Isotopic insights into the Early Acheulean (1.95 Ma-1.66 Ma) high-elevation paleoenvironments at Melka Kunture (Upper Awash, Ethiopia)

doi:10.21203/rs.3.rs-2155280/v1

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Isotopic insights into the Early Acheulean (1.95 Ma-1.66 Ma) high-elevation paleoenvironments at Melka Kunture (Upper Awash, Ethiopia)

https://doi.org/10.21203/rs.3.rs-2155280/v1

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In this paper, we present carbon and oxygen stable isotope analysis of fauna tooth enamel from Garba IVD (~1.95 Ma) and Gombore IB (~1.66 Ma), two Early Acheulean sites of Melka Kunture (Upper Awash, Ethiopia) and discuss faunal taxonomy and fossil pollen. Our aim is to infer the diet, habitat, and environment at both sites and provide a broader paleoecological reconstruction. During the Pleistocene, the vegetation of the highlands of Ethiopia belonged to the “Dry evergreen Afromontane Forest and grassland complex”, distinct from the savanna of lower elevations in East Africa.

Our carbon isotopic results indicate that all the analyzed faunal taxa were grazers, consuming C₄ grasses, while oxygen isotopic results clearly discriminate the taxa according to their semi-aquatic or terrestrial habitats. These results are consistent with the analysis of the faunal assemblages and the palynological results, suggesting extended mountain grasslands in the landscape at Garba IVD. In contrast, the carbon isotopic results do not totally agree with the pollen paleoenvironmental reconstruction at Gombore IB, where the open vegetation was interrupted by forests and bushy vegetation. Stable isotopes and pollen data provide different outcomes (feeding strategies vs. nearby plants) and have different temporal and spatial resolutions. This is relevant when reconstructing past environments by exclusively using independent proxies. Furthermore, isotopic comparisons with other East African archaeological sites of the Lower Pleistocene age indicate that all the analyzed taxa fed on C₄ grasses, and that their dietary strategies were not affected by differences linked to various elevations.

Melka Kunture

Early Acheulean

stable isotopes

paleodiet

paleoenvironment

paleoecology

Multiple proxies such as stable isotopes, dental wear, faunal abundance and taxonomy, fossil pollen and phytolith analysis, geomorphological studies, skeletal morphometrics, and ichnology provide insights on mammalian diet, habitat, environment, and behavior that concur with providing a wealth of information for ancient ecological reconstructions.

The present study couples and crosschecks faunal taxonomy, fossil pollen, and new stable isotope analysis (¹³C, ¹⁸O) on faunal teeth from Early Acheulean Level D at Garba IV (Garba IVD) and level B at Gombore I (Gombore IB), in order to investigate the related paleoecology at ~ 1.95 Ma and ~ 1.66 Ma. The sites are part of the Melka Kunture cluster of prehistoric deposits, located on the highlands of Ethiopia at ~ 2000–2200 m above sea level. Due to the elevation, the vegetation belonged to the “Afromontane complex” (Bonnefille et al., 2018) which greatly differs from the savanna vegetation of the Pleistocene African sites at lower altitudes.

Pollen analysis documents open vegetation with extended high-elevation grasslands in the paleolandscape of Garba IVD, while Gombore IB was marked by a rather forested mountain environment (Bonnefille et al., 2018). The taxonomic composition of the fauna did not significantly differ between the two sites, indicating a preference for open habitats (Geraads et al., 2004, 2022). Given the known faunal assemblages and paleoenvironmental differences between the two layers, our aim is to determine if and how this is reflected in the carbon and oxygen stable isotope composition of the fauna tooth enamel. Accordingly, the objectives of this paper are 1) to provide information on the diet and habitat of the fossil fauna; 2) to assess whether the different local vegetation (grassland and forest) influenced the dietary selection of Pleistocene animals; 3) to refine the paleoecological characteristics of both Early Acheulean archaeological levels; 4) to evaluate the outcome of different approaches in paleoenvironment reconstruction.

