Ants Were Already a Nuisance At Dinosaurs' Picnics
Fossil Specimen Dated to 92 Million Years Ago
By John Schwartz
The new find places the insects so far back in time that "we now know that ants were stinging dinosaurs," said famed entomologist E.O. Wilson of Harvard University.
In today's issue of the journal Nature, a team of entomologists from the American Museum of Natural History in New York describes two species of ants they discovered encased in amber dating back 92 million years. The discovery was made in Cliffwood Beach, N.J., at a site well known for containing insect fossils.
Each find is important, said David Grimaldi, head of the museum's department of entomology and a coauthor of the new report. The discovery of a fossilized specimen of a primitive, extinct ant species named Sphercomyrma freyi resolves a decades-old question about that insect: Is it an ant, or is it more like a wasp? Its head is wasplike; the waist is antlike; and the antennae are somewhere in between.
When the specimen was discovered in 1965, researchers suggested that it was not a true ant because it had so many features in common with the ant's winged ancestor. The entomologists could not find evidence in the tiny flattened fossils that the ants had the crucial metapleural gland, an organ found above the hind leg that produces antibiotic-like substances that keep the underground passages and trails from becoming choked with fungus and hazardous bacterial growth. Without that gland, the ants' famed social structure could never have developed. "It's really the defining feature of ants," Grimaldi said.
Thanks to the uncanny degree of preservation in the amber-encased ants, Grimaldi said, his team was able to prove that these insects did sport a metapleural gland. "Sphercomyrma is thus an ant," the authors wrote.
Wilson, a co-author of the paper on the initial discovery of Sphercomyrma, said work that he and others have done on the insect's anatomy, and the discovery that, like modern ants, they had the separate "castes" of queens and workers, had gone a long way toward proving the Sphercomyrma should be considered an ant. "Now the definitive identification of a metapleural gland clinches it," Wilson said.
The second discovery promises to be even more significant, Grimaldi said. The researchers also found a worker from a much more modern ant subfamily of the genus Ponerinae, whose members can still be found in the tropics today. Finding that such an advanced ant had scurried about approximately 90 million years ago could mean that the first primitive ants actually evolved many millions of years before. In the Nature papers, the authors suggested that true ants may have shown up on Earth 130 million years ago.
Until now, the oldest confirmed ant fossil specimens were from 42 million years ago.
Though the new research, led by Donat Agosti, puts the advent further back in time than ever before, the prehistoric critters were relatively rare until about 50 million years ago, when a vast ant population explosion began, according to the fossil record. Today, there are 14,000 described species and probably 6,000 more waiting to be discovered, Grimaldi said.
The timing of the ants' emergence might seem somewhat esoteric, but their story could open windows into understanding how many of Earth's creatures evolve and thrive. Despite opposable thumbs and personal computers, humans can scarcely claim to have done better than the ant, which emerged millions of years before humans, probably outweighs them in terms of sheer biomass and will certainly outlive them. Ants make up an estimated 25 percent of the total weight of animal life in the Amazonian rain forest.
Scientists are still trying to puzzle out the secret of the insects' ultimate success. It may have something to do with the cataclysmic occurrence 65 million years ago that killed the dinosaurs and many other species, and paved the way for mammalian dominance. It certainly has something to do with the ants' social structure. "A colony could beat an individual," Wilson said.
Grimaldi said he named the newly discovered Ponerine ant for William Brown, a mentor to both him and Wilson, and a co-author with Wilson of the paper based on the 1965 discovery.
Grimaldi sent a pre-publication version of the article to Brown, who thanked Grimaldi warmly for the honor; Brown died soon after. "It was really very poignant," Grimaldi said.
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