Elephants develop wrinkles through both form and function

Elephant trunks have folds and wrinkles, but we don’t know how wrinkles differ between elephant species and how trunks and their wrinkles develop. Adult Asian elephants have significantly more dorsal major trunk wrinkles (~126 ± 25 SD) than African elephants (~83 ± 13 SD). There are more dorsal than ventral major trunk wrinkles and there is a closer wrinkle spacing distally than proximally. Wrinkle numbers differed slightly as a function of trunk-lateralization. MicroCT-imaging revealed a relatively constant thickness of the outer elephant trunk skin, whereas the inner skin parts are thicker between folds than in folds. The trunk shows the greatest fetal length growth of elephant body parts. Trunk wrinkles are added in an early exponential phase, where wrinkles double every 20 days, and a later phase, where wrinkles are added slowly and at a faster rate in Asian compared to African elephants. We suggest wrinkles improve the ability of trunk skin to bend.

Methods
The full methods section is included in both the manuscript and the supplement.