Amber from 100-million-year-old deposits in Northern Spain has preserved and revealed the first ever record of insect pollination, scientists say.

Specimens of tiny insects covered with pollen grains in two pieces of Cretaceous era amber are the first record of pollen transport and social behavior in this group of animals, researchers said.

The amber featured inclusions of thysanopterans, also known as thrips, a group of tiny insects of less than 2 millimeters in length that feed on pollen and other plant tissue, they said.

One of the amber specimens was studied with synchrotron X-ray tomography at the European Synchrotron Radiation Facility in Grenoble, France, to reveal in three dimensions and at very high resolution the pollen grain distribution over the insect's body.

Researchers have determined the pollen is from a kind of cycad or ginkgo tree, a kind of living fossil of which only a few species are known to science, an ESRF release reported Tuesday.

"This is the oldest direct evidence for pollination, and the only one from the age of the dinosaurs," said Carmen Soriano, who led the investigation of the amber pieces with X-ray tomography at the ESRF.

"The co-evolution of flowering plants and insects, thanks to pollination, is a great evolutionary success story."