1.1 Archaeological background

Garba IVD and Gombore IB are archaeological layers of the multi-stratified Garba IV and Gombore I sites within the Melka Kunture deposits (8° N, 38° E). They are located about 50 km southwest of Addis Ababa, on the western shoulder of the Main Ethiopian Rift, between 2000 and 2200 m a.s.l. (Fig. 1). Both are on the right bank of the Upper Awash River, at a short geographic and stratigraphic distance from each other (Chavaillon and Piperno, 2004; Piperno et al., 2009; Mussi et al., 2022). ⁴⁰Ar/³⁹Ar analysis formerly suggested an age of ~ 1.6 Ma for Garba IVD, which stratigraphically lies on the “Grazia tuff” (< 1.719 ± 0.199 Ma). Gombore IB has been estimated to be close in age based on geo-stratigraphic correlations (Raynal and Kieffer, 2004). Recent magnetostratigraphic analyses established an older chronology, assessing Garba IVD at ~ 1.95 Ma and Gombore IB at ~ 1.66 Ma (Perini et al., 2021). Both levels yielded a high-density distribution of Early Acheulean lithic artifacts, faunal remains, and unworked pebbles (Gallotti, 2013; Gallotti and Mussi, 2017, 2018; Mussi et al., 2021). A left distal humerus (Gombore IB-7594) attributed to Homo cf. erectus was found in situ at Gombore IB (Di Vincenzo et al., 2015). An H. erectus child mandible was also discovered at Garba IV in level E, associated with an Oldowan technocomplex. At ~ 2 Ma, it predates the overlying level Garba IVD (Le Cabec et al., 2021; Perini et al., 2021).

1.2 The faunal remains

The fauna recovered from Garba IVD is dominated by large hippos (Hippopotamus cf. amphibius), grazing bovids (mostly Alcelaphini, Connochaetes gentryi leptoceras, Damaliscus strepsiceras, but also Antilopini, with a Gazella close to G. rufifrons, and Antidorcas) and equids (Hipparion s.l.). The suids include Kolpochoerus and Metridiochoerus. The gelada baboon Theropithecus, a rare genus at Melka Kunture, is represented by a single specimen (Geraads et al., 2004). The same open country alcelaphins dominate the mammalian collection of both sites; it also includes two species of equids, three species of suids, and two hippos (H. cf. amphibius, and a dwarf hippo, resembling H. cf. aethiopicus). Both faunal assemblages point to a preference for open habitats (Table 1) (Mussi et al., in press; Geraads et al., 2022).

Table 1

Distribution of the vertebrate *taxa* at Garba IVD and Gombore IB (Geraads et al., 2022)
	Garba IVD	Gombore IB
Theropithecus oswaldi	+
Elephas recki recki	cf.	cf.
Stylohipparion sp.	+	+
Equus cf. capensis	+
Equus cf. stenonis	+	+
Equus sp.	+	+
Hippopotamus cf. amphibius	+	+
Hippopotamus cf. aethiopicus		+
Kolpochoerus majus	+
Kolpochoerus cf. olduvaiensis		+
Metridiochoerus cf. andrewsi	+	sp.
Metridiochoerus modestus	cf.
Giraffa cf. camelopardalis	+
Sivatherium maurusium	+
P. turkanensis brachyceras	+	sp.
Kobus sp. (small).	+
Connochaetes gentryi leptoceras	+	cf.
Damaliscus strepsiceras	+	+
Damaliscus cf. korrigum	+
Parmularius cf. angusticornis	+
Gazella cf. rufifrons	+	sp.
Antidorcas cf. recki	+
Arvicanthis sp.	+
Tachyoryctes konjitae	+
Hystrix sp.	+
Cygnus sp.	+
Crocodylus sp.	+	+
Chelonia indet.	+

1.3 The paleobotanical data

The pollen samples collected at Garba IVD (samples G133 and G393 in Bonnefille et al., 2018) record extensive development of high-elevation grasslands, evidenced by a high percentage of grass pollens (Plantago and various species of Asteraceae) and the shrub Myrsine africana. The assemblages also include some Podocarpus and Dodonaea viscosa pollen, pointing to limited wooded vegetation either locally or at a distance from the site since these pollen types are known to be easily dispersed. In contrast, the pollen sample from Gombore IB (samples Gomb IB in Bonnefille et al., 2018) records a high amount of Juniperus (> 20%) and more species of present-day mountain forest (such as Podocarpus, Olea, and Myrica). As Juniperus disperses pollen not far from the tree, a juniper-dominated forest was developing nearby. The finding of a fossilized forest climber (liana) (Chavaillon and Koeniguer, 1970) also confirms this environmental interpretation. However, the large percentage of grass pollen of Poaceae (> 63%) attests that grazing land was also available. The open vegetation was interrupted by the forest, probably near the river (Fig. 2) (Bonnefille et al., 2018).

