Dorsal-fin spine growth of Heterodontus portusjacksoni: a general model that applies to dorsal-fin spines of chondrichthyans?
Javier Tovar-Avila, Christopher Izzo, Terence I Walker, J Matias Braccini, Robert W Day
CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES | CANADIAN SCIENCE PUBLISHING | Published : 2008
A prospective model of dorsal-fin spine growth in chondrichthyans is devised by studying the growth of spines from captive and wild Heterodontus portusjacksoni injected with several fluorochromes. Evidence was found for only two dentine layers in the spine trunk of H. portusjacksoni, contrasting with conjectures about the presence of a third middle dentine layer in some squalids. The spines have three simultaneous growth zones. The first growth zone is along the internal edge of the inner trunk dentine layer, where growth bands are deposited towards the centre (centripetally), increasing spine length and width by pressure against the cartilage rod. The second growth zone is along the externa..View full abstract