Anomalous two-tusked narwhals show no difference in diet or foraging ecology relative to normal narwhals
New research sheds light on one of the Arctic’s rarest biological phenomena—the two-tusked narwhal.
Narwhals are often called the Unicorns of the Sea, and are known for their single spiraled tusk—an erupted canine tooth that can grow up to three meters long. Occasionally, narwhals develop two tusks, a trait that has fascinated scientists and society for centuries.
An international research team led by researchers from Greenland Institute of Natural resources and University of Copenhagen investigated whether having two tusks or other unusual dental features influence the diet of narwhals. By integrating DNA-based sex identification and stable isotope analyses of bone collagen of narwhal specimens from museum collections, the researchers were able to reconstruct the sex and long-term aspects of each individual's feeding ecology.
“We wanted to know whether having two tusks or other dental anomalies could cause the animals to hunt and consume different prey,” said lead author Dr Marie Louis from the Greenland Institute of Natural Resources.
“Our results show that, despite this striking anatomical difference, two-tusked narwhals feed in similar areas and/or on similar prey as normal narwhals. But we found that individuals with dentition similar to beluga whales had very different ecologies relative to normal narwhals.”
The genetic analysis clearly showed that all two-tusked narwhals were male. This included a two-tusked narwhal collected in the Greenland Sea in 1684 that is housed in the Museum of Nature Hamburg, which is known as Mona Lisa. Our finding disputes the centuries-old assumption that the individual is the only female of its kind, based on reports that it was found in association with a foetus.
“Two-tusked narwhals remain an incredibly rare natural curiosity. Around 20 are known from museum collections worldwide, ten of which were included in our analysis” said Professor Eline Lorenzen of University of Copenhagen’s Globe Institute, who is senior author of the study.
“But from an ecological standpoint, they appear to live and feed just like their normal narwhal counterparts.”
About the Study
The study analyzed samples from both modern and historical collections, with the oldest double-tusked sample dating to 1684, and included isotopic comparisons across multiple narwhal populations. It contributes to ongoing efforts to understand how physical traits influence the ecology and evolution of marine mammals in rapidly changing polar environments.
Read the study published in Ecology and Evolution.
Media Contact
Senior Researcher Dr. Marie Louis, Greenland Institute of Natural Resources.
Email: marie.louis@natur.gl
Tel: +299 290226
Professor Eline Lorenzen, Globe Institute, University of Copenhagen.
Email: elinelorenzen@sund.ku.dk
Tel: +45 26701024