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"The difference is that they are not oriented in the same way," she said. "In humans, they are perpendicular to airflow, so when they close together they stop airflow. In whales, the vocal folds are parallel to airflow. Their orientation allows them to regulate the air in and out a reservoir called a laryngeal sac." When the sac expands in whales, it allows air to be shunted between it and the lungs, she explained. This permits more efficient extraction of oxygen from the limited volume of air, because it turns over what scientists call "respiratory dead space," or air not in contact with lung tissue. In the process of shunting air, pygmy right whales may also be vibrating the vocal folds to make noise. By exhaling into the sac, they are also pushing air between the vocal folds, causing vibrations that make sounds. Repetitive shunting allows air to be "recycled" inside the whale, allowing it to continue making sounds for a long time while submerged. Reidenberg said she "expects to find that the laryngeal sac is asymmetrical, which is unusual in baleen whales." It's not yet clear, she added, whether this is an elaboration of the midline sac position of other whales, or is closer to the ancestral condition of paired sacs, except that one has been lost. "Answering this question may help us understand evolutionary relationships between different species of whales," she said. The dissection is expected to continue for the rest of the week. Related Links: Jennifer Viegas' blog: Born Animal |
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