January 29, 1998 -- A team of researchers from the American Museum of Natural History announced today in the journal Nature the discovery of the oldest fossil ants ever found. The extremely rare 92-million-year-old ants are preserved in amber from a location in New Jersey that has produced some of the world's most important amber-encased fossils. The new specimens are 50 million years older than the most ancient fossils that were clearly recognized as ants; the find thus proves unequivocally the existence of ants back into the Age of the Dinosaurs. The new specimens have important implications for understanding both the origin of ants and their rise to a position of ecological dominance in the world today.
The new ant specimens are of particular consequence because they show the presence of a "metapleural gland," which is the distinguishing anatomical feature of ants and is a key to their ability to live in colonies underground or in rotting trees. This gland, found above the hind legs, secretes a substance that functions as an antibiotic and prevents bacteria and fungi from invading the ants' nests and infecting the members of the colony. The development of this gland is believed to be associated with the evolution of the ants' social system, which has been a key factor in their tremendous ecological dominance. Ants are so successful that they represent up to 25% of the total animal biomass in Amazonia; even in New York City's Central Park they are, by weight, the most common creature.
The new specimens comprise three worker and four male ants. One of the workers is a complete, well-preserved specimen from the group known as Sphecomyrma freyi, a primitive kind of ant. This insect was first described in 1967 by renowned entomologist E.O. Wilson and his colleagues, but because no metapleural gland was clearly visible, it was uncertain at that time whether it was truly an ant. The new fossil ant in amber resolves the debate over the identity of this ancient insect. Of the remaining fossil ants, two of the males are a new species of Baikuris (which previously had only been found in Siberian amber), a third male is from an undetermined genus, and the fourth male may be a Sphecomyrma freyi and would therefore be the first known male of this group. The two other workers represent a new genus that is much more advanced than Sphecomyrma, and is related to a group of ants, the subfamily Ponerinae, that are widely distributed in tropical and subtropical areas today. (Most of these ants today are known for their powerful stings.) The discovery of both primitive and more advanced fossil ants in 92-million-year-old amber shows that the major lineages of ants arose before the great extinction at the end of the Cretaceous, 65 million years ago. A reasonable estimate would place the origin of ants in the Lower Cretaceous at about 130 million years ago.
Ant fossils from the Cretaceous Period are extremely rare, but those from the subsequent Tertiary are quite abundant, indicating that the great radiation of ants did not begin until the close of the Cretaceous -- a time that also marked the end of the Age of the Dinosaurs. The tantalizing question of what, in addition to their sociality, led to the unparalleled success of ants after this Period is still open.
The authors of the Nature paper are: Donat Agosti, research scientist; David A. Grimaldi, chairman and curator; and James Carpenter, curator, all of the American Museum of Natural History's Department of Entomology. Funding for the research was provided by American Museum of Natural History Trustee Henry G. Walter and by Henry and Meryl Silverstein.
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