Department of Biology

A new study co-led by researchers in the U.S. and China has pushed back the first-known physical evidence of insect flower pollination to 99 million years ago, during the mid-Cretaceous period.

The revelation is based upon a tumbling flower beetle with pollen on its legs discovered preserved in amber deep inside a mine in northern Myanmar. The fossil comes from the same amber deposit as the first ammonite discovered in amber, which was reported by the same research group earlier this year.

The newly reported fossil is described Nov. 11 in the journal of the Proceedings of the National Academy of Sciences. The fossil, which contains both the beetle and pollen grains, pushes back the earliest documented instance of insect pollination to a time when pterodactyls still roamed the skies -- or about 50 million years earlier than previously thought.

The co-lead author on the study is Bo Wang, an amber fossil expert at the Nanjing Institute of Geology and Palaeontology, where the specimen was procured and analyzed.

According to Dilcher, who provided a morphological review of the 62 grains of pollen in the amber, the shape and structure of the pollen shows it evolved to spread through contact with insects. These features include the pollen's size, "ornamentation" and clumping ability.

The grains also likely originated from a flower species in the group eudicots, one of the most common types of flowering plant species, he said.

The pollen was not easy to find. The powdery substance was revealed hidden in the insect's body hairs under a confocal laser microscopy. The analysis took advantage of the fact that pollen grains glow under fluorescent light, contrasting strongly with the darkness of the insect's shell.

*David Dilcher is also Professor Emeritus of Biology.