The shadow of forgotten ancestors differently constrains the fate of Alligatoroidea and Crocodyloidea
Article first published online: 6 NOV 2008
© 2008 The Authors. Journal compilation © 2008 Blackwell Publishing Ltd
Global Ecology and Biogeography
Volume 18, Issue 1, pages 30–40, January 2009
How to Cite
Piras, P., Teresi, L., Buscalioni, A. D. and Cubo, J. (2009), The shadow of forgotten ancestors differently constrains the fate of Alligatoroidea and Crocodyloidea. Global Ecology and Biogeography, 18: 30–40. doi: 10.1111/j.1466-8238.2008.00426.x
- Issue published online: 9 DEC 2008
- Article first published online: 6 NOV 2008
- climatic change;
- functional performance;
- geometric morphometrics;
- rostral shape;
- variation partitioning
Aim We tested the hypothesis that the evolutionary fates of two sister groups (Alligatoroidea and Crocodyloidea) are differently constrained by phylogenetic and ecological (functional) factors in the face of climatic change.
Methods We quantified disparity in skull rostrum shape by means of geometric morphometrics. Mechanical performance of the rostrum was analyzed by applying beam theory calculations to morphological data and experimentally measured bite force. The phylogeny was expressed in the form of principal coordinates, the first ones of which were used as a set of explanatory variables. Extents of species occurrence were computed using species distribution maps. Finally, species maximum skull size were measured and considered as a proxy of maximum body size. We performed variation partitioning analyses in order to compare differential contributions of phylogenetic and ecological factors in Alligatoroidea and Crocodyloidea.
Results Alligatoroidea show higher ‘pure’ historical components than Crocodyloidea in explaining both rostrum shape and extent of occurrence (after controlling for body size). On the contrary, geometric variation of skull rostra of Crocodyloidea unequivocally shows a higher ‘pure’ functional component (linked to performance on prey capture) and a higher phylogenetically structured environmental variation than those found in Alligatoroidea. Results obtained for body size variation are consistent with these patterns. In Alligatoroidea, body size variation contains a higher phylogenetic signal than in Crocodyloidea.
Main Conclusions Our results suggest that Crocodyloidea and Alligatoroidea may react differently when faced with significant environmental changes. We predict that global climatic changes will have a more important effect on Crocodyloidea than in Alligatoroidea by (1) promoting trait shift, adaptation to the new diet and speciation and (2) modifying the geographical range distribution of species (which may track favourable ecological conditions).