Pre-primates lived in Canada some 52 million years ago

Do you know about the Eocene climatic optimum? It was during this period, about fifty-two million years ago, that the Earth experienced its warmest climate since the disappearance of the dinosaurs. The waters of the polar oceans were 12°C higher than today, and the average temperature of the Earth’s atmosphere was 10°C to 16°C higher than during the pre-industrial age – about 27°C – due to an intense greenhouse effect. No polar caps adorned Antarctica nor Greenland, and lush vegetation had advanced to the high latitudes, accompanied by a procession of animals.

It’s this warm and humid world that American paleontologist Mary Dawson (1931-2020) explored as a pioneer, leading expeditions to Ellesmere Island in the Canadian Far North in the 1970s. Facing the harshness of today’s climate, and undaunted by the polar bears and wolves haunting the area, she uncovered many unexpected vertebrates there, including curious pseudo-primate paromomyids, two species of which have just been described in the 25 January edition of the journal PLOS One.

“Mary Dawson had asked me to take over the study of these fossils, but for the last twenty years I was too engaged with other sites,” apologized Christopher Beard (University of Kansas), who coordinated the analysis of these fossils, which are essentially by jawbones and teeth. “The good news is that technology has progressed in the meantime, with microtomography now allowing very fine analyses of morphology in three dimensions.”

This has allowed two new species of the genus Ignacius to be identified, one named after Mary Dawson and the other after her colleague Malcolm McKenna (1930-2008), who also excavated in Ellesmere. Ignacius dawsonae must have weighed about 1,165 grams, and Ignacius mckennai not far from 2 kilograms. This makes them the largest representatives of the genus Ignacius which weighed only 100 grams when it appeared in what is currently Wyoming, more than sixty million years ago. This increase in weight from south to north corresponds to a rule established in 1847 by Carl Bergmann, who observed an increase in size in animals living in colder environments within the same clade [phylogenetic group possessing a common ancestor].

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The red arrows indicate possible dispersal routes of various mammals from North America to Ellesmere Island, Canada, about fifty-two million years ago. The white barrier indicates the closure of a land route between Europe and the American continent that would have previously allowed the movement of animals between these two regions.

But who are these Ignacius? They are members of the paromomyidae family, which populated both North America and Europe during the Eocene. This has fed the hypothesis of a land bridge between the two continents at that time. These species are not “true” primates but plesiadapiforms, an extinct group of mammals very close to primates,” said Séverine Toussaint (Humboldt University, Berlin). “There are still debates about their phylogenetic position. Some think that the primates would have come from another of the plesiadapiform families, but others suggest that the plesiadapiforms are instead a sister group to the primates.” “These fossils are not at all primates in the usual sense of the term,” confirmed Marc Godinot, emeritus director of research at the Paris Paleontology Research Center, who has been working on the origins of primates since the 1980s.

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