1.4 Carbon and oxygen stable isotopes analysis in tooth enamel

The stable isotope analysis of carbon and oxygen isotopic abundances in tooth enamel provides direct evidence of the dietary patterns, ecology, and habitat since the isotopic signal is related to the plants consumed and the water ingested during the formation of the analyzed tissue. Tooth enamel is the most suitable fossilized material for preserving stable isotopic signatures since it is almost entirely inorganic (hydroxyapatite) and less susceptible to alteration due to diagenesis (Wang and Cerling, 1994; Schoeninger et al., 2003). The stable isotopic results are typically expressed with the following standard δ-notation: X = [(R_sample/R_standard)-1]∗1000, where X is referred to as δ¹³C, and δ¹⁸O values and R represents ¹³C/¹²C or ¹⁸O/¹⁶O, respectively.

The carbon isotope ratio in tooth enamel is an average of the diet related to the plants eaten by the animals. Terrestrial plants are generally divided into C₃ and C₄ plants according to their different photosynthesis pathways, leading to different carbon isotopic fractionation during the CO₂ fixation processes (Edwards and Walker, 1983). The C₃ photosynthetic pathway (Calvin-Benson cycle) occurs in all trees and bushes, temperate shrubs, and grasses adapted to cool climates and high altitudes. The C₃ plants have an average δ¹³C value of -27‰ (range from − 35‰ to -22‰). The C₄ photosynthetic pathway (Hatch-Slack cycle) occurs in grasses, sedges, and herbs typical of drier and warmer environments. The C₄ plants have δ¹³C values ranging from − 19‰ to -9‰, showing a mean of -13‰ (Smith and Epstein, 1971; O’Leary, 1988). In East Africa, stable carbon isotopes values allow distinguishing between browser (≤-8‰), mixed feeders (≥-8‰ to ≤ 1‰), and grazers (≥ 1‰) feeding on leaves (C₃ plants), leaves, and grasses (C₃ and C₄ plants), and grass (C₄ plants), respectively. Accordingly, the abundance of C₄ plants suggests a relatively open environment, while C₃ plants point to more woody vegetation under more humid climatic conditions (Farquhar et al., 1989; Cerling and Harris, 1999).

The oxygen isotope composition in mammalian tooth enamel reflects the isotopic composition of the body water, which is determined by the drinking water and ingested food. Due to evaporation, the δ¹⁸O values in plant leaves are higher than those in meteoric water. It means that the herbivores eat leaves with higher oxygen isotopic values than those drinking meteoric water (Kohn, 1996; Kohn et al., 1998), allowing to distinguish the browsers from the grazers. In addition, δ¹⁸O values will enable us to determine the so-called “obligate drinkers,” who obtain water from the rivers or lakes (δ¹⁸O of meteoric water), from the other “non-obligate drinkers” that get most of their water from leaves, showing higher δ¹⁸O values. The oxygen isotopic composition can also be affected by habitat differences: for semi-aquatic mammals such as hippos, the stable oxygen isotopic composition is depleted in ¹⁸O compared to that of terrestrial herbivores (Bocherens et al., 1996; Clementz and Koch, 2001; Clementz et al., 2008; Harris et al., 2008). Furthermore, many other aspects can play a relevant role in the variation of oxygen isotope composition, such as precipitation, continentality, seasonality, latitude, and altitude (Pederzani and Britton, 2019).

We analyzed the carbon and oxygen isotopic composition of 18 fossil teeth (5 carbonate samples from Garba IVD and 13 carbonate samples from Gombore IB) (Fig. 3, 4). We further added 9 samples published by Bocherens et al. (1996) (6 samples from Garba IVD and 3 samples from Gombore IB). Collectively, we discuss 27 bulk enamel samples (Table 2) from fossil teeth taxonomically identified by one of us (D.G.) (Geraads et al., 2004, 2022). The specimens include Artiodactyla (Hippopotamidae, Bovidae, Suidae) and Perissodactyla (Equidae) (Table S1). The enamel samples were collected in November 2019 at the National Museum of Ethiopia (Addis Ababa), where the paleontological collection was stored. Each specimen is labeled with the acronym of the archaeological area (MLK = Melka Kunture), followed by a progressive number (i.e., MLK-15, MLK 16, etc.). Briefly, 12–15 mg of enamel was pretreated with NaOCl followed by buffer acetic acid-calcium acetate; then 2.5-3 mg of powdered enamel was analyzed using a MultiFlow-Geo interface with the Elementar IsoPrime 100 IRMS. The stable isotopic results are typically expressed using the standard δ-notation: X = [(R_sample/R_standard)-1]∗1000, where X is referred to as δ¹³C, and δ¹⁸O values and R represents ¹³C/¹²C or ¹⁸O/¹⁶O, respectively. All laboratory activities were carried out at the Biogeology working group (Department of Geosciences, University of Tübingen), following the internal protocol for the preparation and isotopic analysis of archaeological teeth (Bocherens et al., 1996) (Supplementary A and B).

