The new species, Titanomyrma lubei, is related to giant ants previously found in German fossils. These long-distance relatives bolster the notion that the climate of the time had hot blips that allowed warmth-loving giant insects to spread from continent to continent, Archibald and a U.S.-Canada team propose online May 4 in the Proceedings of the Royal Society B.
An ancient ant wing from Tennessee had hinted that big ants lived in North America during this time, says Torsten Wappler of the University of Bonn in Germany. “But complete preserved specimens were not known until Bruce came up with this beautiful preserved fossil.”
The new fossil caught Archibald’s eye as he and co-author Kirk Johnson poked around storage drawers at the Denver Museum of Nature & Science, where Johnson works. The spookiest thing about the Wyoming ant may be that even at 5.1 centimeters [2 inches] long, she is not the largest ant ever found. A German specimen is slightly longer, as are queens of a living African driver ant, Dorylus wilverthi.
Although ants overall trend toward greater size in cooler places, Archibald notes that the eight largest living species dwell mostly in the tropics. The team looked at climate reconstructions for the fossil species and found hot spots where the ancient giants lived as well.
For a tropical lineage to have sprawled between continents meant taking ancient land bridges through Greenland or Iceland. During much of the ants’ time those northern routes were merely temperate. But brief hot spells were possible, Archibald and his colleagues say.
Climate scientists have already suggested there were several around 50 million years ago. One, for example, lasted about 170,000 years.
That idea of tropical moments of opportunity fits the interpretation of other fossils from the far north, says paleoclimatologist Appy Sluijs of Utrecht University in the Netherlands. Findings in northern regions of preserved hippo predecessors, tropical plankton and pollen from tropical palms support the idea. Now, he says, “The major challenge is to explain how a region that does not receive sunlight for six months keeps from freezing its giant ants and other creatures that don’t tolerate frost.”
Community ecologist Michael Kaspari of the University of Oklahoma in Norman has studied the cooler-bigger connection and says that so far he’s “agnostic” about whether supersized ant species have tropical tastes. In any case, he says, the new species ranks as “a magnificent ant.”