Perrin, William F.; Würsig, Bernd; Thewissen, J. G. M., eds. (2008-11-24). "Earless Seals 24 Mart 2020 tarihinde Wayback Machine sitesinde arşivlendi.". Encyclopedia of Marine Mammals (2nd ed.). Burlington, Massachusetts: Academic Press. p. 346. ISBN 978-0-12-373553-9.
Perrin, William F.; Würsig, Bernd; Thewissen, J. G. M., eds. (2008-11-24). "Earless Seals 24 Mart 2020 tarihinde Wayback Machine sitesinde arşivlendi.". Encyclopedia of Marine Mammals (2nd ed.). Burlington, Massachusetts: Academic Press. p. 346. ISBN 978-0-12-373553-9.