'Giant' ant fossil questions dispersal of life 50 million years ago

A recent study led by Simon Fraser University paleontologists on the fossil remains of an extinct genus of ants is raising questions on how ancient animals and plants traveled between continents some 50 million years ago.

According to a press release, the distribution patterns of these organisms — which are being excavated now — across Europe and North America throw light on how climate change could have possibly changed their size and adaptability to harsh climate conditions. 

First of its kind in Canada, the preserved remains of the extinct giant queen ant Titanomyrma was discovered by a resident in the Allenby Formation of Princeton and was made available to the researchers through the town’s museum.

Interestingly, this extinct ant’s biggest species was surprisingly gigantic, with the body mass of a wren (small brown singing bird) and a wingspan of half a foot.

Following its discovery, the researchers compared it with another gigantic Titanomyrma fossil found a decade earlier, preserved in a Wyoming museum. 

The massive size of the queen ants was earlier associated with being either thermophilic or cryophobic

"This ant and the new fossil from British Columbia are close in age to other Titanomyrma fossils that have been long known in Germany and England," Bruce Archibald, the lead researcher, said in a statement. They found that modern ants with the largest queens inhabit only hot climates, almost exclusively in the tropics, leading them to associate large-size queen ants with high temperatures.

So the great size of queens is associated with being either thermophilic (an organism that thrives in high temperatures) or cryophobic (fear of extreme cold).

But this didn’t align with the fact that the ancient Arctic had a milder climate than today, meaning it wouldn’t have been hot enough to allow Titanomyrma to cross during any time when the land bridge was present (Europe and North America were connected by land across the Arctic then).

So how did these ants crossover?

The researchers suggested in 2011 that this might be explained by brief intervals of global warming creating short-term intervals of friendly conditions for them to cross.

The newly discovered Titanomyrma in Canada is incomplete, indistinctly preserved, and has been distorted in fossilization. So the true size of this fossil is unclear. Had it been small in size, it would have supported gigantism in Titanomyrma, meaning it would require a hot climate to pass. Whereas, if it had been large, the Titanomyrma may have been cold-winter intolerant and able to have crossed during any time.

Archibald says the research is helping scientists better understand how ancient animals and plants were formed when the climate was much different. 

“Titanomyrma may also help us better understand how global warming could affect how the distribution of life may change. To prepare for the future, it helps to understand the past.”

Simon Fraser University paleontologists Bruce Archibald and Rolf Mathewes, together with Arvid Aase of Fossil Butte National Monument in Wyoming, have published their research on the fossil in the current edition of the scientific journal The Canadian Entomologist.

Study Abstract:

We examine the implications for intercontinental dispersal of the extinct ant genus, Titanomyrma Archibald et al. (Hymenoptera: Formicidae: Formiciinae), following the discovery of its first fossil in Eocene temperate upland Canada. Modern Holarctic distributions of plants and animals were in part formed by dispersals across Late Cretaceous through early Eocene Arctic land bridges. Mild winters in a microthermal Arctic would allow taxa today restricted to the tropics by cold intolerance to cross, with episodic hyperthermal events allowing tropical taxa requiring hot climates to cross. Modern ants with the largest queens inhabit low latitudes of high temperature and mild coldest months, whereas those with smaller queens inhabit a wide variety of latitudes and climates. Gigantic and smaller formiciine ants (Titanomyrma and Formicium Westwood) are known from Europe and North America in the Eocene. The new Canadian Titanomyrma inhabited a cooler upland. It is incomplete, indistinctly preserved, and distorted in fossilisation, and so we do not assign it to a species or erect a new one for it. The true size of this fossil is unclear by this distortion: small size would support gigantism in Titanomyrma requiring hot climates and dispersal during hyperthermals; if it was large, it may have been cold-winter intolerant and able to have crossed during any time when the land bridge was present.