Test of climate-leaf physiognomy regression models, their application to two Miocene floras from Kenya, and super(40)Ar/ super(39)Ar dating of the Late Miocene Kapturo site

To test multiple regression models developed to predict seven variables of climate from leaf margin and size characters, leaf character data were collected from modern woodland and rainforest plant communities in Uganda. These localities were chosen for their structural similarity to two fossil sites for which climate values were desired. The test indicated that for these communities, the model accurately predicts mean annual temperature. However, the multiple regression models overestimate seasonality of temperature and mean annual and seasonal precipitation amounts for the two modern communities. Reasons for the models' inaccuracies may include, no African analog in the non-African database on which the model is based, too much intraspecific variability in leaf size (an important character in precipitation models), and relationships between leaf form and climate that may not be well defined by multiple regression. Mean annual temperatures were reconstructed for two Miocene paleobotanical localities from the Tugen Hills of the eastern rift valley, Kenya, using leaf form data (primarily margin characters). The results indicate that mean annual temperatures at Kabarsero (12.6 Ma), and Kapturo (6.7-7.2 Ma), were essentially equivalent to temperatures at those localities today and differed little from one another. The Kapturo paleofloral assemblage is a deciduous woodland interpreted as indicating less available or more seasonal moisture than the Kabarsero paleofloral assemblage, a wet forest with West African floral affinities. Laser-fusion super(40)Ar/ super(39)Ar dating of volcanic materials at Kapturo provides the first control of this paleoflora, bracketed by a 7.2 Ma trachyte at the base of the sedimentary sequence, and an age of 6.7 Ma on a reworked tuff overlying the fossiliferous horizon. The chronologic data places the paleofloral assemblage in stratigraphic context relative to other Tugen Hills units containing paleofloras and abundant vertebrate remains including hominoids.