Hummingbird-sized ant fossils challenge what we know about insect size: ScienceAlert

More than 47 million years ago, giant carnivorous ants invaded the prehistoric forest floors of North America in search of prey.

“Giant” is not an exaggeration either. Some ancient colonies that lived in what is now the state of Wyoming were ruled by hummingbird-sized queens.

They’re not even the biggest ants to ever walk the Earth’s surface. The largest known queen ant to ever live was a relative found in fossil form in Germany. She had the body mass of a wren, was over 5 centimeters (2 inches) long, and had wings that spanned 16 centimeters. It is believed that his army of workers chased nothing in their wakeincluding possibly lizards, mammals and birds.

Like modern ants, these ancient insects were more than likely ectothermic, meaning they struggle to survive without an appreciable amount of heat in their environment. How far the temperature can drop before they manage to thrive largely depends on their body size.

While animals that can alter their own temperature resist colder climates by maximizing their mass and minimizing their skin, animals that need to absorb heat from their surroundings do better with more surface and less volume. Today, larger queen ants are found closer to the tropics, for example.

comparison of a hummingbird next to an ant fossil
The fossil of an extinct giant ant from Wyoming vs. a hummingbird for size. (Bruce Archibald)

So how did ancient giant ants cross the cold Bering Land Bridge that once connected Russia to Alaska on their way from Europe to Wyoming?

In 2011, researchers have suggested that this temperate land bridge once included a climate-controlled “gate”. During brief periods of global warming, this doorway may have opened to allow cold-blooded organisms, such as ants, to comfortably cross between continents.

A recently discovered fossil of an ancient queen ant now complicates this hypothesis.

giant ant germany
A fossil of a giant queen ant unearthed in Germany, the largest ant ever found. (Wikimedia Commons/CC BY 4.0)

It too belongs to the same genus as the giant ants found in Wyoming and Germany, called Titanomyrm.

But this one was found in British Columbia in Canada – the first fossil of its kind to appear in such a cold climate.

Scientists can’t be sure of its size due to its squashed nature, but there’s a chance it could be as large as its Wyoming counterpart.

“If it was a smaller species, was it adapted to this cooler climate region by reducing its size and gigantic species were excluded as we predicted in 2011?” wonders paleontologist Bruce Archibald of Simon Fraser University (SFU).

“Or were they huge, and our idea of ​​the climate tolerance of gigantic ants, and therefore how they traversed the Arctic, was wrong?”

Allenby Fossil
The giant fossil queen ant Titanomyrm discovered in the Allenby formation. (Bruce Archibald)

The Canadian Titanomyrm is not in very good condition, meaning it cannot be assigned to a specific species, but it is close in age to other such fossils found in Europe and Wyoming.

Depending on how it was compressed, the organism could originally measure 3 or 5 centimeters long.

The shorter estimate would make it 65% smaller than its Wyoming counterpart, supporting the idea that gigantic ants need warm climates and could only have been let through the climate gate of the Bering Land Bridge for a period of global warming.

The larger measurement suggests that these ancient ants had a greater cold tolerance than we thought and could have crossed the land bridge at any time.

The only way to tell these scenarios apart is to find more fossils.

“Are our ideas of Titanomyrms ecology, and therefore of this ancient dispersion of life, need to be revised? » asked Archibald.

“For now, it remains a mystery.”

The study was published in The Canadian Entomologist.

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