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Prehistoric Toronto: The Ice Age

Throughout the world, the Pleistocene epoch was known for its giant mammals. Toronto was no exception.


Mammoths roamed present-day Toronto during the Pleistocene epoch.

Two-and-a-half-million years ago, Toronto suddenly found itself entering an ice age. The Pleistocene epoch, marked by four major glaciations, and many smaller ones, had arrived.

The Cenozoic era was already more than 60 million years old, and the once-humble survivors of the extinction that brought the age of dinosaurs to an emphatic end were thriving: mammals had previously been unable to compete with the bigger, faster reptiles that preyed upon them, but—immediately following the dinosaurs’ extinction—they stepped in to fill the ecological void.

They grew both in number and in species diversity. By the Pleistocene, many had grown, also, to giant size.

And two of the largest of these—the mammoth and the mastodon—once called Toronto home.

We have evidence: the alternating glacial tills and interglacial lake sediments that represent the sudden reappearance of our rock record during the Pleistocene have yielded fossilized remains. “It just seems strange to us to think that there were elephant-like creatures walking around in Toronto,” says Kevin Seymour, the Royal Ontario Museum’s assistant curator of vertebrate paleontology. “But, in the very recent past, just some thousands of years ago, it was true.”

The mastodon was fractionally smaller than its relative, the mammoth.

In behaviour and appearance, it is likely that both these creatures were relatively similar to their present-day cousin, the elephant. Certainly, they were similarly massive. The mastodon stood as many as three metres tall at the shoulder, the mammoth even taller on its long front legs. Ivory tusks, curved on the mammoth and straighter on the mastodon, grew to ridiculous lengths from the animals’ mouths.

While these tusks might have been useful for sparring, for knocking over trees, or for scraping snow off of delicious vegetation, their primary function may well have been in sexual selection. “The males that are in good health and robust, they can afford, energetically, to produce bigger tusks,” says Seymour. “And females cue in on that when it comes to mating time.”

Pleistocene Toronto was also within the habitat range of a rodent called the giant beaver.

“The beaver and the giant beaver have a common heritage back 20 million years ago or so, maybe deeper in time,” says Seymour. “Those two lineages diverged a long time ago.” This means it’s possible that the giant beaver—which grew to fully twice the size of its surviving relative—may have been a beaver in name only. There is no evidence, for instance, to suggest that it built dams. It’s possible that it looked and behaved more like a giant muskrat.

“The common name skews our conception of what [the giant beaver] was like,” Seymour says. “We don’t have direct evidence that they had a big tail like a beaver. They had the basic big incisor and the chewing mechanism, but they may have not used it in the same way as a beaver does today.”

A single tooth is the only piece of evidence the giant beaver has left us of its time in Toronto.

At exactly which point during the Pleistocene these animals existed here is uncertain, and they may well have come and gone repeatedly over time. As successive glaciers covered the terrain that would eventually become Toronto, plant and animal life moved south accordingly. This led to the creation of new ecosystems, as some species needed to move further than others in order to survive the changing climate.

When the glaciers periodically retreated, these jumbled ecosystems were shuffled once more as life returned to the newly re-exposed land. Huge tills of soil and other collected debris were deposited, divided here and there by streams of water running off the melting ice. Seeds and pollen blew in from other places. Plants began to grow. Herbivores returned. Then carnivores.

“Pretty soon,” Seymour says, “things start to come back. Nature abhors a vacuum; I think that’s an old adage that’s basically true. If you plow an area, cut down all the vegetation, and leave an open field, and then go away and come back in 20 years, there’ll be plants there. I guarantee you.”

The latest of these ecosystem regenerations over Toronto began some 12,000 years ago, when the city was just emerging from beneath the final Pleistocene glacier. The recent appearance of the opossum here suggests that the process is still ongoing.

But the retreating ice had a bearing on more than just plant and animal life. For a brief time, meltwater swamped the whole of what is now downtown under a vast glacial lake, the shoreline of which is still visible in Toronto today.