Search

We report on the Late Pleistocene (36–12 ka) mammals from Kibogo in the Nyanza Rift of western Kenya, providing (1) a systematic description of the mammal remains, (2) an assessment of their paleoenvironmental implications, and (3) an analysis of the biogeographic implications of non-analog species associations. Kibogo has yielded one of the largest paleontological assemblages from the Late Pleistocene of eastern Africa, and it is dominated by grassland ungulates (e.g., equids and alcelaphin antelopes), including an assortment of extralimital (e.g., Equus grevyi, Ceratotherium simum, Redunca arundinum) and extinct species (Syncerus antiquus, Damaliscus hypsodon, Megalotragus sp.). The composition of the fauna, in conjunction with the soils and topography of the region, indicate the local presence of edaphic grassland situated within a broader environment that was substantially grassier and likely drier than at present. In contrast to non-analog faunas from higher latitudes (e.g., North America and western Eurasia), the climatic niches of non-analog species associations strongly overlap, indicating that non-analog climate regimes during the Late Pleistocene of eastern Africa are not necessary to account for the former association of presently allopatric species. The Kibogo faunas add to a growing body of evidence implying that the composition of present-day African herbivore communities is distinct from those of the geologically recent past. [ABSTRACT FROM AUTHOR]

Ecometric analysis involves the examination of quantifiable functional traits across the taxa in a biotic community. Well-documented relationships between certain functional traits and environmental gradients in the present provide the empirical framework for a large body of research that uses ecometrics to reconstruct environments in the fossil record. In current applications of the technique, the taxa present in a fossil assemblage are summarized using the mean value of an environmentally informative trait. This study explores some of the quantitative pitfalls inherent to this approach. Through analysis of dental crown height—a trait that is widely used to infer paleo-precipitation—of Late Pleistocene ungulate assemblages from the Lake Victoria Basin in western Kenya, we illustrate how ecometric means vary as a function of sample size. Sampling artifacts have the potential to bias ecometric means, and the environmental inferences derived from them, whenever there is a non-random distribution of traits across the species abundance distribution (e.g., if abundant taxa have different traits than rare taxa). This sampling issue also means that the degree of analytical precision implied by quantitative paleoenvironmental reconstructions (e.g., annual precipitation at time X was 500 mm/yr) derived from ecometrics may be unwarranted. We recommend that analytical approaches be modified to circumvent these problems and explore three potential solutions: (1) specimen-based rarefaction, (2) coverage-based rarefaction, and (3) weighting ecometric means by taxonomic abundances. Of these, only the latter is robust to variation in sampling effort. Because abundance data are not always available and are potentially unreliable, we outline alternative approaches that could be implemented to contend with sample bias. • Ecometric means can vary as a function of fossil assemblage sample size. • This occurs when traits are not random across the species abundance distribution. • Paleoenvironmental inferences derived from ecometric means can be skewed. • Weighting ecometric means by taxonomic abundances overcomes sampling issues. • Quantitative reconstructions of past climate variables are not recommended. [ABSTRACT FROM AUTHOR]

Grévy's zebra (Equus grevyi) has been reported from fossil sites spanning the past 2.3 Myr and covering a wide geographic range. However, no currently published reports dating to >200 ka can be confidently attributed to E. grevyi , with most specimens better allocated to another taxon or lacking diagnostic characteristics aligning them with E. grevyi to the exclusion of other large Equus species such as E. oldowayensis. This leaves the origin of Grévy's zebra unresolved. Here, we describe a largely complete cranium of a large mare from the Kapthurin Formation in Kenya's Baringo Basin that represents the first definitive appearance of E. grevyi at 547.0–392.6 ka. This cranium falls within the range of variation for recent E. grevyi and is morphologically distinct from all other fossil and extant zebras. The new Kapthurin specimen has implications for the complex evolutionary history of large zebras. Furthermore, it provides insights into the mechanisms underpinning the expanded range of Grévy's zebra during the Pleistocene. Based on species distribution modeling and a multivariate analysis of its climate niche, we argue that the wide fossil distribution of E. grevyi may have had little to do with Pleistocene aridity as previously argued. Instead, the range contraction of Grévy's zebra may have been driven by competition with plains zebra (E. quagga) after the northward expansion of the latter species. • An equid cranium is described from the Kapthurin Formation of Kenya. • This cranium represents the first appearance of Equus grevyi in the fossil record. • Equus grevyi had an expanded range during the Middle to Late Pleistocene. • The northward expansion of Equus quagga may explain local extirpation of E. grevyi. [ABSTRACT FROM AUTHOR]