There were pseudo-primates in the Arctic 52 million years ago

Artist’s impression of a representative of the genus “Ignacius” who lived on the Canadian island of Ellesmere fifty-two million years ago. KRISTEN MILLER/BIODIVERSITY INSTITUTE/UNIVERSITY OF KANSAS

Do you know the climatic optimum of the Eocene? It was during this period, around fifty-two million years ago, that the earth’s climate experienced its warmest since the disappearance of the dinosaurs. The waters of the polar oceans were 12°C warmer than today, and the average temperature of the Earth’s atmosphere was 10°C to 16°C higher than during the pre-industrial age, i.e. about 27° C, due to an intense greenhouse effect. No polar cap adorned Antarctica or Greenland, and lush vegetation had progressed towards the high latitudes, accompanied by a procession of animals that are hard to imagine there.

It is this hot and humid world that the American paleontologist Mary Dawson (1931-2020) explored as a pioneer, leading expeditions to Ellesmere Island, in the Canadian Far North, in the 1970s. of the current climate, fearless in the face of the polar bears and wolves that haunt the place, she brought to light a number of unexpected vertebrates there, in particular curious paromomyids, pseudo-primates of which two species have just been described in the review PLOS One of January 25.

“Mary Dawson had asked me to take over the study of these fossils, but for twenty years I have been mobilized in other fieldsapologizes Christopher Beard (University of Kansas), who coordinated the analysis of these fossils, represented mainly by jaws and teeth. The good news is that technology has advanced in the meantime, with microtomography, which allows very fine analyzes of morphology in three dimensions. »

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These have made it possible to define two new species of the genus Ignatiusone named after Mary Dawson and the other in honor of her colleague Malcolm McKenna (1930-2008), who also excavated at Ellesmere.

The hypothesis of a land bridge between Europe and America

Ignatius Dawson must have weighed about 1,165 grams, and Ignatius McKenna not far from 2 kilograms, which makes them the largest representatives of the genus Ignatius which, when it appeared in present-day Wyoming, more than sixty million years ago, weighed only 100 grams. This increase in weight from South to North responds to a rule enacted in 1847 by Carl Bergmann, who had observed within the same clade an increase in size in animals living in colder environments.

The red arrows indicate the possible dispersal routes of different mammals from North America to Ellesmere Island, Canada, around 52 million years ago. The white barrier indicates the closure of a land route between Europe and the American continent which would previously have allowed the movement of animals between these two regions. PALEOGEOGRAPHY OF THE ARCTIC/COLORADO PLATEAU GEOSYSTEMS INC./2019

But who are these Ignatius ? They are members of the Paromomyidae family, which in the Eocene populated both North America and Europe – which fueled the hypothesis of a land bridge between the two continents at that time.

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