Biotic vs abiotic factors promoting the diversification of caenophidian snakes.
Final Report Abstract
Advanced snakes of the clade Caenophidia constitute the majority of modern snake diversity, and fossil evidence suggests that their currently observed species richness is the result of a dramatic increase in diversification in the past 30 million years. One major proposition to explain this phenomenon is that that caenophidian snake evolution is related to the diversification of small endothermic vertebrates such as rodents and passeriform birds, which both constitute frequent prey items; alternatively, it has been suggested that changing climate and the associated evolution of more open habitats were the major driving factors. The principal aim of our project was to investigate to what extent these two different hypotheses can be considered relevant for caenophidian diversification, and/or if there are other, additional factors that need to be considered. In our project we therefore generated a) an extensive database of modern snake diets that we analyzed within a phylogenetic framework in order to investigate a potential relationship between caenophidian snake diversification and their prey; b) a database of fossil snake occurrences, partially complemented by personal analyses of African fossil snake records, which we used to determine proper fossil calibration points to date modern snake phylogenies and analyze caenophidian diversity through time; and c) a computed tomography database of modern snake skeletons that allows for the incorporation of fossil snake taxa within an integrative phylogenetic framework incorporating molecules, morphology, and fossils. Our results suggest that the traditional hypothesis of an increase in caenophidian snake diversification due to a coevolution between derived snakes and their prey (i.e. biotic interactions) can most likely be rejected, as we found no evidence for such a signal at larger phylogenetic scales. At the same time, our fossil diversity analyses point towards a relationship between caenophidian diversification and Neogene climate change. If correct, then this implies that abiotic factors like global cooling and the associated evolution of more open (i.e. grassland and savannah habitats) were important for caenophidian diversification. We suggest that these patterns clearly deserve further attention in the future and should be investigated also at the subclade level, including taxonomic revisions of fossil taxa. Also, our survey of the African fossil snake record resulted in the generation of several new faunal lists ranging from the Early Miocene to Late Pliocene. Finally, our extensive CT-based data set of modern snake morphology together with the consideration of recent advances in caenophidian snake phylogenetics allowed us to identify modern snake lineages previously unrecognized in the European fossil record, and will represent an important foundation for future integrative studies.
Publications
- (2012): Best practices for justifying fossil calibrations. – Systematic Biology 61: 346–359
Parham, J. F., Donoghue, P. C. J., Bell, C. J., Calway, T. D., Head, J. J, Holroyd, P. A., Inoue, J. G., Irmis, R. B., Joyce, W. G., Ksepka, D. T., Patané, J. S. L., Smith, N. D., Tarver, J. E., van Tuinen, M., Yang, Z., Angielczyk, K. D., Greenwood, J., Hipsley, C. A. , Jacobs, L., Makovicky, P. J., Müller, J. , Smith, K. T., Theodor, J. M., Warnock, R. C. & Benton, M. J.
(See online at https://doi.org/10.1093/sysbio/syr107) - (2013): An annotated checklist, description and key to the dwarf snakes of the Genus Eirenis JAN, 1863 (Reptilia: Squamata: Colubridae), with special emphasis on the dentition. – Vertebrate Zoology 63: 41-85
Mahlow, K., Tillack, F., Schmidtler, J.-F. & Müller J.
- Fossil calibration dates for molecular phylogenetic analysis of snakes 2: Caenophidia, Colubroidea, Elapoidea, Colubridae. – Palaeontologica Electronica, June 2016, Article number: 19.2.2FC
Head, J.J., Mahlow, K. & Müller, J.
(See online at https://doi.org/10.26879/625)
