Long Bone Scaling in Neosauropod Dinosaurs

[Guy Leahy <xrciseguy@sbcglobal.net>]

Congrats to Dr. Bonnan...
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Anatomical Record (Hoboken). 2007 Aug
23;290(9):1089-1111 
Linear and Geometric Morphometric Analysis of Long
Bone Scaling Patterns in Jurassic Neosauropod
Dinosaurs: Their Functional and Paleobiological
Implications.Bonnan MF.
Department of Biological Sciences, Western Illinois
University, Macomb, Illinois.

Neosauropod dinosaurs were gigantic, herbivorous
dinosaurs. Given that the limb skeleton is essentially
a plastic, mobile framework that supports and moves
the body, analysis of long bone scaling can reveal
limb adaptations that supported neosauropod gigantism.
Previously, analyses of linear dimensions have
revealed a relatively isometric scaling pattern for
the humerus and femur of neosauropods. Here, a
combined scaling analysis of humerus and femur linear
dimensions, cortical area, and shape across six
neosauropod taxa is used to test the hypothesis that
neosauropod long bones scaled isometrically and to
investigate the paleobiological implications of these
trends. A combination of linear regression and
geometric morphometrics analyses of neosauropod humeri
and femora were performed using traditional and
thin-plate splines approaches. The neosauropod sample
was very homogeneous, and linear analyses revealed
that nearly all humerus and femur dimensions,
including cortical area, scale with isometry against
maximum length. Thin-plate splines analyses showed
that little to no significant shape change occurs with
increasing length or cortical area for the humerus or
femur. Even with the exclusion of the long-limbed
Brachiosaurus, the overall trends were consistently
isometric. These results suggest that the mechanical
advantage of limb-moving muscles and the relative
range of limb movement decreased with increasing size.
The isometric signal for neosauropod long bone
dimensions and shape suggests these dinosaurs may have
reached the upper limit of vertebrate long bone
mechanics. Perhaps, like stilt-walkers, the absolutely
long limbs of the largest neosauropods allowed for
efficient locomotion at gigantic size with few
ontogenetic changes. 
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Guy Leahy