Synchrotron microtomography‐based osteohistology ofGansus yumenensis: new data on the evolution of uninterrupted bone deposition in basal birds

Abstract

AbstractMany studies of the limb bones from birds of the major clades reveal a mosaic evolution in morphological characters. From this, we assume that uninterrupted compact bone evolved independently multiple times outside of the crown group. We hypothesise that there are key intraskeletal changes in the osteohistological features, such as the organisation of the vascular network. To test these hypotheses, we analysed and described the osteohistological features of five different midshaft samples ofGansus yumenensis, a non‐ornithurine Euornithes from China, based on virtual models obtained from synchrotron microtomography scans, a less invasive method that the traditional physical cross section. We performed quantitative analyses with volume, surface area and estimated ratios. The osteohistological features ofGansus yumenensiswere compared with those of stem and crown birds. From our analyses, we discuss the pros/cons of using synchrotron microtomography scans compared to traditional physical cross section. Our analyses demonstrate thatGansus yumenensisis the fourth described extinct Euornithes to exhibit uninterrupted bone deposition in all bone samples, providing further support for multiple origins of this feature outside of the bird crown group. Finally, our osteohistological investigation ofGansus yumenensisprovides future study avenues regarding the evolution and development of bone tissue in fossil birds.