the boundary.
Dinosaurs were gone. Flowers were devastated.
According to some people, you can set your watch by it. After a mass extinction, evolution speeds up. Everyone diversifies. Everyone radiates. Mass extinctions are usually caused by violent changes in habitat and climate. These same changes often mean that the populations of surviving species become isolated from each other. New species evolve. The world fills up again.
The next period of time, the Tertiary period, or Age of Mammals, is also the Age of Flowers. The surviving angiosperms set the standard. New, evolving flowers raise the bar. In an early pea blossom, we see wings and a keel. Members of the philodendron family have spathes and chambers for catching insects. The tubes and spurs of flowers lengthen to accommodate new kinds of insects and birds and bats. Suddenly there are butterflies!
Loren Eiseley writes, "Impressive as the slow-moving, dim-brained dinosaurs had been, it is doubtful if their age had supported anything like the diversity of life that now rioted across the planet or flashed in and out among the trees."
SCIENTISTS HAVE BEEN searching for the oldest living flower. They compared the mutation of genes in the chloroplasts of hundreds of plant species. When a computer program shuffled those genes into rough time order, an obscure shrub, Amborella, fell to the bottom.
Amborella is a living fossil, the closest relative of the first flowering plant. It has small, creamy flowers and red fruit and is found only on a single island in the South Pacific. Some botanists think that Amborella looks much like the original model, the first flower that had all the parts of a flower.
The next-oldest living blossom may be the water lily. Next comes the star-anise, and then the magnolia.
These flowers, and every flower in the world, are the descendants of those able to cross the KT Boundary. In turn, they trace back millions of years ago to that first green plant, the size of a pinhead, one cell thick, in a freshwater lake.
You are an angiosperm. You survived the Big Crash that you don't want to talk about. You discovered that there was more to life. You turned into an orchid. Now you amaze even yourself. You drip perfume. You pretend to be a wasp. You have secret corridors. You delight the bee.
Sometimes, dimly, you remember the dinosaurs.