Some (finalish) results!

Matt and I have been meeting weekly for the past three weeks to have ODP work days–just to crank through analyses, etc. Mostly, it’s a matter of sitting down and forcing each other to do stuff. Matt’s posting soon, but in the meantime I thought I’d throw out some “final” results. These are regressions on phylogenetically independent contrasts (PICs), with analyses considering the whole sample, unequivocal quadrupeds (following Maidment and Barrett’s assignments), and unequivocal bipeds (following Maidment and Barrett, again).

A few quick notes (all of which are going into the main article text at some point)…PICs were calculated in the PDAP package of Mesquite. Limb lengths were log-transformed prior to analyses (which helped to move things towards normality a little bit, but not entirely). Branch lengths were initially set to divergence times, but we found that these violated the assumptions of PICs, and thus some transforms were used (to be outlined in the manuscript as well as a future post, once we’ve pulled that text together).

Below, I’m including the preliminary results text for this part of the analysis, the associated table, and table caption. Enjoy! And feel free to throw in some comments if you have any.

RESULTS
Intra- and interlimb scaling
Analyses including all taxa as well as analyses considering only unequivocal quadrupeds showed similar scaling patterns. Forelimb length scaled with strong positive allometry relative to hind limb length, whereas the distal hind limb elements (tibia and metatarsal III) collectively scaled with strong negative allometry relative to femur length. The distal forelimb (radius and metacarpal III) scaled isometrically relative to the humerus; however, we note that the lower confidence interval for the entire sample only barely excludes positive allometry. We thus speculate that a larger sample may ultimately demonstrate positive allometry.
When considering only unequivocal bipeds, none of the slopes differed from isometry. However, we note that this subset of taxa also had some of the smallest sample sizes considered here, and a larger sample might uncover allometric scaling patterns.

Table. Results of RMA (reduced major axis) regressions of PICs (phylognetically-independent contrasts) for logged limb segment lengths in ornithischian dinosaurs. In the “Allometry” column, “0” indicates a slope indistinguishable from isometry, “+” indicates a slope consistent with positive allometry, and “-” indicates a slope consistent with negative allometry. The numbers in parentheses in the “Slope” indicate the 95 percent confidence interval for the slope.

Grouping	X	Y	Allometry	Slope	R2	N
All	Humerus	Distal Forelimb	0	1.139 (0.996–1.301)	0.78	50
All	Femur	Distal Hind Limb	–	0.812 (0.715–0.921)	0.77	59
All	Hindlimb	Forelimb	+	1.301 (1.198–1.413)	0.94	39
Quadruped Only	Humerus	Distal Forelimb	0	1.138 (0.929–1.393)	0.72	29
Quadruped Only	Femur	Distal Hind Limb	–	0.742 (0.581–0.949)	0.57	30
Quadruped Only	Hindlimb	Forelimb	+	1.237 (1.027–1.489)	0.84	21
Biped only	Humerus	Distal Forelimb	0	0.829 (0.588–1.17)	0.75	11
Biped only	Femur	Distal Hind Limb	0	0.903 (0.739–1.105)	0.80	22
Biped only	Hindlimb	Forelimb	0	1.009 (0.543–1.876)	0.23	10

Regressions for PICs including the entire sample. The blue line indicates isometry.