Differences between sliding semi‐landmark methods in geometric morphometrics, with an application to human craniofacial and dental variation

Abstract

Over the last decade, geometric morphometric methods have been applied increasingly to the study of human form. When too few landmarks are available, outlines can be digitized as series of discrete points. The individual points must be slid along a tangential direction so as to remove tangential variation, because contours should be homologous from subject to subject whereas their individual points need not. This variation can be removed by minimizing either bending energy (BE) or Procrustes distance (D) with respect to a mean reference form. Because these two criteria make different assumptions, it becomes necessary to study how these differences modify the results obtained. We performed bootstrapped-based Goodall's F -test, Foote's measurement, principal component (PC) and discriminant function analyses on human molars and craniometric data to compare the results obtained by the two criteria. Results show that: (1) F -scores and P -values were similar for both criteria; (2) results of Foote's measurement show that both criteria yield different estimates of within-and between-sample variation; (3) there is low correlation between the first PC axes obtained by D and BE; (4) the percentage of correct classification is similar for BE and D, but the ordination of groups along discriminant scores differs between them. The differences between criteria can alter the results when morphological variation in the sample is small, as in the analysis of modern human populations.

Claw morphometrics in monitor lizards: Variable substrate and habitat use correlate to shape diversity within a predator guild

“…The two traced margins were transformed into 30 equidistant coordinates, and the coordinates at the tip were combined into one. This resulted in three landmarks and 56 semilandmarks, the latter of which were slid to minimize the bending energy (Gunz & Mitteroecker, 2013; Perez, Bernal, & Gonzalez, 2006) using TpsRelw 1.53 (Rohlf, 2013). This program also performed a generalized least squares Procrustes superimposition on the data, and calculated centroid size (CS).…”

Talking heads: Morphological variation in the human mandible over the last 500 years in the Netherlands

“…Concerning the sliding semilandmarks algorithm, it was decided that the minimum Procrustes distance criterion should be used. With this criterion, the differences in semilandmark positions along the curve between the reference form and each specimen are removed by estimating the direction tangential to the curve and removing the component of the differences along this tangent (Perez et al, 2006).…”

A geometric morphometric study into the sexual dimorphism of the human scapula

“…Sliding semi-landmark geometric morphometric methods have also been employed in a number of studies (De Groote et al, 2010;Gonzalez et al, 2009;Perez et al, 2006). The sliding semi-landmark method is used when the structure being studied has too few or no identifiable landmarks.…”

“…The curve data method that was used in this study was similar to the methods used by Perez et al (2006), however, in this study sliding semi-landmarks were not used, as these methods could not be analyzed using the IMP package.…”