Drilling cores from Switzerland have revealed the oldest known fossils of the direct ancestors of flowering plants.

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The discovery of "beautifully preserved" 240-million-year-old pollen grains are evidence that flowering plants evolved 100 million years earlier than previously thought. Although it's hard to imagine the world without them, flowering plants evolved much later than some plant species around today.

Flowering plants evolved from now-extinct plant relatives of conifers, ginkgos, cycads, and seed ferns. The oldest known fossils from flowering plants are pollen grains. These grains are small, robust and numerous and therefore fossilize more easily than leaves and flowers.

An uninterrupted sequence of fossilized pollen from flowers begins in the Early Cretaceous, approximately 140 million years ago, and it had been assumed that flowering plants first evolved around that time. However, thanks to the work of scientists from the University of Zürich, flowering plant-like pollen has been discovered which predates this by many millions of years, implying that flowering plants may have originated in the Early Triassic (between 252 to 247 million years ago) or even earlier.

Many studies have tried to estimate the age of flowering plants from molecular data, but so far no consensus has been reached. Depending on dataset and method, these estimates range from the Triassic to the Cretaceous.

Peter Hochuli and Susanne Feist-Burkhardt from the University of Zürich studied two drilling cores from Weiach and Leuggern, northern Switzerland, and found pollen grains that resemble fossil pollen from the earliest known flowering plants. Using a laser microscope, they identified six different types of pollen.

In a previous study from 2004, Hochuli and Feist-Burkhardt documented different, but clearly related flowering-plant-like pollen from the Middle Triassic in cores from the Barents Sea, south of Spitsbergen. The samples from the present study were found 3000 km south of the previous site. The authors believe that even highly cautious scientists will now be convinced that flowering plants evolved long before the Cretaceous.

In the Middle Triassic, both the Barents Sea and Switzerland lay in the subtropics, but the area of Switzerland was much drier than the region of the Barents Sea. This implies that these plants occurred across a broad ecological range.

Interestingly, pollen's structure suggests that the plants were pollinated by insects, most likely beetles, as bees would not evolve for another 100 million years.