Molecular development of fibular reduction in birds and its evolution from dinosaurs
Version of Record online: 4 MAR 2016
© 2016 The Author(s). Evolution published by Wiley Periodicals, Inc. on behalf of The Society for the Study of Evolution.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Volume 70, Issue 3, pages 543–554, March 2016
How to Cite
Botelho, J. F., Smith-Paredes, D., Soto-Acuña, S., O'Connor, J., Palma, V. and Vargas, A. O. (2016), Molecular development of fibular reduction in birds and its evolution from dinosaurs. Evolution, 70: 543–554. doi: 10.1111/evo.12882
- Issue online: 15 MAR 2016
- Version of Record online: 4 MAR 2016
- Accepted manuscript online: 17 FEB 2016 03:50AM EST
- Manuscript Accepted: 27 JAN 2016
- Manuscript Revised: 2 JAN 2016
- Manuscript Received: 26 JUL 2015
- Bird–dinosaur transition;
- fibula, IHH;
- mesozoic birds;
Birds have a distally reduced, splinter-like fibula that is shorter than the tibia. In embryonic development, both skeletal elements start out with similar lengths. We examined molecular markers of cartilage differentiation in chicken embryos. We found that the distal end of the fibula expresses Indian hedgehog (IHH), undergoing terminal cartilage differentiation, and almost no Parathyroid-related protein (PTHrP), which is required to develop a proliferative growth plate (epiphysis). Reduction of the distal fibula may be influenced earlier by its close contact with the nearby fibulare, which strongly expresses PTHrP. The epiphysis-like fibulare however then separates from the fibula, which fails to maintain a distal growth plate, and fibular reduction ensues. Experimental downregulation of IHH signaling at a postmorphogenetic stage led to a tibia and fibula of equal length: The fibula is longer than in controls and fused to the fibulare, whereas the tibia is shorter and bent. We propose that the presence of a distal fibular epiphysis may constrain greater growth in the tibia. Accordingly, many Mesozoic birds show a fibula that has lost its distal epiphysis, but remains almost as long as the tibia, suggesting that loss of the fibulare preceded and allowed subsequent evolution of great fibulo–tibial disparity.