That's a hummingbird. (Courtesy of Bruce Archibald)
Wyoming about 50 million years ago would have been a terrible place to have a picnic. Look at the size of that fossilized giant ant – at more than 5 centimeters long, a few of them would eat your sandwiches and then carry away your date for dessert.
The extinct formicine ant, Titanomyrma lubei, was dug up in Wyoming's Green River Formation and had been sitting in a museum drawer until biologist Bruce Archibald stumbled upon it and realized its importance. Archibald and his colleagues believe that this is the first known giant ant in the Western Hemisphere and the first reported instance of a trans-Arctic migration by a heat-loving insect, according to a new study published in the Proceedings of the Royal Society B.
These ants might look fierce, but they were wimps when it came to weather.
Judging by where their fossilized bodies have been found, the creatures confined their wanderings to environments where the temperature was 68 degrees or above. Thus it was a mystery how these sensitive insects made their way from Europe to North America or vice versa. There was indeed a land bridge back then spanning the continents, but the Arctic weather was chilly enough to halt the migration of the ants.
The explanation, according to Archibald et al, lies in short-duration periods of climate change called hyperthermals. During the early Eocene period, the air would warm up for a couple hundred thousand years, perhaps due to CO2 leaking out of sediment, bringing the average Arctic temperature up to 48 degrees. The ants probably took advantage of these heat waves to scurry across the land bridge and colonize both continents.
You can read more about the discovery in this nice writeup from LiveScience.