Scientists have described a new beetle species that lived over 65 million years ago--not based on its fossilized skeleton, but on the distinctive chew marks the beetles left while they munched on the leaves of a ginger plant. The findings, published in the 14 July issue of Science, help push back the time when a group of beetles called leaf beetles evolved their great diversity and demonstrate just how faithful some species can be to their favorite foods.
Cephaloleichnites strongi, as the new species has been dubbed, represents the earliest known rolled-leaf beetle species, hundreds of which still exist today. They are picky eaters, each species preferring just one of the ginger- and heliconia-like plants in the Zingiberales order. For decades, ecology students have learned about this impressive array of beetle-plant pairings, in which different rolled-leaf species adopt the same lifestyle but on their own distinct host plant. As ecologist Donald Strong--the beetle's namesake--showed in the 1970's, each beetle species leaves a unique chew mark on the plant's leaves.
Paleobotanist Peter Wilf of the University of Michigan, Ann Arbor, came across Strong's research in 1998, when he was studying a different sort of insect damage--mysterious specks of fossilized material found on 53-million-year-old fossil leaves from Wyoming. When he and his colleague Conrad Labandeira, a paleobiologist at the Smithsonian Institution's National Museum of Natural History, took a second look at the leaves, "we realized the damage [seen by Strong in the modern leaves] matched beautifully with what we had," Labandeira recalls. Moreover, the fossil leaves looked very much like some modern gingers.
Later, Labandeira also discovered the same signature chew marks on ginger leave fossils in the collection of Kirk Johnson at the Denver Museum of Natural History. Because these fossils came from a North Dakota deposit dating back to the Late Cretaceous, "we now know this insect is 20 million years older than if we just looked at body fossils," Wilf points out.
The findings lend support to a theory proposed by Harvard insect evolutionist Brian D. Farrell, who thinks most plant-eating beetles likely evolved in parallel to flowering plants and therefore were quite diverse during the dinosaur's heyday (Science, 24 July 1998, p. 555). Until now, there has been little supporting fossil evidence, as only one relevant beetle fossil exists from that time. Now researchers may be able to get around this lack of fossils by looking at insect damage instead, says Leo Hickey, a paleobotanist at Yale University: "The work shows the potential of an overlooked resource in [studying] the evolution of insects."
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