LAWRENCE — Dinosaurs likely munched on a lot more fruit than previously imagined.
Recent research appearing in the journal Science overturns a long-held idea that flowering plants didn't evolve large fruits and seeds until after the mass extinction of dinosaurs about 66 million years ago, when Earth was smacked by a giant asteroid.
Co-author James Saulsbury, postdoctoral researcher in the Biodiversity Institute and Natural History Museum at the University of Kansas, said the study changes how scientists think about plant-animal interactions and their role in plant evolution.
"This paper focuses on a fossil forest in New Mexico and the preserved fruits, seeds and other reproductive structures of the plants that lived there," he said. "These fossils change how we understand the way flowering plants became modern in terms of their reproductive ecology."
According to Saulsbury, paleobotanists generally had believed that flowering plants, which first appeared roughly 136 million years ago, only evolved modern reproductive strategies after the extinction event that wiped out the dinosaurs at the close of the Cretaceous.
"For much of their early history, they were relatively small, weedy plants that did not dominate forest canopies," Saulsbury said. "Although they gradually diversified and occupied more ecological niches, it was thought their seeds and dispersal structures remained small and were primarily dispersed by wind or without fleshy fruit."
The KU researcher said these early seeds and small fruits would have been similar in size to anything from dust particles to poppy seeds at their biggest. Modern flowering plants, by contrast, use a much wider variety of dispersal strategies. Many produce large, fleshy fruits that entice animals to spread their seeds. Think apples, pears, avocados, olives, and coconuts.
"The prevailing view has been that this more diverse reproductive ecology emerged only after the end-Cretaceous extinction," Saulsbury said. "Our study suggests that transition began much earlier. The largest fruits in our fossil flora are about the size of a grape. That may not sound especially large today, but it is remarkably large for flowering plants of that period."
The findings were drawn from an important field site near Truth or Consequences, New Mexico, where the study's authors, including Saulsbury, performed fieldwork over many years.
"The New Mexico fossil site is exceptional," he said. "My co-authors have referred to it as a 'botanical Pompeii' because of its remarkable preservation. The site contains a layer of volcanic ash preserved as rock, known as tuff, that stretches for more than a kilometer. The deposits formed at essentially the same time, preserving many plants where they lived and died. It provides a snapshot of a forest from about 74 million years ago and even preserves aspects of its spatial arrangement."
The site is also special because of the diversity and size of its fossil fruits and seeds, according to Saulsbury.
"However, we don't believe these findings are simply the result of preservation bias," he said. "It appears to represent a genuinely unusual forest."
According to Saulsbury, fruit size matters because size is associated with so many aspects of forest ecology.
"Large fruits tend to occur in moist environments with densely packed forests," he said. "Our findings indicate that modern-looking forest structure and reproductive ecology were developing earlier than previously believed. The diversification of flowering plant reproductive strategies did not have to wait until after the end-of-Cretaceous extinction."
The new research challenges one longstanding idea that large fruits evolved alongside the rapid diversification of mammals only after the asteroid impact eliminated the dinosaurs.
"As mammals expanded into newly available ecological niches, flowering plants were thought to have diversified their seed dispersal strategies in response," the KU researcher said. "Our findings suggest that story began earlier. If diverse, large fruits already existed in Cretaceous forests, they were likely being dispersed not only by early mammals but also by large dinosaurs and other animals."
Saulsbury participated in fieldwork, collected fossils and carried out much of the initial classification, measurement and analysis of the fossils.
"We sorted hundreds of fossil seeds into what we call morphotypes," he said. "These are groupings based on form rather than confirmed species because it is often impossible to determine whether similar-looking fossils represent one species or several."
Saulsbury's co-authors were lead author Jaemin Lee of the University of California, Berkeley; Dori Contreras of the Perot Museum of Nature and Science; Garland Upchurch of the University of Colorado Museum of Natural History and Cindy Looy of the University of California, Berkeley.
