Meeting Abstract
P3.105 Sunday, Jan. 6 Proportions and distribution of mass in the hindlimbs of neognath birds KILBOURNE, B.M.; Friedrich-Schiller-Universität Jena brandon.kilbourne@uni-jena.de
While scale effects on avian hindlimb segment lengths and proportions have been studied in depth, the influence of size upon the proportions of segment masses remains unexplored. Furthermore, it is also unknown how individual segment masses contribute to the mass distribution of the overall hindlimb. To understand the influence of body and hindlimb size upon the mass proportions of avian hindlimbs, I collected data on body mass, hindlimb segment masses, and hindlimb length in 22 species of neognath birds. The species sample contains at least one representative of seven major neognath lineages and reflects a range of ecological specializations, and masses were recorded from the femoral, tibiotarsal, and tarsometatarsal segments, as well as the digits. Prior to dissecting limb segments from one another, I measured the center of mass (COM) position of the entire hindlimb relative to the femoral head. To understand the scaling of hindlimb COM position and segment masses, I tested empirical scaling relationships against the null model of geometric similarity. COM position scales with positive allometry relative to body mass but does not deviate from geometric similarity when scaling against hindlimb length. Thus, hindlimb mass shifts distally relative to body mass as body size increases in neognaths. Segment masses scale with isometry relative to both body mass and hindlimb length. The allometric exponent (0.41) when scaling hindlimb length against body mass is well above the prediction of geometric similarity (0.33), and the relationship between hindlimb length and body mass determines how COM position scales with body mass. Specifically, the results suggest that the positive allometry COM position is due to large-bodied neognath species having more extended hindlimbs than small-bodied neognaths and not due to differences in the mass of individual hindlimb segments.
