In 1976, as jackhammers and backhoes carved a subway tunnel through the glacial clays beneath Canada’s largest city, construction crews unearthed a surprise: the partial skull and antlers of a mysterious prehistoric deer.
The fossil, lifted from an excavation pit near Islington Station on Toronto’s western edge, bore antler beams so thick and oddly horizontal that no scientist could match them to a living species. Eventually some paleontologists named it Torontoceros hypogaeus, meaning “horned Toronto deer from underground.” More commonly, it was called the Toronto Subway Deer.
But the specimen, estimated to be at least 11,000 years old, set off decades of debate. Was this animal a strange relative of caribou? Or evidence of an altogether different deer that hit an evolutionary dead end?
After nearly 50 years, the deer has given up its secrets. Using ancient DNA extracted from the fossil, researchers have shown that, in spite of its size and large antlers with a caribou-like branching point, the subway deer was most closely related to mule deer and white-tailed deer, two smaller cervids still common across North America.
The study authors, led by Aaron Shafer, a population geneticist at Trent University in Ontario and a graduate student he worked with, Camille Kessler, now at Ludwig Maximilian University in Munich, posted their findings online in September. The paper is expected to be published soon in the journal Biology Letters.
“It’s very exciting,” said Roman Croitor, a paleontologist at Moldova State University with a specialty in deer fossils. In his own research, he had grouped Torontoceros with caribou. Had he suggested on the basis of antler shape that it was closer to mule or white-tailed deer, “people would have said I’m crazy,” he said.
But just as DNA evidence can overturn shaky witness accounts in a murder case, so, too. does genetic analysis deliver the final verdict in paleontology, Dr. Croitor acknowledged.
According to the DNA, Torontoceros most likely split from a tangle of evolving deer lineages around two million years ago and took shape as a distinct species. It roamed the open landscapes around the Great Lakes alongside mammoths, mastodons and other ice age giants. But as the climate warmed and forests overtook the plains, its habitat disappeared and, with it, nearly every trace of the species itself.
The lone subway deer specimen, held at the Royal Ontario Museum in Toronto, is now all that remains. An artist’s rendition included in Dr. Shafer’s paper depicts the deer as a cross between Sven from Disney’s “Frozen” and the stag from HBO’s “Game of Thrones.”
While a single specimen allows only a starting point for reconstructing its place in evolution, experts think there may be kindred samples lurking in museum drawers — mislabeled, overlooked or unidentified, and waiting for the tools of modern genetics to reveal their true identity.
“It is possible that there are other skeletal remains of this distinct lineage,” said Charlotte Lindqvist, an evolutionary geneticist at the University at Buffalo not involved in the study.
Precedent for this kind of fossil reclassification came recently from a humanlike skull unearthed in China. Originally described as a species of its own, the fossil was re-identified through molecular analysis as Denisovan, a lineage of ancient humans that diverged from Neanderthals and persisted in Asia for hundreds of thousands of years before going extinct. A similar twist could yet unfold with long-lost relatives of the Toronto subway deer.
C.S. “Rufus” Churcher, the University of Toronto paleontologist who first characterized the fossil, finds this prospect enticing — and he is encouraged by the potential of genetic technologies to clarify lingering uncertainties around the deer’s origins and evolutionary ties.
“The fact that we only have one animal is frustrating beyond belief,” said Dr. Churcher, now 97 and retired. “We would like to have more bits and pieces so we can tie it down more strongly.”
Investigating the lost deer’s ancestry is about more than solving a paleontological puzzle, though. “It’s a tangible connection to a distant past,” said Rob MacDonald, president of ASI, an archaeological consulting firm in Ontario — and its story offers a reminder of the risks species face as the climate shifts again.
The Royal Ontario Museum is in the middle of a large renovation project. But when its mammal fossil gallery reopens in a year or two, Burton Lim, a curator of mammal collections there and a study co-author, said he planned to showcase the subway deer more prominently.
Buoyed by the new DNA findings, Dr. Lim hopes the exhibit will capture public interest, highlighting how a single local fossil, unearthed by chance during a subway dig, preserved for decades in a museum and re-examined with modern technology, can reshape the understanding of the region’s natural history and past extinction events.
“It tells us a story that’s not often told,” Dr. Kessler said.
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