This was published in 2005 but only recently came to my attention. The narwhal’s tusk is a sensor that can detect changes in water temperature, pressure, and chemical gradients.
Harvard Gazette: Marine biology mystery solved.
Professor of Biology
Warren Litsky '45 Endowed Chair in Biology
Worcester, Mass. 01610
Lasry Center for Biosciences
224 (lab) 231 (office)
curriculum vitae (pdf)