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Banner image: Abel Campos, majoring in Ecology & Evolutionary Biology, examines a fossil in the Invertebrate Paleontology department at the University of Colorado Museum of Natural History. (Photo:听Casey A. Cass / CU Boulder)听

Botanists and paleontologists, led by researchers from听CU Boulder, have identified a fossil chili pepper that may rewrite the geography and evolutionary timeline of the tomato plant family.听

The team鈥檚 findings, published last month in the journal , show that the chili pepper tribe (Capsiceae) within the tomato, or nightshade (Solanaceae), family is much older and was much more widespread than previously thought. Scientists previously believed that chili peppers evolved in South America at most 15 million years ago, but new research pushes that date to at least 50 million years ago鈥攁nd suggests that chili peppers were in fact present in North America at that time.听

Roc铆o Deanna, a postdoctoral researcher in ecology and evolutionary biology, and Abel Campos, an undergraduate double majoring in evolutionary biology and molecular, cellular and developmental biology, weren't planning to rewrite history when they met up one afternoon at the CU Boulder Museum of Natural History in 2021. Yet among a group of specimens in its collections gathered from the Green River Formation鈥攇eological treasure trove in northwestern Colorado and southwestern Wyoming鈥擠eanna spotted a specific, solanaceous trait embedded in one fossil: little spikes on the end of a fruiting stem.

鈥淎t first, I thought 鈥楴o way! This can鈥檛 be true,鈥欌�� said Deanna, lead author of the study. 鈥淏ut it was so characteristic of the chili pepper.鈥澨�

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 (DMNS). 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.听

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 of the Americas by as early as 50 million years ago.

鈥淭he family is way older than we thought,鈥� said Deanna, also a faculty member at the National University of Cordoba.

A fruit-fossil history听

The nightshade family comprises 3,000 species and almost 100 different genera, including chili peppers. The ancient chili pepper was technically a fruit鈥攁nd a berry, at that. While tomatoes and peppers are commonly associated with vegetables, they have seeds on the inside, which officially categorizes them as fruits.听

The researchers cannot be sure of the chili鈥檚 exact shape or color, but it was probably on the smaller end compared to modern day chili peppers. And like its relatives, it could have been quite spicy, according to Deanna.听

Deanna and Campos identified the fossil by the unique shape of its calyx teeth: spikes on the end of the fruiting stem that hold on to the pepper, like those which hold a gemstone in a ring.

鈥淭he world has maybe 300,000 plant species. The only plants with that kind of calyx is this group of 80 or 90 species,鈥� said Stacey Smith, senior author of the paper and associate professor of evolutionary biology at CU Boulder.

Paleontologists collected the CU Boulder fossil from the Green River Formation in the 1990s. But its exact identity remained a mystery for years, in part because there are only a handful of 鈥渟olanologists,鈥� botanists who study the nightshade family, in the world. When Deanna found these Colorado-based fossils, she had just returned from a global search for tomato family fossil specimens, only to find some 鈥渏ust ripe for the picking鈥� right on campus.听

鈥淎 lot of discoveries happen decades after the specimens have been collected,鈥� said Smith. 鈥淲ho knows how many other new fossil species are sitting in any of these museums? They're just waiting for the right eyes to look at them.鈥澨�

Trickle-down evolution

These chili pepper fossils were around during the Eocene, a geologic epoch that lasted from about 34 to 56 million years ago as the continents drifted toward their present positions. During this balmy time in Earth鈥檚 history, carbon dioxide levels ranged between 700 and 900 parts per million (twice as high as they are today), and palm trees grew as far north as Alaska. Because little to no ice was present on Earth, sea level was as much as 500 feet higher than it is today.听

Scientists had assumed that the origins of 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, which have since largely disappeared.

But how did these peppers first get to North America? It鈥檚 now a case of 鈥渢he chicken or the chili pepper?鈥�

Experts 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鈥攁nd 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.听

So the nightshade family could have easily started in North America instead of South America, then dispersed in the other direction鈥攁nd with this discovery, scientists can no longer say for sure, said Smith.听

鈥淭hese chili peppers, a species that we thought arose in an evolutionary blink of an eye, have been around for a super long time,鈥� said Smith. 鈥淲e're still coming to grips with this new timeline.鈥�

Additional authors on this publication include: Camila Mart铆nez, Universidad EAFIT and Smithsonian Tropical Research Institute; Steven Manchester, Florida Museum of Natural History, University of Florida; Peter Wilf, Pennsylvania State University; Sandra Knapp, Natural History Museum, London; Franco E. Chiarini, Gloria E. Barboza, and Gabriel Bernardello of the Instituto Multidisciplinario de Biologia Vegetal, IMBIV (CONICET-UNC); Herve Sauquet, National Herbarium of New South Wales and Evolution and Ecology Research Centre, University of New South Wales; Ellen Dean, Center for Plant Diversity, University of California; Andres Orejuela, Grupo de Investigacion en Recursos Naturales Amazonicos 鈥� GRAM, Facultad de Ingenier谋as y Ciencias Basicas, Instituto Tecnol ogico del Putumayo, and Subdireccion cient谋fica, Jard谋n Botanico de Bogota Jose Celestino Mutis.听