The Mesozoic bird Confuciusornis sanctus lived in one of the most complex ecosystems of the Early Cretaceous, alongside many dinosaurs, but its life history today remains poorly understood. Improving our understanding could be key in developing enhanced knowledge surrounding the reptilian/avian transition (Padian et al. 2001). Studies of C.sanctus are unique as hundreds of fossil specimens have been found in the Early Cretaceous (ca 125–120 Myr ago) lakes of north eastern China thus are available for analyses. These specimens have highlighted a significant amount of variation within the C.sanctus population particularly linked to plumage, with some individuals having a long pair of tail feathers (Chiappe et al. 1999; Fig.1). This finding is of significance as it has been interpreted by some as the first evidence of sexual dimorphism in birds (Feduccia et.al 1996; Hou et al. 1996).
There are ongoing arguments that conclusions surrounding sexual dimorphism in C.santcus are not substantiated by the available data and that interpretations of size variability and presence of tail feathers may involve alternative biological explanations. Therefore more robust tools to better assess age and sex of C.sanctus fossils are urgently required. In parallel, in modern bone biology, it has been found that this microstructure of mouse bone is sexually dimorphic, giving a potential novel method for assessing sex if this is also true for birds. The work will have significant implications for understanding the evolution of birds, and their behaviour.
- First, how bone microstructure is affected by sex and age will be assessed in a modern model species. Here, the starling (Sturnus vulgaris) is an appropriate choice because it is similar in size to C. sanctus
- This study will combine low- and high-resolution minimally invasive X-ray CT scans of starling femora from age-matched males and females for quantitative sex comparisons and 3D measurements of vascular size density and orientation. Previous work in mouse bone has found sexual dimorphism in bone vascular organisation. However, this is the first time the approach has been assessed in birds which may differ from mammals in how sex affects bone structure.
- Sex-matched adult and juvenile starling bones will be scanned and information extracted on cortical porosity focusing on osteocyte lacunae. We will undertake quantitative measures of osteocyte lacunar size, volume and distribution and will also develop unique measurements of osteocytes as a sex indicator. Lacunar and vascular reconstructions changes will be mapped with whole bone geometry measurements to identify if underlying sexual dimorphism which exits in bone microstructure can also be evidenced in overall bone shape.
- Isolated long bones and specimens of Confuciusornis (with and without tail streamers, and of different sizes) will then be scanned for analysis to determine maturity and sex. This will confirm whether Confuciusornis represents the first record of avian sexual dimorphism, and help resolve diversity within the genus.
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the School of Biological Sciences. Specific training will include:
- training in the use of CT scanning techniques
- development of novel methods for imaging fossils
- interpreting a fossil’s characteristics
- Williams, K. A., Gostling, N. J., Steer, J., Oreffo, R., & Schneider, P. (2021). Quantifying intracortical bone microstructure: a critical appraisal of 2D and 3D approaches for assessing vascular canals and osteocyte lacunae. Journal of Anatomy, 238:653–668.
- Sharma, A., Goring, A. L., Johnson, P., Boyde, A., Emery, R. J., Hesse, E., Olsen, B., Pitsillides, A. A., Oreffo, R., Mahajan, S., & Clarkin, C. (Accepted/In press). Multiscale molecular profiling of pathological bone resolves sexually dimorphic control of extracellular matrix composition. Disease Models and Mechanisms, 14(3), [dmm048116]. https://doi.org/10.1242/dmm.048116