1Paleoanthropology Group, Museo Nacional de Ciencias Naturales (CSIC), 2Biology, Autonoma University Madrid (UAM), 3Radiology, Medizinische Universität Innsbruck, 4Department of Anatomy and Anthropology, Sackler Faculty of Medicine, Tel Aviv University, 5Faculty of Medicine Galilee, Bar Ilan University, 6Antropologia fisica, Sociedad de Ciencias Aranzadi, 7Anatomía y Embriología Humana II, Universidad Complutense, Madrid, 8Hull York Medical School (HYMS), The University of York
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Detailed knowledge of 3D-thoracic growth is poor despite the obvious morpho-functional implications for respiratory function, and the development and evolution of body shape. A major problem in studying ribcage growth is the difficulty to quantify the 3D-curvature and relations of the ribs and spine. Thus, most studies have so far relied on analyzing traditional measurements such as distances and indices on single or a few ribs.
On the basis of such analyses it is currently known that: 1) adult-like thoracic shape is achieved early, by the end of the second postnatal year, transforming the circular cross-section of the newborn thorax to the ovoid shape of adults; and 2) that the ribs become inclined such that their anterior borders are inferior to their posterior ones.
We revisit growth changes by using geometric morphometrics. We digitized 402 (semi)landmarks on 3D reconstructed ribcages to assess growth changes in 24 CT-scanned modern humans representing newborns to adults of both sexes.
Our analyses show a curved ontogenetic trajectory. Adult thoracic morphology is achieved later than predicted, by diverse modifications in different anatomical regions during different ontogenetic stages. Besides a marked relative increase in antero-posterior dimensions, there is increase in medio-lateral dimensions in the upper thorax, relative to a decrease in the lower thorax. This transforms the pyramidal-shaped infant thorax into the barrel-shaped one of adults. Rib descent is produced by complex changes in 3D curvature.
We discuss developmental differences in upper and lower thorax units regarding respiratory function and the ontogeny of body shape.
Funding: CGL2009-09013, CGL2012-37279, (Spanish Ministry for Economy and Competition), Fyssen-foundation.