Table 2

Distribution of the analyzed enamel samples from Garba IVD and Gombore IB
	Garba IVD	Gombore IB	Total
Hippopotamidae	8	6	15
Bovidae	1	5	6
Equidae	1	1	2
Suidae	1	4	4
Total	11	16	27

3.1 The δ¹³C and δ¹⁸O values from Garba IVD

The δ¹³C values of tooth enamel samples from Garba IVD ranged from − 4.7‰ to + 2.7‰, covering the range of mixed C₃-C₄ and C₄ plant consumers (Table S1) (Fig. 5). Notably, the δ¹³C values of hippopotamids (n = 8) varied from − 0.8‰ to + 2.6‰ (median: +0.5‰), indicating a C₄ diet. Only a single δ¹³C value (-4.7‰) was depleted compared with the other values, indicating a mixed C₃-C₄ diet for this hippo. A bovid (n = 1), equid (n = 1), and suid (n = 1) consumed C₄ grasses with values of + 1.9‰, + 2.7‰, and + 0.6‰, respectively. The δ¹⁸O values ranged from + 21.2‰ to + 31.7‰. The oxygen isotopic values were more depleted for the hippos (median: +25.2‰) than for the fully terrestrial animals such as suids (+ 25.9‰), equids (+ 30.9‰), and bovids (+ 31.7‰), reflecting distinct habitats (Mann-Whitney U-test, p = 0.0294).

3.2 The δ¹³C and δ¹⁸O values from Gombore IB

At Gombore IB, the δ¹³C values of tooth enamel ranged from − 2.3‰ to + 3.3‰, suggesting a pure C₄ diet for herbivores (Table S1) (Fig. 6). The hippopotamid (n = 6) δ¹³C values ranged from − 1.2‰ to + 0.8‰ (median: -0.3‰), and the bovids (n = 5) had a δ¹³C median of + 2.9‰, with carbon isotopic values from − 0.6‰ to + 3.3‰. The δ¹³C values of suids (n = 4) varied from − 2.3‰ to + 1.2‰ (median: +0.1‰), while the δ¹³C value of the equid sample (Hipparion) was + 0.1‰. The δ¹⁸O isotopic results for all analyzed mammals ranged from + 19.2‰ to + 33.1‰. As for the Garba IVD, the hippopotamids had lower δ¹⁸O values (median: +23.7‰), whereas those of bovids (median: +27.7‰), equids (+ 26.5‰), and suids (median: +27.5‰) were more positive, consistent with the expected difference between aquatic and terrestrial habitats (Mann-Whitney U-test, p = 0.0169).

4.1 Dietary and paleoenvironmental reconstruction

The carbon and oxygen isotopic results reflect ecological conditions based on faunal lifestyles and preferred habitats. This is evidenced by the δ¹⁸O values from Garba IVD (~ 1.95 Ma) and Gombore IB (~ 1.66 Ma), which discriminate the taxa according to their semi-aquatic or terrestrial habitats. The δ¹³C values from both sites/levels suggest that all the analyzed faunal taxa were grazing and fed mostly on C₄ grasses. Only a hippo δ¹³C value from Garba IVD has a mixed C₃-C₄ isotopic signal, interpreted as consuming C₃ cool-season grass. Indeed, Melka Kunture is located at the elevation where grasslands would include mostly C₄ grasses but also some C₃ ones that become dominant above 3000 m of elevation (Tieszen et al., 1979).

