Meeting Abstract

54.4  Thursday, Jan. 6  Effects of body shape on myoseptal tendon ossification in teleost fishes DANOS, N*; WARD, AB; Harvard University; Adelphi University ndanos@oeb.harvard.edu

Fish body muscles are arranged along the vertebral column in three-dimensional W-shaped blocks, called myomeres. Each myomere is separated from its neighbours by a collagenous sheet, the myoseptum, and embedded in these myosepta and in positions that are conserved throughout gnathostome evolution are distinct tendons which often ossify. Ossification is usually intramembranous but can also be endochondral. Ossified myoseptal tendons are homologous to intermuscular bones and appear only in teleosts. The phylogenetic distribution of intermuscular bones has not been clearly demonstrated, although the presence and morphology of intermuscular bones has in the past been used to infer phylogenetic relationships. We sample over a broad phylogenetic range of teleost fishes to test 1) the effects of phylogenetic history on the presence of intermuscular bones and 2) morphological correlations to the presence of intermuscular bones. In humans, sesamoid bones can form in tendons that rub against bony protrusions and it has been shown that there is both a mechanical and a phylogenetic component to their incidence. Body and fin shapes as well as vertebral number and aspect ratio are characters that are likely to affect the distribution of stresses along the myoseptal tendons. Such morphological characters therefore could be good biomechanical predictors of myoseptal tendon ossification. We use the summary information by Patterson and Johnson (1995) for a list of species with intermuscular bones and reanalyze the homology of intermuscular bones to myoseptal tendons. Body shape morphometric data are obtained from photographs and x-rays of museum specimens. We find that after correcting for phylogeny there are still strong morphological predictors for the presence of all ossified tendons.