Potential evolutionary body size reduction in a Malagasy primate (Propithecus verreauxi) in response to human size-selective hunting pressure

Objectives: The Holocene arrival of humans on Madagascar precipitated major changes to the island's biodiversity. The now-extinct, endemic “subfossil” megafauna of Madagascar were likely hunted by early human inhabitants. Perhaps in part due to preferential hunting of larger prey, no surviving endemic species on Madagascar is >10 kg. Moreover, some subfossil bones of extant lemurs are considerably larger than those of the modern members of their species, but subfossil versus modern locale differences for the comparisons conducted to date lead to uncertainty about whether these size differences reflect in situ change or pre-existing ecogeographic variation. Here, we revisited this question with samples from nearby locales. Materials and Methods: We used high-resolution 3D scan data to conduct comparative morphological analyses of subfossil and modern skeletal remains of one of the larger extant lemurs, Verreaux's sifakas (Propithecus verreauxi) from subfossil and modern sites only ~10 km apart: Taolambiby (bones dated to 725–560—1075–955 cal. years before present) and Beza Mahafaly Special Reserve, respectively. Results: The mean aggregate score for all subfossil elements (n = 12; 0.089 ± 0.117) is significantly greater than that for the modern individuals (n = 31; 0.009 ± 0.045; t-test; p = 0.039). We found that the average subfossil sifaka bone is ~9% larger than that of modern sifakas (permutation test p = 0.037). Discussion: We cannot yet conclude whether this size difference reflects evolutionary change or an archaeological aggregation/taphonomic process. However, if this is a case of phyletic dwarfism in response to human size-selective harvesting pressures then the estimated rate of change is greater than those previously calculated for other archaeological cases of this phenomenon.