The results are consistent with the faunal taxonomy that suggests environments characterized by open grasslands (Geraads et al., 2022). Our carbon isotopic data also agree with the palynological results at Garba IVD, where extended mountain grasslands are documented. In contrast, isotopic results do not totally agree with the paleoenvironmental reconstruction by fossil pollen at Gombore IB, where the open landscape was interrupted by forests and bushy woodland for which the taxonomic determination of the fossil fauna and isotopic analyses provide no evidence. The possibility that the C₄ isotopic signal could indicate the movement of fossil fauna from lower to higher elevation grasslands and woodlands is in contrast with the development of endemic animal species and subspecies, such as Damaliscus strepsiceras and Connochaetes gentryi leptoceras, pointing to some degree of isolation of the Ethiopian highlands (Mussi et al., in press).

A distinct environment at Garba IVD and Gombore IB is not surprising, given the different ages. The wet-dry climate variability on the timescale of 20,000 years of processional monsoon cycles could easily cause a significant change in vegetation cover (Bonnefille and Riollet, 1988). We underline that at Melka Kunture, even in the relatively open landscape of Garba IVD, grassland and wooded areas were always available in various percentages at a short distance. The animals were likely to be selective when feeding. Their diet was possibly based on preferred grasses rather than immediately available vegetation. Modern hippos are notably known to regularly travel some kilometers to forage at night on preferred grass spots, whenever those are not available close to the body of water where they spend the daytime (Eltringham, 1999). At Melka Kunture, there is direct evidence of a hippo trail produced by H. cf. amphibius, which predates 0.7 Ma (Altamura et al., 2017).

While reconstructing the paleoenvironment, stable isotope and pollen analyses are better understood as complementary proxies. Stable isotope values of the tooth enamel record the time-averaged over a long period (several months to years), when the analyzed tooth part was still growing in the jaw of the individuals, not the time of death. They are also related to each specimen's feeding strategies and behavior, including the selection of the preferred vegetation. Fossil pollen analysis registers local plants, wind-pollinated plants, and plant species located at some distance from the deposit. Thus, isotopes and pollen record different temporal and spatial aspects.

4.2 The δ¹³C and δ¹⁸O comparison from tooth enamel in East Africa

We selected 284 isotopic results (¹³C, ¹⁸O) from the fauna tooth enamel of three East African archaeological areas of the Lower Pleistocene age (Olduvai Gorge, Shungura Formation, and several sites of the Lake Turkana Basin) in order to compare our results and interpretations in a broader regional perspective. Collectively, we discuss 308 isotopic results, including data from Melka Kunture. The selected archaeological sites are located at medium and low elevations, between ~ 1400 and 336 m a.s.l., while Melka Kunture is the only site at ~ 2000 m a.s.l. The isotopic dataset includes four fauna family groups: Hippopotamidae, Bovidae, Equidae, and Suidae. Only values from specimens between ~ 2.0-1.95 Ma and ~ 1.6 Ma were selected (Table S3).

Hippopotamidae. The fossil hippos (n = 59) from Melka Kunture, Shungura Formation, Lake Turkana Basin, and Olduvai Gorge belong to Hippopotamus cf. amphibius, Hippopotamus gorgops, aff. Hippopotamus aethiopicus, aff. Hippopotamus karumensis and other hippopotamids. The median value of δ¹³C was − 0.3‰ with minimum and maximum values of − 7.2‰ and + 2.6‰, respectively. The carbon isotopic data suggest that the hippopotamids had a C₄-dominated diet. However, some δ¹³C values from Shungura Formation and Melka Kunture point to a mixed C₃-C₄ diet. This is consistent with other isotopic studies (Morgan et al., 1994; Bocherens et al., 1996; Zazzo et al., 2000; Cerling et al., 2003; Boisserie et al., 2005; Levin et al., 2008), showing opportunistic feeding strategies for hippos, which sampled the available vegetation within long and short distances from their source of aquatic shelter. The δ¹⁸O values show a median of + 26.5‰ with a range of + 20‰ to + 30.5‰ (Bocherens et al., 1996; Harris et al., 2008; van der Merwe, 2013; Ascari et al., 2018; Rivals et al., 2018; Uno et al., 2018; Negash et al., 2020).

