Botanists and paleontologists led by researchers at the University of Colorado Boulder have identified a fossil chili pepper that may rewrite the geography and evolutionary timeline of the tomato plant family.
The U.S. National Science Foundation-supported findings, published in the journal New Phytologist, show that the chili pepper tribe (Capsiceae) in the tomato, or nightshade (Solanaceae), family is much older and was much more widespread than previously thought. Scientists believed that chili peppers evolved in South America at most 15 million years ago, but the new research pushes that date to at least 50 million years ago - and suggests that chili peppers were in fact present in North America at that time.
Rocío Deanna and Abel Campos weren't planning to rewrite history when they met up one afternoon at the CU Boulder Museum of Natural History. Yet among a group of specimens in its collections gathered from the Green River Formation - a geological treasure trove in northwestern Colorado and southwestern Wyoming - Deanna spotted a specific, solanaceous trait embedded in one fossil: little spikes on the end of a fruiting stem.
After they discovered two of these fossils in the CU Boulder collections, Deanna and Campos, a co-author of the study, found one more from the chili pepper tribe in collections at the Denver Museum of Nature and Science. All three fossils are from the Green River Formation in Colorado: the CU specimens from Garfield County and the DMNS fossil from Rio Blanco County.
"This research nicely highlights the importance of natural history collections in calibrating the timeline of evolution, in this case, of an agriculturally important plant family," said Katharina Dittmar, a program director in NSF's Division of Environmental Biology.
These chili pepper fossils from the Eocene geological epoch (34 to 56 million years ago) match the timeline of another nightshade fossil found in the Esmeraldas Formation in Colombia, revealing that the family was already distributed across all the Americas by as early as 50 million years ago.
The nightshade family comprises 3,000 species and almost 100 different genera, including chili peppers. The ancient chili pepper was technically a fruit - and a berry. While tomatoes and peppers are commonly associated with vegetables, they have seeds on the inside, which officially categorizes them as fruits.
"The world has maybe 300,000 plant species," said Stacey Smith, senior author of the paper. "The only plant with that kind of calyx is this group of 80 or 90 species."
Scientists had assumed that chili peppers began in South America roughly 10 to 15 million years ago, where they then dispersed over land and water to the other continents. While Colorado today is home to very few native nightshades and no chili peppers, this new discovery hints that a plethora of plants from the tomato plant family may have existed in North America 40 to 50 million years ago and have since largely disappeared.
Scientists have theorized that fruit-eating birds, which existed as early as 60 million years ago, may have carried seeds and plants around the world with them in their guts, stuck to their feathers or in the mud on their feet. But these birds also had to be eating something to fuel their journeys - and fleshy berries, or peppers, make the perfect fuel. Birds may have distributed peppers from continent to continent, but peppers may also have been crucial to the success of those same birds.
"These chili peppers, a species that we thought arose in an evolutionary blink of an eye, have been around for a very long time," said Smith.
