Why elephant have trunks and giraffe long tongues: how plants shape large herbivore mouth morphology

Abstract

Abstract Pretorius, Y., de Boer, W.F., Kortekaas, K., van Wijngaarden, M., Grant, R.C., Kohi, E.M., Mwakiwa, E., Slotow, R., Prins, H.H.T. 2015. Why elephant have trunks and giraffe long tongues: how plants shape large herbivore mouth morphology. -Acta Zoologica (Stockholm) 00: 000-000. We investigated whether mass and morphological spatial patterns in plants possibly induced the development of enlarged soft mouth parts in especially megaherbivores. We used power functions and geometric principles to explore allometric relationships of both morphological and foraging characteristics of mammalian herbivores in the South African savannah, covering a body size range of more than three orders magnitude. Our results show that, although intradental mouth volume scaled to a power slightly less than one to body mass, actual bite volume, as measured in the field, scaled to body mass with a factor closer to 1.75. However, when including the volume added to intradental mouth volume by soft mouth parts, such as tongue and lips (or trunks in elephant), mouth volume scaled linearly with actual bite volume and in a similar fashion as actual bite volume to body size. Bite mass and bite leaf mass scaled linearly with body size. We conclude that these scaling relationships indicate that large herbivores use their enlarged soft mouth parts to not only increase bite volume and thereby bite mass, but also select soft plant parts and thereby increase the leaf mass fraction per bite