Archive for August 28th, 2012

230-million-year-old mites found in Dolomite amber

Tuesday, August 28th, 2012

Scientists have found two gall mites and a fly preserved in 230-million-year-old Late Triassic amber from the Dolomite Alps in northeastern Italy. These are the first arthropods (a phylum of invertebrates including insects, arachnids and crustaceans) found in amber from the Triassic. Although arthropods appear in the fossil record starting in the Early Cambrian period around 540 million years ago, these are the oldest arthropods ever discovered trapped in amber, 100 million years older than prior examples.

Amber droplets found in Triassic outcrops of the Dolomite AlpsResearchers gathered thousands of droplets of amber no more than six millimeters long from outcrops on the Dolomites, then spent two years screening each tiny piece for any plant or creature they might contain. If you think this must have been a painfully tedious experience, you think right.

“Before preparation, one of the tiny flecks of amber, about 1 millimeter in diameter, wafted onto the floor of my lab,” [David Grimaldi, curator of invertebrate zoology at the American Museum of Natural History in New York,] recalled. “Alex Schmidt and my assistant who did the prep, Paul Nascimbene, spent about three hours on their hands and knees with flashlights. I don’t know how, but they found the speck on the floor hidden in the corner between two lab benches. It was a nerve-wracking time.”

Triassic midge fly parts, head upper leftIt’s a good thing they were that dedicated to the task, because out of the 70,000 droplets of amber they analyzed for inclusions, three of them contained the groundbreaking arthropods: one partial midge fly (Diptera) about the size of a head of a pin, and two new species of gall mites. The amber had preserved the head, antenna, four legs and some fragments of the body of the midge fly which taken together were 1.5-2 millimeters in size.

The mites were complete and far tinier. One of them, Triasacarus fedelei, is shaped like a worm and is 210 microns long. Due to its body shape and differences in the structure of the mouth, researchers believe it may be an ancestor of modern gall mites. The second mite, Ampezzoa triassica, is even smaller at 124 microns in length. Its shape is more typical of modern gall mites.

Gall mites in 230-million-year-old amber dropletsThe amber preserved these creatures so well that scientists could examine them in microscopic detail, allowing them to identify minute characteristics like tiny waxy filaments on the surface of Triasacarus fedelei’s body that are thought to have helped protect them from predators, parasites and the elements. Both mites have two pairs of legs like present-day mites.

One way in which they’re different from their modern relatives is that the Triassic mites must have fed on conifers, since it’s conifer resin that hardens into amber. Today 97% of Eriophyoidea, the group gall mites belong to, feed on flowering plants, which means the mites changed their eating and living habits entirely when the new plant species came on the scene about 140 million years ago.

The Dolomite amber study has been published in the current issue of the Proceedings of the National Academy of Sciences. You can read it here if you have access to a subscription.

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