Several giant ant fossils have been found in both Europe and North America. But how did these cold-intolerant insects manage to cross the only land bridge that still existed between the two continents 50 million years ago?
About ten centimeters long, that’s the size of the ants that roamed the ground of the North American continent 50 million years ago. This fossil of Titanomyrma was found in Princeton, Canada. It is not, however, the only giant ant specimen to have been discovered. Other fossils of the same age have indeed been found in the United States as well as in Germany and England. A geographical distribution that indicates that Titanomyrma succeeded in colonizing several continents at the beginning of the Eocene, when the Atlantic Ocean was already formed.
Where could these insects have passed? This is the question posed by a team of scientists. At that time, Europe and North America were still connected by land passages at the level of the Arctic, but this does not mean that the climatic conditions were favorable for the passage of ants. Because this kind of giant insect is rather typical of tropical regions, because of their intolerance to cold.
A passage through the Arctic during very hot periods
However, 50 million years ago, the climate was generally warm, but not warm enough to allow the passage of these insects through the Arctic zone. In 2011, researchers proposed that Titanomyrma would have taken advantage of short hyperthermic episodes, associated with very strong increases in temperature, to venture north and thus colonize the various continents. The discovery of the Princeton fossil, however, raises certain doubts as to the resistance to cold of Titanomyrmas. Indeed, the researchers did not expect to find them in a region subject to a temperate climate during the Eocene. The fossil, although large, is however difficult to measure because of the deformation it has undergone over time. If it is the largest species of Titanomyrma, then this suggests that these ants would ultimately have been more cold hardy than previously thought. If it is a smaller species, its adaptation to cold climates would have been better and it would thus have been able to cross the arctic passage more easily than the giant forms.
Only the discovery of new fossils can clarify this point. The results of this research have been published in The Canadian Entomologist.