We note that the hippopotamids from Melka Kunture show lower δ¹⁸O values (median: +24.6‰) than those of mid- and low-altitude sites (median: +27‰). This is related to the altitude effect. The water condensation that continues throughout a storm, along a mountain slope, or across a continent prefers the heavier isotope, and the remaining vapor becomes depleted in the heavy isotope. Thus, the clouds remove H₂¹⁸O in the form of rain from cloud moisture. This results in comparatively low δ¹⁸O values in high-altitude precipitation and higher δ¹⁸O values in low-altitude precipitation (Dansgaard, 1964; Gat, 2000; Pederzani and Britton, 2019). This could also have implications for the temperature, indicating colder climatic conditions in the mountain environment at Melka Kunture. Nowadays, in Ethiopia, the "big rains" (June-September) are sourced by moist southwesterlies and westerlies from the Atlantic Ocean, while the shorter rainy season (March-May) is associated with the southeastern monsoon from the Indian Ocean (Griffiths, 1972; Gamachu, 1977; Vizy and Cook, 2003; Bedaso and Wu, 2021). Vuille et al., (2005) recorded through isotopic data and model simulations that δ¹⁸O in East African rainfall is closely related to the Indian Ocean Zonal Mode (IOZM). The Boneja meteorological station (20 km north of Melka Kunture) recorded a mean annual rainfall of 860 mm. During 1974–2012, a wide rainfall variability was recorded with a minimum value of 388 mm, and a maximum of 1419 mm (Bonnefille et al., 2018). The maximum temperature is 17.2°C, and the minimum is 8°C (Fekadu, 2012).

Bovidae. This group comprises several bovids (n = 158) of Alcelaphini, Antilopini, Bovini, Hippotragini, Reduncini, Tragelaphini, and other bovids from Melka Kunture, Shungura Formation, and Olduvai. Collectively, the δ¹³C values (median = + 0.5‰) suggest that the diverse tribes of bovids had a wide range of feeding strategies, including a significant C4 component in their diet but also feeding by mixed C₃-C₄ resources. Some bovids from Shungura Formation and Olduvai Gorge show lower δ¹³C values, indicating a mixed C₃-C₄ diet (Bocherens et al., 1996; van der Merwe, 2013; Ascari et al., 2018; Rivals et al., 2018; Uno et al., 2018; Negash et al., 2020). The δ¹⁸O values record a wide range, reflecting the different drinking habits of these bovid tribes. As with the hippos, the oxygen isotopic results from Melka Kunture were lower than in the other localities.

Equidae. The fossil equids (n = 33) from Melka Kunture and Olduvai Gorge are Equus olduwayensis, Hipparion, and other equids. The δ¹³C values range between − 1.8‰ and + 3‰ (median = + 0.8‰), indicating a dominant C₄ diet. The δ¹⁸O values are homogeneous with a median value of + 30.6‰ and values ranging from + 25.3‰ to + 31.9‰ (Bocherens et al., 1996; van der Merwe, 2013; Rivals et al., 2018; Uno et al., 2018).

Suidae. The suid group (n = 61) consists of Kolpochoerus, Kolpochoerus afarensis, Kolpochaerus limnetes, Kolpochoerus majus, Kolpochoerus cf. olduvaiensis, Kolpochoerus paiceae, Metridiochoerus, Metridiochoerus compactus, Notochoerus, Phacochoerus modestus, and other suids from Melka Kunture, Shungura Formation, and Olduvai Gorge. The δ¹³C values indicate diets dominated by C₄ plants for all genera, ranging from − 3.1‰ to + 1.2‰ (median = -0.3‰). In contrast, only some δ¹³C values were lower, indicating a mixed C₃-C₄ feeding strategy. The δ¹⁸O values have a median of + 29.4‰, ranging from + 23.6‰ to + 37.1‰ (van der Merwe, 2013; Ascari et al., 2018; Rivals et al., 2018; Uno et al., 2018; Negash et al., 2020).

Collectively, the isotopic comparisons indicate that Hippopotamidae, Bovidae, Equidae, and Suidae were grazing and fed primarily on C₄ grasses, likely reflecting predominantly open vegetation at low, medium, and high altitudes. Accordingly, C₄ grasses were an important part of the mammalian diet, and the ungulate's feeding strategies were not affected by differences linked to various elevations. Moreover, the oxygen isotopic data of Melka Kunture’s hippos point to a cooler temperature than elsewhere at lower elevations.

