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.

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.

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“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.”

If caterpillars have munched through a lot of an oak tree’s leaves one year, then, the following spring, the tree’s buds open three days later. This delay means the caterpillars don’t have food available when they hatch, and so many die, halving how many leaves get eaten.

In spring, longer, warmer days drive trees to start growing again, opening buds and unfurling young leaves. Many species time their life cycle to match this, so some caterpillars, for example, hatch when the leaves are new and soft, so they can start eating immediately.

Now, at the University of Würzburg in Germany and his colleagues have discovered that oak trees have a way to fight back. They analysed the condition of tree canopies in images from radar satellites for a 2400-square-kilometre area in the northern Bavaria region of Germany between 2017 and 2021.

The forests there are dominated by two species of oak: the pedunculate or English oak (Quercus robur) and the sessile oak (Quercus petraea). Each pixel in the satellite images showed an area of 10 by 10 metres – about the size of the crown of one tree – and the team looked at 27,500 pixels in total.

In 2019, there was a massive outbreak of gypsy moths (Lymantria dispar), the hairy caterpillars of which feed on tree leaves, causing extensive damage when they are plentiful.

The satellite data showed which trees were stripped of leaves and how they responded. If an oak tree was heavily infested by caterpillars, the following spring, its leaves would emerge three days later than those of trees that hadn’t been badly eaten.

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This delay slashed the damage caused by feeding on the tree by 55 per cent compared with the year before. This is because the caterpillars still hatch at the same time, but they emerge to a bare cupboard rather than a feast of young leaves, leading many of them to die, says Mallick.

Oak trees also have other defences, including making leaves tougher to chew or that may attract other organisms to prey on the caterpillars. “The delay in bud opening seems to be more efficient than all these other defence mechanisms,” says Mallick, who thinks other deciduous plants may do it, too.

“It’s very plausible,” says at the University of Alberta in Canada, but he says the delay in bud emergence after the caterpillar outbreak is a correlation, and evidence of causality isn’t yet there. The delay could be caused by decreased plant vigour as a result of the leaf loss, he says, but having data from more than one outbreak would help work out what’s going on. “It certainly deserves more research.”

Mallick says the delay could be explained by physiological constraints such as resource depletion, but because it was seen across dozens of tree populations and was strongest in forests where a delay most effectively reduced herbivory, he thinks it isn’t just a physiological response by individual trees, but an adaptation.

“The mechanisms are intriguing and are a key aspect requiring further research,” says at the University of Eastern Finland.

Forests sometimes turn green later in spring than computer models predict they will based on temperatures, , and this study explains why, says Mallick.

“This point that plants respond to much more than climate change is very important,” says Cahill.