Biting beetle gives away secrets

By BBC News Online's Jonathan Amos

Scientists have described a species of beetle that lived at least 66 million years ago, even though they have no fossil of the creature's body.

The only record they have of the minibeast are the marks it left as it chomped its way through its favourite food, ancient ginger leaves.

These traces in the leaves are as diagnostic of a beetle as tyres marks on a highway are of a skidding car

Dr Peter Wilf

Dr Peter Wilf, of the University of Michigan, and colleagues, studied 11 fossilised leaves unearthed in North Dakota and Wyoming.

Each had the characteristic chew marks that on some modern ginger plants and heliconias are left only by what are referred to as rolled-leaf hispine beetles.

Paleobotanist Dr Wilf told BBC News Online: "People ask how we can claim a beetle did the damage when we don't have its fossil. But these traces in the leaves are as diagnostic of a beetle as tyres marks on a highway are of a skidding car. There's just no doubt about it."

Size and shape

The larvae of hispines will eat out the tissue of young, curled up leaves, producing distinctive, long strips of damage that run parallel to the leaf veins.

Drs Wilf (right) and Labandeira collect plant fossils from the Great Divide Basin of southwestern Wyoming

The relationship between rolled-leaf hispine beetles and gingers, and their close relatives heliconias, has been well studied - most notably by Donald Strong Jr, a University of California-Davis researcher who first showed how to identify the beetles simply by the damage they did to leaves.

He found that the style of chew marks varied according to the size and shape of a particular beetle's jaws.

And it is to honour his work that Wilf's team, who report their work in the journal Science, have called their beetle Cephaloleichnites strongi.

Dr Wilf's group say the oldest bite marks they have come across date back 66 million years, to the Mesozoic. This is about 20 million years older than any body fossils so far found - even for the slightly wider group of hispines that includes the specific creatures thought responsible for the leaf damage documented in the Science paper.

Available and valuable

The researchers believe the fossilised bite marks may be vital in shedding light on the evolutionary relationship between beetles and flowering plants.

An adult rolled-leaf hispine beetle eats a leaf of Pleiostachya pruinosa

One theory has it that as flowering plants evolved many new species in the late Cretaceous so many new beetles evolved to fill in the ecological niches that suddenly became available.

"The suggestion is that the reason we have hundreds of thousands of beetles today has everything to do with the fact that we have hundreds of thousands of species of flowering plants, " Dr Wilf said.

With so few body fossils to study, the researchers say that the best way to test this theory is to look at the damage the insects left on the plants instead.

"The damage can provide valuable data that otherwise would be unavailable if one depended only on the body-fossil record of insects," said co-author Dr Conrad Labandeira, a paleobiologist at the Smithsonian Institution's National Museum of Natural History, in Washington DC.