Impact of megafauna extinction on body size distribution in tortoisesJulia Joos1,2*, Catalina Pimiento3,4, Donald B. Miles1, Johannes Müller2

1Department of Biological Sciences, Ohio University, Athens, OH 45701, USA 2 Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, D-10115 Berlin, Germany* jj064318@ohio.edu

IntroductionThe Late Quaternary is characterized by the extinction of many terrestrial megafauna species. Giant tortoises were abundant all over the world throughout the Neogene, but only persisted on the Galapagos Islands and Aldabra (1). To assess how the megafauna extinction impacted body size dynamics in tortoises, we aimed to investigate the following:

1. How is body size distributed in Testudinidae?2. Are there spatial and temporal differences in tortoise body size?3. What are the general body size trends over time?

Material and Methods●Body size data set:

● Fossil tortoises (n = 398 from literature, 203 localities)

●Extant tortoises:(n = 67 museum specimens, n = 173 from literature)

●Body size distribution●Comparisons:

●Fossil vs. modern●Insular vs. mainland

●Timescale analysis:●Model fits (stasis, unbiased random walk, generalized random walk)

SummaryWe found significant differences in tortoise body size on the spatial and the temporal scale. These results suggest that the extinction of giant continental fossil tortoises drives evolutionary patterns of continental and insular species. Loss of biodiversity is not reflected in these patterns, if the size range does not change significantly.

The significant size difference between modern and fossil tortoises on a global scale and within lineage tendencies on the species level are not reflected as a trend in overall testudinid body size. The wide-spread distribution of testudinids comprising different ecological conditions and discrepancies between continental and insular habitat may contribute to a stationary evolutionary trajectory.

Possible reasons for the extinction of giant tortoises are complex and require further investigation. Direct and indirect anthropogenic influence was abundant and may have affected tortoises similar to mammalian megafauna (2,3). Giant tortoises seem to have a narrow optimal temperature range and climatic fluctuations might have affected tortoise populations (4).

References(1) Rhodin, A. G. J., Thomson, S., Georgalis, G. L., Karl, H.-V., Danilov, I. G., Takahashi, A., de la Fuente, M. S., Bourque, J. R., Delfino, M., Bour, R., Iverson, J. B., Shaffer, B. H., and van Dijk, P. P. (2015). Turtles and tortoises of the world during the rise and global spread of humanity: first checklist and review of extinct Pleistocene and Holocene chelonians. Chelonian Research Monographs, 5(5):1–66.(2) Barnosky, A. D. (2004). Assessing the Causes of Late Pleistocene Extinctions on the Continents. Science, 306(5693):70–75.(3) Sandom, C., Faurby, S., Sandel, B., and Svenning, J.-C. (2014). Global late Quaternary megafauna extinctions linked to humans, not climate change. Proceedings of the RoyalSociety B: Biological Sciences, 281(1787):20133254–20133254.(4) Claude, J., Naksri,W., Boonchai, N., Buffetaut, E., Duangkrayom, J., Laojumpon, C., Jintasakul, Pratueng, Lauprasert, K., and Martin, Jeremy, Suteethorn, Varavudh, Tong, H. (2011). Neogene reptiles of northeastern Thailand and their paleogeographcal significance. Annales de Paléontologie, 97:113–131.

3 Department of Biosciences, Swansea University, Wallace Building, Singleton Park, Swansea SA2 8PP, UK4 Smithsonian Tropical Research Institute, PO Box 2072, Balboa, Panama.

1. Body size is bimodally distributed(large tortoises disappear on the continents)

Results

AcknowledgementsMany thanks to Mark-Oliver Rödel, Frank Tillack and Sonja Rothkugel.

2. Fossil tortoises are larger than modern tortoises.Tortoises are larger on islands.

3. Body size dynamics best described by stasis (no net change of mean body size over time)