Fossil Giraffidae (Mammalia, Artiodactyla) from Lee Adoyta, Ledi-Geraru, and Late Pliocene Dietary Evolution in Giraffids from the Lower Awash Valley, Ethiopia

Abstract

The giraffid fossils recovered from~2.8-2.6 million year old (Ma) sediments from Lee Adoyta, Ledi-Geraru, Ethiopia, are described here. Sivatherium maurusium and Giraffa cf. G. gracilis are the two identified taxa, with the former being more abundant than the latter. We interpret this skew of relative abundance to be of paleoenvironmental significance, as Sivatherium is rare and Giraffa is common in the adjacent, but older sediments of the Hadar Formation at Hadar (~3.4 to 2.95 Ma), which was characterized by wooded and well-watered habitats through most of its sequence. Stable carbon isotope analyses show that Giraffa remained an obligate browser throughout the lower Awash Valley (LAV) sequence while Sivatherium underwent a dietary transition from a browser in the Hadar Formation to a grazer at Lee Adoyta. This dietary shift in Sivatherium reflects local environmental change through time in the LAVas open habitats spread during the late Pliocene. A compilation of isotopic data from other sites in eastern Africa shows that the LAV dietary shift in Sivatherium occurred roughly one million years earlier than in the Turkana Basin, Kenya, reflecting a spatiotemporally staggered expansion of C 4 vegetation across eastern Africa.

New Remains of Camelus grattardi (Mammalia, Camelidae) from the Plio-Pleistocene of Ethiopia and the Phylogeny of the Genus

“…The fossil fauna from the new research area, currently under study, is diverse. The abundance of presumably grazing equids and alcelaphin bovids at MLP suggests a relatively open environment with extensive grass cover, as in the nearby Ledi-Geraru sequence (Rowan et al 2016;Bibi et al 2017;Robinson et al 2017), but is not consistent with the sub-desertic environments favored by extant camels. The camel cranium described here (NME-MLP-1346), as well as the additional isolated teeth and postcranial remains, are all from the Seraitu unit dated to c. 2.5 − 2.9 Ma.…”

Environmental context shapes the relationship between grass consumption and body size in African herbivore communities

“…Following Cerling and others (Cerling et al., 2015; Robinson et al., 2021), we analyzed the δ 13 C enamel ‐equivalent values in the dataset, which included converted δ 13 C hair‐keratin and δ 13 C collagen samples. The relative contributions of C 3 and C 4 plants to diet were then estimated from the δ 13 C enamel values using a dual endpoint mixing model with known C 3 and C 4 plant end member δ 13 C values (Abraham et al., 2019; Cerling et al., 2015; Codron et al., 2007; Rowan et al., 2017):$$$$ {\updelta}^{13}{\mathrm{C}}_{\mathrm{measured}}-\varepsilon ={\updelta}^{13}{{\mathrm{C}}_{\mathrm{C}}}_3\times {f_{\mathrm{C}}}_3+{\updelta}^{13}{{\mathrm{C}}_{\mathrm{C}}}_4\times {f_{\mathrm{C}}}_4, $$$$where $$$ {f_{\mathrm{C}}}_3 $$$ and $$$ {f_{\mathrm{C}}}_4 $$$ correspond to the fractions of C 3 and C 4 plants consumed respectively. We assumed an enrichment factor ɛ of +14.1‰ between diet and tooth enamel, per previous studies (see Cerling & Harris, 1999).…”

“…From these stable isotope data, we were able to calculate local grass dependence for herbivore species in each community. Stable isotope data can be used to reconstruct animal feeding habits so long as dietary functional groups of interest are sufficiently differentiated isotopically (Cerling et al., 2015 ; Codron et al., 2007 ; Rowan et al., 2017 ). In tropical Africa, nearly all low‐elevation (<2000 m) grasses employ the C 4 photosynthetic pathway (Edwards et al., 2010 ), whereas other plant functional groups—trees, shrubs, and forbs—predominantly employ the C 3 photosynthetic pathway (Cerling et al., 2015 ; Codron et al., 2007 ; Rowan et al., 2017 ).…”

“…Stable isotope data can be used to reconstruct animal feeding habits so long as dietary functional groups of interest are sufficiently differentiated isotopically (Cerling et al., 2015 ; Codron et al., 2007 ; Rowan et al., 2017 ). In tropical Africa, nearly all low‐elevation (<2000 m) grasses employ the C 4 photosynthetic pathway (Edwards et al., 2010 ), whereas other plant functional groups—trees, shrubs, and forbs—predominantly employ the C 3 photosynthetic pathway (Cerling et al., 2015 ; Codron et al., 2007 ; Rowan et al., 2017 ). These two photosynthetic pathways fractionate CO 2 differently during the process of carbon fixation, such that C 3 plants have a strongly negative carbon isotopic signature (δ 13 C) relative to atmospheric CO 2 , about −26.6‰ for tropical African C 3 plants, whereas the δ 13 C for C 4 ‐photosynthesizing plants, while still negative, is less extreme, at about −10.0‰ for tropical African C 4 grasses (Ambrose & DeNiro, 1986 ; Cerling et al., 2015 ; Cerling & Harris, 1999 ; Codron et al., 2007 ; Rowan et al., 2017 ).…”

“…In tropical Africa, nearly all low‐elevation (<2000 m) grasses employ the C 4 photosynthetic pathway (Edwards et al., 2010 ), whereas other plant functional groups—trees, shrubs, and forbs—predominantly employ the C 3 photosynthetic pathway (Cerling et al., 2015 ; Codron et al., 2007 ; Rowan et al., 2017 ). These two photosynthetic pathways fractionate CO 2 differently during the process of carbon fixation, such that C 3 plants have a strongly negative carbon isotopic signature (δ 13 C) relative to atmospheric CO 2 , about −26.6‰ for tropical African C 3 plants, whereas the δ 13 C for C 4 ‐photosynthesizing plants, while still negative, is less extreme, at about −10.0‰ for tropical African C 4 grasses (Ambrose & DeNiro, 1986 ; Cerling et al., 2015 ; Cerling & Harris, 1999 ; Codron et al., 2007 ; Rowan et al., 2017 ). The isotopic differences between plant functional groups are preserved in the isotopic composition of the herbivores that consume them (Ambrose & DeNiro, 1986 ; Cerling et al., 2015 ; Cerling & Harris, 1999 ; Rowan et al., 2017 ).…”