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A wide variety of fruits and seeds that were smothered in the ash from a volcanic eruption nearly 75 million years ago suggest flowering plants were diverse and thriving in the time of the dinosaurs, far earlier than previously known.

Researchers had thought the emergence of large seeds and fruits followed the end-Cretaceous extinction, 66 million years ago, and was tied to the rise of mammals and birds.

“Now, we have evidence that large fruit and seeds and the related ecological conditions can be traced back to 10 million years before the asteroid impact that wiped out the dinosaurs,” says at the University of California, Berkeley.

Lee and his colleagues analysed ancient fossils collected from the Jose Creek Formation in New Mexico over the past three decades. They are so well preserved because, like the Roman city of Pompeii, the plant fossils were locked within a bed of ash from a volcanic eruption.

The team discovered an extraordinary 77 different kinds of fruits and seeds. Such a ready banquet of nutritious fruit would almost certainly have been eaten by herbivorous dinosaurs and other animals.

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The findings show flowering plants that enclose their seeds in fruit, also known as angiosperms, were co-evolving with the animals that fed on them as a way of dispersing their seeds.

“While many Mesozoic animals, like dinosaurs, birds, pterosaurs and mammals, were suggested to have consumed angiosperm diaspores, we didn’t have the botanical evidence supporting this,” says Lee. “Now we have.”

The first flowering plants emerge in the fossil record 136 million years ago, but, until now, it was thought early forms were mostly small and weedy and vastly different to the range of species that dominate Earth’s forests today.

In Cretaceous deposits elsewhere, the fruit and seeds are roughly the size of a poppy seed on average – far smaller than the blueberry-sized seeds at Jose Creek.

Of the 77 new types of seeds identified by the scientists, nearly a third are classified as fleshy while only 5 per cent are winged, which would imply dispersal by wind rather than animals.

Alongside the flowering plants, the tropical forest also contained several kinds of conifers, including a redwood relative, as well as palms.

While many of the seed shapes are familiar to us today, the forest structure would have been extremely different and unfamiliar, says team member , also at the University of California, Berkeley.

The larger fossils can be compared to blueberries and large acorns in size, she says. “We don’t have a good idea which plant group produced these; for that, you have to find them attached to shoots with leaves,” says Looy. “However, when they are fleshy they are likely dispersed by larger herbivores.”