230-million-year-old fossils push back date of resin-preserved arthropods
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ANCIENT MITESThe new mite species Triasacarus fedelei (top) and Ampezzoa triassica (bottom) were found in 230-million-year-old fossilized amber. The find pushes back the record of oldest arthropods in amber by about 100 million years.A. Schmidt/University of Göttingen
Mites could give competitors on Survivor a run for their game-show money.
Two of the tiny creatures, trapped in fossilized tree resin, smash the record for ancient amber-preserved arthropods, a group of critters that includes beetles, butterflies, spiders and shrimp. At 230 million years old, the mite fossils are about 100 million years older than previous finds, and suggest that mites’ basic body blueprint may be built to outwit, outplay and outlast.
“Dinosaurs have come and gone, but mites have hardly changed,” says David Grimaldi of the American Museum of Natural History in New York City. “Their body form is quite similar to what we see in gall mites today.”
RESIN FOSSILSFossilized amber droplets represent resin that oozed out of an ancient conifer tree and hardened, trapping tiny animals inside.S. Castelli/University of Padova
That similarity is somewhat surprising considering that the Earth was profoundly different 230 million years ago, when most plants were ferns, the Atlantic Ocean didn’t exist and pterosaurs cruised the skies. The Triassic-period mites, however, look just like their present-day relatives: They have segmented bodies, piercing mouthparts and legs bristling with “featherclaws,” Grimaldi and his colleagues report online August 27 in the Proceedings of the National Academy of Sciences.
Mites seem to have made major adaptations, however, to their food supply. Unlike modern gall mites, which feast mostly on flowering plants (sometimes forming bumpy growths on the leaves), the Triassic ones chowed on a more primitive type of greenery: conifers. Grimaldi’s team discovered the two new species of mites, one Triasacarus fedelei and the other Ampezzoa triassica, smothered in droplets of amber from a now-extinct species of cone-bearing tree. The amber also held the remnants of a fly.
The golden globules are about the size of a grain of rice. The creatures are visible only through a microscope as tiny flecks that mar the fossilized resin’s clarity. “You can see these little critters in all their lifelike glory — it’s really quite amazing,” says paleoentomologist Michael Engel of the University of Kansas in Lawrence.
Limestone and shale can also hold arthropod fossils, but amber allows researchers to take a more intimate look. “The detail preservation in these mites is leaps better than other Triassic arthropods,” Engel says. “Actually, leaps is an understatement. The difference in preservation is a massive chasm.”
The team picked through ancient sediments in the Dolomite Alps of northeastern Italy in search of resin dollops, then took two years to examine 70,000 amber droplets, shards and fragments. Only three housed arthropods. “With this discovery, we’re obviously all hot and ready to go back and screen through lots more,” Grimaldi says.
Arthropods are the most diverse group of creatures on Earth, making up more than 50 percent of all known species. They’re one of the key lineages of life, says Engel. “Anything we can do to better understand what led to their successes and failures can tell us how they shaped the planet in the past and how they’re shaping the planet today,” he says.