Tracks made by swimming Hippopotami: An example from Koobi Fora (Turkana Basin, Kenya)

- We describe animal tracks at the Koobi Fora (GaJi10; Kenya) footprint site.
- The animal tracks at GaJi10 are predominantly subaqueous.
- They contrast with the terrestrial tracks found at Ileret (FwJj14E).
- We describe the first recorded example of swim tracks made by hippopotami.
- We explore how these tracks may help interpret the swim traces made by dinosaurs.

Here the authors report an ichnological surface close to Koobi Fora (Kenya) dating to 1.4 Ma. The surface is marked by hominin tracks, as well as traces from large animals. A southern excavation of the surface some 70 m from the hominin tracks displays a diverse range of animal track typologies, most of which appear to have been made by a four digit animal moving via punting or bottom walking in a shallow water body. Due to the track morphology and the associated fossil record, the non-hominin tracks are interpreted as being made by hippopotami, potentially including pygmy species or juveniles. The track typologies are interpreted using modern analogue observations of hippopotami sub-aquatic locomotion. This work provides important environmental context for adjacent hominin tracks and provides the first recorded description of fossilized swim tracks made by mammals. The site has implications for the interpretation of swim tracks in the geological record particularly the widespread and controversial tracks made by sauropods and other dinosaurs.