A team of researchers
from the American Museum of Natural History announced recently
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. The new specimens are 50 million years older than
the most ancient fossils that were previously clearly recognized
as ants; the find thus proves 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.
