Form and Function

           Narwhals are well adapted to the arctic marine environment in which they live. Narwhals have a streamline body with two dorsal flippers and lack a dorsal fin. Propulsion comes from their tail. They have a thick layer of blubber to protect their bodies from the cold (Williams et al. 2011).

           Their bodies are specially adapted for deep dives. Narwhals have a compressible rib cage that sbidental narwhal skullupports their organs in deep water where pressures are extreme (Heide-Jorgensen & Garde 2011). Two other keys to the narwhal’s remarkable diving ability can be found in their muscles. First, narwhal muscles fibers contain twice the amount of myoglobin of other oceanic mammals, which allows their muscles to work longer (Williams et al. 2011). The composition of the narwhal muscle also assists them on long, deep dives. Narwhal muscle is made of primarily slow-twitch muscle fibers. These muscles fibers use oxygen more efficiently and are used for endurance instead of speed (Williams et al. 2011). These adaptations allow narwhals to go 25 minutes between breaths and to record some of the deepest dives ever recorded for a mammal at 1800m deep, which is greater than one mile (Williams et al. 2011).

           The scientific name for narwhal, Monodon monoceros, means “one tooth”, “one horn” (Heide-Jorgensen & Garde 2011). This name refers to the narwhal’s most recognizable feature, the tusk. Unlike other toothed whales, narwhals only have two teeth. These two teeth are both in the upper jaw. In males, the right tooth usually remains small and does not grow out of the mouth, while the left tooth grows into a tusk that can be 3 meters long (Curry 2010). A small percentage of males have two tusks, in which both teeth have grown into tusks, known as "bidental" narwhals. The tusks are spiraled with a counter clockwise rotation, relative to the narwhal (Curry 2010).  Ordinarily, females lack tusks. The purpose and function of their tusks has been widely speculated. Originally, it was believed that the tusks helped them hunt for food, or break breathing holes in the ice (Curry 2010). Today, researchers believe that the tusks are important in sexual selection. For example, the narwhal with the largest tusk would have the right to mate first (Curry 2010). Other researchers believe that the tusk is also filled with neurons and sensory cells that help the narwhal determine the conditions of its environment (Curry 2010; Williams et al. 2011). This would be advantageous to the narwhal during deep dives where there is no light and hunting would be primarily done by touch (Laidre 2004).

Photo credit: Sönke Behrends

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Created November 2013.