Fossil leaves from Lukeino, a 6-million-year-old Formation in the Baringo Basin, Kenya

Thirty-eight dicotyledonous leaf morphotypes and some monocot leaf fragments are described from the Kapcharar, Kabogongoi, Koibo Chepkweny and Inoswa Kamelon localities in the upper third of the Lukeino Formation, Tugen Hills, Baringo Basin (Kenya). The leaves are preserved in fine-grained paper shales and range in length from 9 to 160 mm. Some of the leaves show affinities with extant species in the Burseraceae, Ebenaceae, Euphorbiaceae, Fabaceae, Loganiaceae, Malvaceae and Sapotaceae families that are common in the local flora today. There are compound and simple leaves, mostly entire-margined and with only 10% non-entire margins. A CLAMP analysis of the Kapcharar leaves indicates that the local climate was seasonal, summer wet with 1723 mm mean annual rainfall and with a mean annual temperature of 19.8 °C. The vegetation was a deciduous forest or woodland with open areas nearby. A monocot leaf and two fragments of fern pinnae are also described; they imply locally wetter environments. The flora described here is directly associated with the early hominid Orrorin tugenensis.