Return with us now to the Jurassic Period when dinosaurs stomped through the lush foliage of the swampy countryside. Giant ferns and primitive palms are the order of the day, their large, broad leaves providing shade and decorating the landscape. Stately conifers grow in some areas. It is all very green, unbroken even by the muted colors of flowers - flowering plants haven't been invented yet.
Wait! How do we know this is what it looked like? Certainly, no one was around to take pictures, or even make cave paintings. How can we know what it might have been?All we have to go by is the fossil record of these ancient plants preserved in stone - nature's scrapbook, as it were. Unfortunately, nature was an imprecise scrapbook keeper, and there are gaps and holes in the stony record. It is left to today's paleobotanists (people who study fossil plants) to try and sort it all out.
"It's like being a detective," says William D. Tidwell, professor of botany at Brigham Young University and author of a guidebook to plant fossils, who has spent the past 38 years or so prodding, picking at and trying to decipher the stony code. "We have a black lake of ignorance, and we work in the bits of light along the edge."
Right now Tidwell is shining the light on what is affectionately known among rockhounds and botanists as "hermie wood." With no other common name, Hermanophyton is a plant that flourished 150 million or so years ago. It has a stem, with wedge-shaped sections grouped around a central core. It is different from most known living plants, says Tidwell, and information about it can only be pieced together from samples of petrified wood gathered from around the world.
The samples Tidwell pulls out came from the Morrison Formation of southern Utah and southwestern Colorado, but he's also collected and received pieces from collectors as far away as Australia. "I only hope I look that good 150 million years from now," he says, showing off the glossy perfection of some of his samples. He points out the pithy center and the grouping of stems, now a pretty, polished black. "All we have are the trunks; we haven't found any leaves yet."
Still, from his study, he has come up with a pretty good idea of what Hermanophyton looked like. It was probably a short to tall tree (some were more than 50 feet high), narrow-stemmed and crowned with leaves that dropped off as the plant grew, leaving numerous small leaf scars on the lower parts of the stem.
Was it food for the dinosaurs? Maybe. "All we know for sure is that dinosaurs ate each other. We know some ate plants, but some were like maggots on the landscape eating the beautiful plants before they could be preserved."
The mystery is part of the compulsion to learn more, he says. "It is interesting to learn more about what it was like back then. It's a part of our history, part of our life."
The plant fossil record of western North America and Canada stretches back 500 million years, detailing not only types and species of plants that once grew here but showing dramatic climatic shifts and continental movement.
But it is a very incomplete record. Fossils that have been found represent only a small number of the plants that have lived on the planet. Most plants decay after they die, turning into chemicals and nutrients that replenish the soil. Only those lucky enough to have been buried in a lake or swamp, or been covered by volcanic ash, or subjected to one of the few other natural processes that allowed preservation, have survived in anything like the original form.
Perhaps it is that rarity or that connection with the past, but plant fossils have long fascinated both academic and amateur collectors alike. "You go to any rock show," says Tidwell, "and probably 50 percent of the collectors have fossil plants. And, he says, paleobotanists get a lot of help from these collectors. "They send in samples and want to know what they are." Many of his hermie wood pieces have come in that way.
So it was partly for these collectors that Tidwell wrote his guidebook, "Common Fossil Plants of North America," published by BYU press in 1975. "We wanted a guidebook with lots of pictures to help students and amateur collectors identify what they find. I went to rock shows in the '70s, and people had cases filled with petrified wood, but most was not even labeled."
The book was very popular and still is, even though it has been out of print for a number of years. "You rarely find a copy in a used bookstore," says Tidwell. And some people have gone to great lengths to get a book. "One man kept calling and calling because he wanted a copy. Then one day he called to say he finally had his book. The guy down the street had died and willed his copy to him."
Tidwell is happy to say that a new version of the book, updated and revised, is coming out this spring, published by the Smithsonian Institution Press. Illustrated with more than 800 drawings and photographs, it is designed to be a hands-on guide to help amateur collectors "identify and assess the significance of their finds." Introductory chapters talk about types of plant preservation and outline the development of such plant groups as ferns, fern allies and seed plants such as cycads, ginkgos, conifers and flowering plants. Also included is a table of more than 100 localities from northern New Mexico to British Columbia and from California to South Dakota where plant fossils have been commonly found.
If you want to study fossils, says Tidwell, all you really need is a natural curiosity. "Our wish to understand why things are as we find them and how they relate to each other probably has contributed more to the growth of science than all other influences combined."
Take, for example, Tidwell's colleague George Munzing, a man who has been collecting and studying fossils for years and often comes to use the facilities and aid in the research at BYU. He found his first fossil when he was 13. "I found that first beautiful piece and I wanted to know more - where it came from, how it formed. Look at me now."
Munzing has been particularly intrigued by opal woods, petrified wood where the organic wood has been filled with precious opal, and is currently writing a scientific paper on the mineralizing forces that petrified these woods. It is a process, he says, not of replacement but of preservation. "A lot of people think that the organic molecules of the wood were slowly replaced by inorganic molecules," but Munzing says that's not the case. "For one thing, inorganic molecules are smaller than the organic molecules they are supposed to replace. And for another, there is no evidence that inorganic molecules are able to react chemically in any way with the lignin and cellulose of the wood." So, he says, other processes are at work.
"Over the years, much of my research has been due to the finds and donations of rock-hounds around the world," says Tidwell. That's the thing about fossils. "The humblest collector has as good a chance of finding a beautiful, unique specimen as does the most learned professional."
Of course, in his lab Tidwell is able to do a lot of things that the average rockhound can't. When he receives a sample of petrified wood, for example, one of the first things he does is slice off a very thin section that can be viewed under the microscope. Cell structure, shape and color can all help to identify the species. He can analyze growth rings to study climate patterns. He can tell if this is a common find or a new species that has not been described before.
There are, he says, so many things that can be learned from these old, old stones. "Mostly, what we find are new questions."
And so the detective work continues. We may never know what plants the dinosaurs ate or exactly what the world looked like millions and millions of years ago. But ever so slowly William Tidwell and other paleobotanists around the world are filling in the blanks of the scrapbook.