A few years ago, University of Maryland PhD student Nathan Jud was routinely examining a batch of ancient plant fossils in the Smithsonian Natural History Museum‘s collections when one in particular caught his eye.
“It looked sort of like a little piece of fern, so I tried to remove a bit of the rock that was covering it to get a sense of what type of fern it was,” he says. “But the more of the rock I would lift off the surface, the more fossil I found buried. What I thought had been one little piece of a leaf actually turned out to be two, connected to each other.”
As he labored to carefully flake the rock without defacing the fossil, he noticed a series of curious characteristics that suggested the preserved plant was no ordinary fern: It had a closed network of veins, rather than a series of branching ones that split off from each other without coming back together, and at its tips, there were tiny structures called glandular teeth, used to shed excess water.
“Eventually, I realized this wasn’t a fern at all, but some kind of early flowering plant,” he says. Its features wouldn’t be at all out of the ordinary in a plant growing outside today. The fact that they occur in a fossil from the Early Cretaceous period, though, is remarkable. At somewhere between 125 and 115 million years old, this fossil, described in a paper Jud published today in the American Journal of Botany, is among the oldest flowering plants ever found in North America.
Flowering plants—which replicate with sexual structures (i.e. flowers) to produce seeds—now dominate the planet, but for the first 300 million years or so of plant existence, beginning around 450 million years ago, the only types of vegetation belonged to older, more primitive families, such as algae, mosses and ferns, which all reproduce with spores rather than seeds, or gymnosperms, which produce seeds but not flowers.
During the Early Cretaceous, some of the first primitive flowering plants began to evolve. Researchers know that the layer in which this new fossil was found dates to this time period due to a few factors: Pollen analysis (which considers the chemical makeup of pollen embedded in the surrounding rock) and as well as study of the surrounding sediment itself. The same layer has previously produced several other flowering plant fossils of a similar age—together, they’re the oldest ever discovered in North America—but this is the oldest example of a eudicot, a group that includes roughly 70 percent of flowering plants worldwide today that share a distinctively-shaped pollen structure.
Compared to the other fossils found in the same layer, this one is especially remarkable for its derived traits, anatomical characteristics that were previously thought to have developed much more recently in flowers. Their existence so long ago suggests that some early plants were actually quite complex.
“When I compared it to living plants, I realized it was remarkably similar to the leaves of a certain group of modern poppies,” Jud says. “I didn’t expect to see a group that seemingly modern in a collection that old.” The fact that these features existed so long ago, both in this plant and other ancient fossils recently excavated in China, tells us that the evolution of flowering plants (which Charles Darwin famously called an “abominable mystery“) did not happen gradually, but instead occurred very rapidly during a narrow time interval in the Early Cretaceous period between when flowering plants first emerged and the date of this fossil.
There’s also a much more recent history of this fossil that’s just as fascinating. Jud did a bit of research and found that it’d been excavated in 1971 by a former Smithsonian curator, Leo Hickey, who went on to Yale and died in February before working with Jud to re-analyze the fossil after all these years. Hickey had found it during a dig at the Dutch Gap, in Virginia, in sediments that were exposed over a century earlier, by freed slaves who were forcibly taken from the Roanoke Island Freedmen’s Colony by Union troops and forced to dig a canal in August 1864.
While digging, they exposed ancient fossil-filled rocks, and a few decades later, in the 1870s and 1880s, scientists worked there to collect fossils and create some of the Smithsonian’s first fossil collections. Later, Hickey and other researchers returned to collect remaining specimens.
Jud honored this recent history in naming the ancient species that this specimen represents. “Potomac refers to the Potomac Group beds where the fossil was found, capnos is a reference to living poppies that are quite similar to the fossil and apeleutheron is the Greek word for freedmen,” he says. “So the new plant will be named Potomacapnos apeleutheron: roughly, ‘freedmen’s poppy of the Potomac.’”