ARCTIC The Spiral in the Tusk of the Narwhal
ABSTRACT. The spiral in the tusk of the narwhal has been fancifully, but never satisfactorily, explained. Spiral growths are common in the animal kingdom and share the feature of having straight axes. A curved tusk would hinder the narwhal swimming; a spiral mode of growth ensures overall straightne...
| Main Authors: | , |
|---|---|
| Other Authors: | |
| Format: | Text |
| Language: | English |
| Published: |
1987
|
| Subjects: | |
| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.557.1108 http://pubs.aina.ucalgary.ca/arctic/Arctic41-3-236.pdf |
| Summary: | ABSTRACT. The spiral in the tusk of the narwhal has been fancifully, but never satisfactorily, explained. Spiral growths are common in the animal kingdom and share the feature of having straight axes. A curved tusk would hinder the narwhal swimming; a spiral mode of growth ensures overall straightness even if the tusk grows irregularly. The need to keep the tusk straight completely and satisfactorily explains the spiral. Key words: Monodon monoceros, dentition, morphology, asymmetry RÉSUMÉ. On a explique le fait que la come du narval soit spiralte de manitre originale mais jamais satisfaisante. Les croissances en spirale sont un phénombne commun dans le &gne animal et lles posstdent toutes la caracttristique d’avoir des axes rectilignes. Une come incurvte gênerait la nage du narval; une croissance s~iralée assure Que l’ensemble est rectiligne même si la come pousse de façon Mgulière. La ntcessitt pour la come de pousser droit justifie entièremedt et elle seule le phtnomtne de la spiale. Mots clés: Monodon monoceros, dentition, morphologie, asymttrie Traduit pour le journal par Ntsida Loyer. The tusk of the narwhal (Monodon monoceros) is remarkable in several ways: it is unique among the whales; it is straight; it usually only develops on the left side; and when, rarely, both left and right tusks develop, they both twist left-handed instead of mirroring each other (Thompson, 1942). Its phylogeny and |
|---|