In a recent study published in the Journal of Anatomy Richard Abel, from Imperial College London, and Gabriele Macho, from Institut Català de Paleontologia Miquel Crusafont, show how trabecular orientation in the ilium might help to learn about the positional and locomotor behaviour of species.

We could have guessed that from looking at the pelvis. Indeed, hominin fossil remains of ilia, i.e. the largest bones of the pelvis, have long provided evidence for the bipedal locomotion of our earliest ancestors. The shape of our ilia and their internal trabecular bundle arrangement are largely genetically determined, following the results of the recently published paper “Ontogenetic changes in the internal and external morphology of the ilium in modern humans” that presents a research based on 73 modern human ilia. But there is a twist.

The pelvis undergoes important remodelling throughout ontogeny and into adulthood: the shape of the ilium and its internal trabecular orientation are predetermined and develop synchronically until adolescence is reached, even though there are considerable changes in locomotor patterns throughout development from crawling to fully competent bipedal striding. At the onset of puberty however, growth of the external bone dimensions slows and eventually ceases, while that of the internal structures continues.

Adolescence is marked by an increase in muscle mass and body fat; these changes mainly occur after linear growth has stopped. Inevitably, these changes in body mass and proportions will affect the way in which the pelvis is loaded both during standing and in locomotion. To accommodate these new demands on an ilium, that has already attained its adult shape, the internal trabecular structures, such as thickness and spacing, are modified and the bundles are rearranged in relation to external landmarks.

Thus, even though the early definition of trabecular struts in the ilium appears species-specific, its potential for extended growth and realignment later in life may hold important information for the reconstruction of positional/locomotor behaviour from adult bones; inferences from external bone shape may be more limited due to developmental constraints. If confirmed, a broader knowledge of trabecular strut origins and (re)modelling that complements current knowledge based on the external pelvis shape, will boost our interpretations of the positional and locomotor behaviour of extinct species.

+ info Abel, R. & Macho, G. A. (2011). Ontogenetic changes in the internal and external morphology of the ilium in modern humans. Journal of Anatomy, 324 -335.