A morphotype catalog and paleoenvironmental interpretations of early Miocene fossil leaves from the Hiwegi Formation, Rusinga Island, Lake Victoria, Kenya

Abstract

Early Miocene deposits on Rusinga Island (Lake Victoria, Kenya) contain an abundance of faunal and floral remains. Despite the attention that has historically been given to the early Miocene fauna from Rusinga Island, little attention has been given to the early Miocene fossil floras and to date no studies have described fossil leaf morphotypes from Rusinga Island. Here, we present a morphotype catalog of fossil leaves collected from the Grit Member of the Hiwegi Formation on Rusinga Island. We describe 14 morphotypes, comprised of 12 dicotyledonous angiosperms and two monocotyledonous angiosperms, as well as two distinct dicotyledonous angiosperm leaf fragments. Characteristics of the flora and sedimentological evidence, coupled with previous research, suggest that the local paleoenvironment was a riparian habitat within a patchwork of woodland and forested biomes in what was likely a warm climate. This work represents an important first step in understanding the early Miocene vegetation of Rusinga Island, and highlights both the need and potential for future research on these early Miocene floras.

The Early Miocene Critical Zone at Karungu, Western Kenya: An Equatorial, Open Habitat with Few Primate Remains

“…We reconstruct the NG15 interval as an open canopy environment, ranging from an open riparian woodland to a wooded grassland biome. This is similar to, though perhaps more open than, environmental reconstructions for the Grit Member and lower Fossil Bed Member of the Hiwegi Formation, which are reconstructed as a patchwork of woodland and forested biomes within a riparian habitat in a warm and highly seasonal climate in which evaporitic conditions were recurrent (Collinson et al, 2009;Conrad et al, 2013;Maxbauer et al, 2013). Likewise, the interpretations for the NG15 interval are considerably different from the paleoenvironmental reconstruction for the Kibanga Member of the Hiwegi Formation, which is reconstructed to be a closed-canopy, tropical seasonal forest (Michel et al, 2014).…”

“…Perhaps the most conspicuous difference between Karungu and the Hiwegi Formation is the rarity of primate taxa at Karungu, in comparison to the relatively common primates found in the Hiwegi Formation. Coupled with evidence for variability in paleoenvironment and paleovegetation through the deposits at Karungu and through the Hiwegi Formation (e.g., this study; Collinson et al, 2009;Maxbauer et al, 2013;Michel et al, 2014;Driese et al, 2016), the differences in the faunal abundance and occurrences between Karungu and Rusinga Island are likely related to true faunal differences, possibly as a result of paleoenvironment differences.…”

“…Additionally, our results, which document differences in the faunal assemblages between surface collections at Ngira and the excavation at NG15, also support the interpretation of multiple paleoenvironments within Ngira. Second, paleoenvironmental interpretations for the Hiwegi Formation on Rusinga Island indicate multiple environments ranging from more open shrubland to riparian woodland to closed-canopy tropical seasonal forest (Collinson et al, 2009;Conrad et al, 2013;Maxbauer et al, 2013;Michel et al, 2014). Third, the paleoenvironmental reconstructions for nearly every Critical Zone component reconstructed for NG15 are different from most recent environmental and climatic reconstructions of the Hiwegi Formation.…”

“…Third, the paleoenvironmental reconstructions for nearly every Critical Zone component reconstructed for NG15 are different from most recent environmental and climatic reconstructions of the Hiwegi Formation. While the stratigraphy at Ngira consists of interbedded fluvial and lacustrine strata , sedimentation in the Hiwegi Formation is a mixture of fluvial, palustrine, and primary and reworked volcaniclastic material (e.g., ash fallout and lahars; Bestland and Krull, 1999;Maxbauer et al, 2013;Michel et al, 2014). This indicates that there were substantial differences in physical sedimentary environments between Karungu and the Hiwegi Formation.…”

New Miocene Carnivora (Mammalia) from Moruorot and Kalodirr, Kenya

“…Overall, however, Early Miocene records of carnivorans in the Turkana Basin are scarce (Savage, 1965;Anyonge, 1991;Werdelin and Peigné, 2010;Leakey et al, 2011;, and little material has been described. Currently known carnivorans from West Turkana include representatives of genera and species also present elsewhere, particularly in the Hiwegi Formation of Rusinga Island, western Kenya (Collinson et al, 2009;Maxbauer et al, 2013) (Figure 2 1). Rusinga has a time-averaged collection sampling different localities ranging approximately between 20 Ma and 17 Ma (Peppe et al, 2017).…”