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CU Museum curator adjoint Gary Upchurch and colleagues find evidence in ‘botanical Pompeii’ that forests of tropical flowering plants thrived millions of years before dinosaurs’ extinction

In the Jose Creek Formation of south-central New Mexico near the town of Truth or Consequences is what researchers call a “botanical Pompeii.”��

There, preserved in volcanic ash, is fossil evidence that flowering plants became dominant in forests a lot earlier than previously thought—almost 10 million years earlier.

“There was a dogma that I helped create back in the ‘80s, which was that tropical-style rainforests, dominated by angiosperms (flowering plants), did not really get established until the Cenozoic (about 66 million years ago),” explains Gary Upchurch, CU Museum curator adjoint and former University of Colorado Boulder postdoctoral researcher. “There may have been some farther back in very isolated regions, but there is a big expansion of this type of vegetation in the early Cenozoic.

Gary Upchurch, CU Museum curator adjoint and former University of Colorado Boulder postdoctoral researcher, and his research colleagues found evidence that flowering plants formed rainforests 10 million years earlier than previously thought.

“So, I published papers on that back in the ‘80s, with the caveat that there may be some little bits here and there that are older.”

Over many years of research in the Jose Creek Formation, Upchurch and his colleagues discovered some of those “little bits”: diaspores, or the seeds and associated dispersal materials of flowering plants, dating back nearly 76 million years—almost 10 million years before an asteroid strike that led to the mass extinction of dinosaurs. They in the journal Science.

Previously, Upchurch explains, it was thought that flowering plants became dominant on the landscape�� ��only after this mass-extinction event, but the diaspores he and his colleagues unearthed in New Mexico say otherwise. They tell a story of angiosperms that developed large, fleshy fruits even before the rise of placental mammals and modern birds—which eat the fruit and help disperse the seeds—encouraged them to do so.��

An anomaly in the geologic record

“Flowering plants themselves are an anomaly in the geologic record because all the major phyla of plants occur in a very narrow window of time, basically by the Late Devonian [382 to 359 million years ago] into the Carboniferous [359 to 299 million years ago],” Upchurch says. “The flowering plant lineage must have been around then, but we don't see anything that we would call flowering plants until the Cretaceous [145 to 66 million years ago].

“There are some tantalizing remains that go back further in time, but the oldest that everybody would agree on is about 140 million years old. Now, flowering plants started off as weedy plants, perhaps in forest understories, and their seeds were small and dispersed mostly without help, maybe a little wind. One of the debates has been, when did they become big? When did they become dominant on the landscape?”

As a postdoctoral paleobotany researcher at 91��ý and longtime professor at Texas State University, from which he retired in 2020, Upchurch contributed to longstanding ideas in paleobotany and paleoecology that flowering plants thrived after the dinosaurs.

Throughout his research career, though, he has encountered evidence challenging those ideas. One of his earlier papers detailed an angiosperm leaf assemblage with rainforest structure in the Mid-Cretaceous Dakota Formation of Kansas that’s about 100 million years old.�� And recent papers by different authors describe Campanian-age tropical rainforests in northern Mexico and North Africa.

He also repeatedly encountered bias in the fossil record having to do with the fact that “so many of our fossil deposits are from coastlines and carbonaceous deposits,” he says. “And when you look today in places like the southeastern U.S., the swamps tend to be dominated by conifers, even though more broadly flowering plants are the dominants.”

Upchurch says he began researching in the Jose Creek Formation almost by accident. During his postdoctoral studies, one of his focuses was end-Cretaceous extinction and coming up with evidence for mass mortality of vegetation in response to the asteroid impact, followed by recovery.��

Around that time, noted geologist Greg Mack of New Mexico State University called Upchurch and said he had some fossils that he’d like somebody to look at.

“And whenever Greg Mack says that, you go, ‘Oh, my god, here’s my career,’” Upchurch says.

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Seed and fruit fossils found in the Jose Creek Formation of south-central New Mexico. (Image: Cindy Looy and Jaemin Lee/UC Berkeley)

So, beginning in 1991, Upchurch and later members of his lab began studying a series of locations that turned out to be Late Campanian Age, about 76 to 72.1 million years ago, and that were far inland from the epicontinental seaway that traversed North America during the Cretaceous.��

What they found was angiosperm dominance in at least some of the assemblages they studied, especially those that were developing not in swamps but in well-drained soils like those in the Jose Creek Formation.

Larger-than-expected fruit

To dig further into this dogma-busting evidence, Upchurch recruited students to join the research, one of whom was Dori Contreras, now director of paleontology and curator of paleobotany at the Perot Museum of Nature and Science in Dallas, Texas.

During her PhD studies at the University of California Berkeley, Contreras continued pursuing this research, working with her advisor, Cindy Looy. Analyzing the reproductive structures of the samples that Upchurch, Contreras and their research colleagues collected over the years, UC Berkeley PhD student Jaemin Lee found in the well-preserved specimens evidence of larger-than-expected fleshy fruit—about the size of a blueberry.

“One�� possible reason for this had to do with the fact that we were not dealing with fruits and seeds that got washed into the nearest pond,” Upchurch explains. “We were dealing with material that had basically been dropped from the parent plants into a volcanic ash bed that was preserving both the forest leaf litter and the diaspores. It’s a Pompeii type of situation.

“There’s a series of volcanic ash beds where we have radiometric dates as well as different types of fossil plant material—we have leaves, we have diaspores, we have exquisitely preserved petrified woods, both of conifers and angiosperms.”

Further, the diaspores they found suggest an ecological evolution toward humid and shady tropical forests rather than sunny, open environments and dispersal assistance by extinct mammals and birds, Upchurch says.

In ecology, he explains, organisms broadly reproduce via r-selection or K-selection. R-selection is all about numbers: disperse a huge number of small seeds and figure a tiny percentage will germinate and become established. K-selected species, on the other hand, have bigger diaspores and the focus is on survival and establishment because conditions might not be ideal—say, the shade of a tropical forest floor.��

Upchurch notes that while previously held ideas about angiosperms weren’t wrong—they did, in fact, abundantly flourish after the asteroid hit Earth—they were incomplete.

“As a scientist and a researcher, sometimes there have been moments I wasn’t expecting, these rare golden finds,” he says. “But the most important thing I’ve done is simply observe.”

Jaemin Lee, Dori L. Contreras, James G. Saulsbury and Cindy V. Looy contributed to this research.

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