HR: 0830h
AN: B31E-0365    [PDF]
TI: Stable Isotope Analysis of Extant Lamnoid Shark Centra: A New Tool in Age Determination?
AU: * Labs, J
EM: jlabs@ufl.edu
AF: University of Florida, Department of Geological Sciences 241 Williamson Hall, Ganiesville, FL 32611 United States
AU: * Labs, J
EM: jlabs@ufl.edu
AF: Florida Museum of Natural History, 216 Dickinson Hall, Gainesville, FL 32611 United States
AB: The oxygen isotopes of fourteen vertebral centra from ten extant lamnoid sharks (including {\it Carcharodon carcharias} [great white], {\it Isurus paucus} [longfin mako], and {\it Isurus oxyrinchus} [shortfin mako]) were sampled and measured along the growth axis to determine the periodicity of incremental growth represented in the centra. As part of the internal (endochondral) skeleton, shark centra are composed initially of hyaline cartilage, which then secondarily ossifies during ontogeny forming calcified hydroxyapatite bone. The incremental growth of shark centra forms definite growth rings, with darker denser portions being deposited during slower growth times (i.e., winter) and lighter portions being deposited during more rapid growth (i.e., summer). Thus, shark centra, whether they are extant or extinct, are characterized by clearly delineated incremental growth couplets. The problem with this general rule is that there are several factors in which the growth of these couplets can vary depending upon physical environment (including temperature and water depth), food availability, and stress. The challenge for paleobiological interpretations is how to interpret the periodicity of this growth. It can generally be assumed that these bands are annual, but it is uncertain the extent to which exceptions to the rule occur. Stable isotopic analysis provides the potential to independently determine the periodicity of the growth increments and ultimately the ontogenetic age of an individual.
DE: 0399 General or miscellaneous
SC: Biogeosciences [B]
MN: 2003 Fall Meeting