Anomalous two-tusked narwhals show no difference in diet or foraging ecology relative to normal narwhals Published 12.12.2025

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Figure 1 Sampling of a two-tusked narwhal at the Natural History Museum of Denmark, University of Copenhagen for DNA and stable isotope analysis. Photo taken by Abdi Hedayat, Natural History Museum of Denmark.
Figure 2 The two-tusked narwhal known as Mona Lisa from the Museum of Nature Hamburg, courtesy of Mentz/Centrum für Naturkunde - Universität Hamburg . It has since it was collected in 1684 from the Greenland Sea been believed to be the only female of its kind.

 

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.” “Our study also highlights the importance of natural history collections and sample archives such as those at the Greenland Institute of Natural Resources, to address questions in biology.”

 

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.

 

For more information contact: 

Senior Researcher Dr. Marie Louis, Department for Birds and Mammals, Greenland Institute of Natural Resources, Email: marie.louis@natur.gl Tel: +299 361200