The analysis of stable isotopes on faunal tooth enamel from the Early Acheulean layers of Garba IVD (~ 1.95 Ma) and Gombore IB (~ 1.66 Ma) were used to reconstruct the diet and habitat of the Pleistocene fauna. The carbon isotopic data indicate a C₄-dominated diet for all the analyzed taxa. The oxygen isotopic data show a clear distinction between semi-aquatic and terrestrial habitats. Our results are consistent with the faunal analysis, indicating an extended C₄ grassland in the vegetation. However, at Garba IVD, pollen documents a mountain grassland, whereas a relatively forested environment is recorded at Gombore IB. This complementary information helps track the feeding strategies of mammals. The paleovegetation changed over time, while isotopic studies of the fossil fauna show constant feeding habits on C₄ plants.

Comparisons with isotopic results from East African sites do not allow to identify of variations in feeding strategies at high, medium, and low altitudes, even though Melka Kunture recorded the “Dry evergreen Afromontane Forest and grassland complex”, a distinct mountain vegetation that does not include any of the species of the lowland savannas. At Melka Kunture itself, while the vegetation changed over approximately 300,000 years, between ~ 1.95 Ma (Garba IVD) and ~ 1.66 Ma (Gombore IB), the dietary strategies of the fauna were scarcely modified, which has implications for environmental reconstructions based exclusively on the fauna isotopic studies.

Reconstructing the environment using more than a single method of analysis produces sounder results, which is especially important if the development of grasslands and open landscapes is used as a proxy for aridification. At Melka Kunture, H. erectus definitely made Early Acheulean technocomplexes in mixed upland habitats that were quite different from the savanna ones.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Funding

This paper is part of the Ph.D. project of G.B. supported by the Sapienza Università di Roma (three-year scholarship) in co-tutorship with the Eberhard Karls University of Tübingen. This research was further funded by the Deutscher Akademischer Austauschdienst (DAAD) (grant number 57552336) and by the Sapienza Università di Roma (grant number 0044296), both awarded to G.B. The stable isotope analyses were funded by the Biogeology working group (Department of Geosciences - University of Tübingen).

CRediT authorship contribution statement

Giuseppe Briatico: Conceptualization, Formal analysis, Investigation, Writing - original draft, Writing – review & editing, Visualization, Funding acquisition. Hervé Bocherens: Resources, Writing - review & editing, Supervision. Raymonde Bonnefille: Writing – review & editing. Denis Geraads: Writing – review & editing. Margherita Mussi: Resources, Writing – review & editing, Supervision, Project administration.

Acknowledgments

We thank the Authority for Research and Conservation of Cultural Heritage (ARCCH) and the National Museum of Ethiopia (Addis Ababa) for permission to sample the paleontological collection and access to the lab facilities, assistance during laboratory work, and the export permit of the faunal enamel samples. We are grateful to the curatorial staff for facilitating these steps.

Appendix A. Supplementary data

Supplementary data 1 (PDF document).

Supplementary data 2 (Excel document).

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Isotopic insights into the Early Acheulean (1.95 Ma-1.66 Ma) high-elevation paleoenvironments at Melka Kunture (Upper Awash, Ethiopia)

Status:

Version 1

Abstract

Figures

1. Introduction

1.1 Archaeological background

1.2 The faunal remains

1.3 The paleobotanical data

1.4 Carbon and oxygen stable isotopes analysis in tooth enamel

2. Materials And Methods

3. Results

3.1 The δ¹³C and δ¹⁸O values from Garba IVD

3.2 The δ¹³C and δ¹⁸O values from Gombore IB

4. Discussion

4.1 Dietary and paleoenvironmental reconstruction

4.2 The δ¹³C and δ¹⁸O comparison from tooth enamel in East Africa

5. Conclusions

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1

Isotopic insights into the Early Acheulean (1.95 Ma-1.66 Ma) high-elevation paleoenvironments at Melka Kunture (Upper Awash, Ethiopia)

Status:

Version 1

Abstract

Figures

1. Introduction

1.1 Archaeological background

1.2 The faunal remains

1.3 The paleobotanical data

1.4 Carbon and oxygen stable isotopes analysis in tooth enamel

2. Materials And Methods

3. Results

3.1 The δ13C and δ18O values from Garba IVD

3.2 The δ13C and δ18O values from Gombore IB

4. Discussion

4.1 Dietary and paleoenvironmental reconstruction

4.2 The δ13C and δ18O comparison from tooth enamel in East Africa

5. Conclusions

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1

3.1 The δ¹³C and δ¹⁸O values from Garba IVD

3.2 The δ¹³C and δ¹⁸O values from Gombore IB

4.2 The δ¹³C and δ¹⁸O comparison from tooth enamel in East Africa