By: Louisa Boswell
Most people enjoy plants at least to some extent, whether through tending a garden, hiking through the woods, or watering a couple of houseplants. But how many of us know how plants evolved to function like they do?
When you hear of a “paleobotanist”, it may not be clear what the title entails, or you might just call to mind Laura Dern’s character in Jurassic Park. In reality, paleobotanists, such as UNC-Chapel Hill’s Dr. Patricia Gensel, use plant fossils to investigate the evolution of plants and the relationships between fossils, modern plants, and current plant species.
You may have heard of Cooksonia, a transitional fossil showing the development of vascular tissue. However, it’s not easy for most to immediately understand the significance of it or other plant fossils. Dr. Gensel describes her field, explaining: “What we really want to do is characterize what plants existed at what moment in time, look for when certain plant structures appeared, and then also…understand something about their relationships to each other and to living ones”. She carefully studies the fossils that she collects, taking great care and pride in her work, to determine their nature and relationships to other fossils and living plants.
Paleobotanists use a variety of techniques in their work--some sophisticated, others less so. Fossils preserved in rock can be exposed by using acid to remove the rock, or the rock can be removed through slow, steady chipping by a sewing needle. All that is left behind are pieces of the plant that were tough enough to have survived. These fragment of stem or sporangia can be viewed under a microscope. Additionally, paleobotanists occasionally use a saw to slice a very thin section of the rock containing the fossil, which they can then examine under a microscope.
Not all parts of a plant are tough enough to be preserved, and sometimes all that the scientists have to work within a fossil is an imprint of the plant. Surprisingly enough, however, a lot of information can be gathered from an imprint. Everything from the size and general shape to specific structures on the plant may be visible imprints. Some fossils that have been discovered may be plant cells that have been filled with an unknown substance. In these cases, one can get a great look at the structure of the cell because the original cell wall is there, it is just filled with mineral, rather then being compressed and flattened in the rock.
Careful study of an area’s fossils can reveal a great deal of information about what types of plants grew in the area in the past. Paleobotanists can collect specimens from an area, classify and date them, and use that information to recreate the ecosystem that was in that area at a certain point in time. Dr. Gensel collects most of her fossils in Canada, mainly from the Devonian age (about 300-400 million years ago), because this period was an important one in plant evolution.
Dr. Gensel and her colleague, Dr. Andrews, write that “there was a progressive differentiation during the Devonian into specialized parts-stems, leaves, and roots-that served different functions. These were responses to problems of no small magnitude, and they were fundamental to all the diverse phases of plant evolution that took place in the Siluro-Devonian and thereafter”. These specialized plant parts were essential in the evolution from algae to land plants.
It is quite remarkable that we can still study a plant that lived hundreds of millions of years ago and compare it to current plants and other ancient fossilized plants to fill in the evolutionary record. Never before has it been so easy to learn about the past, and our understanding will continue to grow as long as paleobotanists like Dr. Gensel continue their research.
Dr. Gensel expresses that she loves her job, saying “I just need to know a lot of different things and that to me is nicely challenging. And then on top of that, I work with some of the earliest land plants that don’t look anything like those that live today so that adds another challenge, so all of it kind of combines to keep me very interested even now, and I’ve been doing it for a long time.” The most important thing for a scientist is to stay interested and stay curious so that, through their work, they can continue to increase our knowledge about this world.