Data from: Phylogenetic variation in hind-limb bone scaling of flightless theropods

The robusticity of the weight-bearing limbs of large terrestrial animals
is expected to increase at a more rapid rate than in their smaller
relatives. This scaling has been hypothesized to allow large species to
maintain stresses in the limb bones that are similar to those seen in
smaller ones. Curvilinear scaling has previously been found in mammals and
nonavian theropods but has not been demonstrated in birds. In this study,
polynomial regressions of leg-bone length and circumference in terrestrial
flightless birds were carried out to test for a relationship similar to
that seen in nonavian theropods. Flightless birds exhibit curvilinear
scaling, with the femora of large taxa becoming thicker relative to length
at a greater rate than in smaller taxa. Evidence was found for nonlinear
scaling in the leg bones of nonavian theropods. However, unlike in avians,
there is also phylogenetic variation between taxonomic groups, with
tyrannosaur leg bones in particular scaling differently than other groups.
Phylogenetically corrected quadratic regressions and separate analyses of
taxonomic groupings found little phylogenetic variation in flightless
birds. It is suggested here that the nonlinear scaling seen in avian
femora is due to the need to maintain the position of the knee under a
more anterior center of mass, thereby restricting femoral length. The
femur of nonavian theropods is not so constrained, with greater
variability of the linear scaling relationships between clades.
Phylogenetic variation in limb-bone scaling may broaden the errors for
mass-predictive scaling equations based on limb-bone measurements of
nonavian theropods.