The ancient mites likely fed on the leaves of the tree that ultimately preserved them, a conifer in the extinct family Cheirolepidiaceae. The mites are so old that they pre-date the existence of flowering plants.
"We now know that gall mites are very adaptable," Grimaldi said. "When flowering plants entered the scene, these mites shifted their feeding habits, and today, only 3 percent of the species live on conifers. This shows how gall mites tracked plants in time and evolved with their hosts."
As for the fly, the researchers aren't sure what kind it was. The amber pieces are very small, so when the invertebrates kicked the bucket by drowning in tree resin, they were entombed in mere drops of the stuff.
"Amber is an extremely valuable tool for paleontologists because it preserves specimens with microscopic fidelity, allowing uniquely accurate estimates of the amount of evolutionary change over millions of years," Grimaldi, who is a world authority on amber and fossil arthropods, said.
He and his colleagues hope to find more Triassic Era amber inclusions.