Hello morphometricians, I am relatively new to morphometrics, and I am attempting to assess ontogenetic trajectories from a longitudinal sample of growth study x-rays. My subjects are divided into 2 groups, and I would like to determine whether there are developmental differences in cranial shape between these groups. I have precise ages for each subject, so I hope to use age as a variable (following McNulty et al., 2006) rather than centroid size.
>From what I gather from the literature, I can estimate ontogenetic >trajectories by regressing the Procrustes aligned shape coordinates onto the >independent variable of age. So far, I have attempted to do this in the >geomorph package in R using the procD.lm and the trajectory.analysis >functions. I am wondering if I am doing this correctly, or if there is a >better function to use. I have tried the following: lateral.gpa <- gpagen(vaultlandmarks) procD.lm(two.d.array(lateral.gpa$coords) ~ age, iter = 999) where “vaultlandmarks” refers to the 2D landmark and semi-landmark coordinates in my tps file, and “age” refers to a column in my metadata csv file which gives the age of each specimen to the nearest 1/10 of a year. This provides a sum-of-squared Procrustes distances, a mean square, and a highly significant p-value. I am not sure, however, how to compare the results I get from the 2 groups. When I try the trajectory.analysis function: lateral.gpa <- two.d.array(gpagen(vaultlandmarks)$coords) trajectory.analysis(lateral.gpa~age) I get the error message: “Error in trajectory.analysis(lateral.gpa ~ age) : X-matrix does not specify enough model factors (see help file).” Thank you for any advice or help you might provide. Best, Miranda Karban PhD Candidate, University of Iowa -- MORPHMET may be accessed via its webpage at http://www.morphometrics.org To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
