Comparative digital reconstruction of Pica pica and Struthio camelus and their cranial suture ontogenies

To date, several studies describe post-hatching ontogenetic variation in birds; however, none of these studies document and compare ontogenetic variation of the entire skull in multiple avian species. Therefore, we studied ontogenetic skull variation of two bird species with very different ecologies, Pica pica, and Struthio camelus, using mu CT based 3D reconstructions. For each specimen, we performed bone-by-bone segmentation in order to visualize and describe the morphological variation of each bone during ontogeny and estimated the average sutural closure of the skulls to identify different ontogenetic stages. Although bone fusion of P. pica occurs more rapidly than that of S. camelus the general sequence of bone fusion follows a similar trend from posterior to anterior, but a more detailed analysis reveals some interspecific variation in the fusion patterns. Although growth persists over a longer period in S. camelus than in P. pica and adults of the former species are significantly larger, the skull of the most mature S. camelus is still less fused than that of P. pica. Different growth and fusion patterns of the two species indicate that the interspecific ontogenetic variation could be related to heterochronic developments. Nevertheless, this hypothesis needs to be tested in a broader phylogenetic framework in order to detect the evolutionary direction of the potential heterochronic transformations.

Automated summary

This study investigates the ontogenetic skull variation of two bird species using mu CT based 3D reconstructions. The results show that although bone fusion occurs more rapidly in P. pica than in S. camelus, the general sequence of fusion follows a similar trend. However, a more detailed analysis reveals variation in fusion patterns between the two species. The different growth and fusion patterns suggest that the interspecific ontogenetic variation may be related to heterochronic developments, which should be further explored in a broader phylogenetic context.