# A close-up at the paleoecology of the most western gelada relatives: Insights from dental microwear texture analysis

Margot Louail, Denis Geraads, Camille Daujeard, Rosalia Gallotti, David

Lefèvre, Abderrahim Mohib, Jean-Paul Raynal, Gildas Merceron

► To cite this version:

Margot Louail, Denis Geraads, Camille Daujeard, Rosalia Gallotti, David Lefèvre, et al.. A close-up at the paleoecology of the most western gelada relatives: Insights from dental microwear texture analysis. Journal of Human Evolution, 2026, 210, pp.103784. 10.1016/j.jhevol.2025.103784. hal-05395779

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A close-up at the paleoecology the most western gelada relatives: insights from dental microwear
texture analysis

Margot Louail<fnref n="1" />, <fnref n="2" />*, Denis Geraads<fnref n="3" />, Camille Daujeard<fnref n="4" />, Rosalia Gallotti<fnref n="5" />,<fnref n="6" />, David Lefèvre<fnref n="5" />, Abderrahim Mohib<fnref n="7" />,<fnref n="8" />, Jean-Paul Raynal<fnref n="6" />,<fnref n="7" />, Gildas Merceron<fnref n="2" />*

<footnote n="1">¹ Department of Human Evolutionary Biology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, United States</footnote>

<footnote n="2">² Laboratoire PALEVOPRIM, UMR 7262 CNRS & Université de Poitiers, TSA 51106, 86073 POITIERS Cedex 9, France</footnote>

<footnote n="3">³ CR2P, Muséum national d'Histoire naturelle (MNHN), UMR 7207 CNRS, Sorbonne Université, 8 rue Buffon, 75231 PARIS Cedex 05, France</footnote>

<footnote n="4">⁴ HNHP-UMR 7194, CNRS, MNHN, UPVD, Institut de Paléontologie Humaine, 1 rue René Panhard, 75013 Paris, France</footnote>

<footnote n="5">⁵ LabEx ARCHIMEDE, et UMR 5140 Archéologie des sociétés méditerranéennes, Université de Montpellier Paul Valéry – CNRS, Campus Saint Charles, 34199 Montpellier, France.</footnote>

<footnote n="6">⁶ Université Bordeaux, CNRS, UMR 5199 PACEA-PPP, Bâtiment B18 Allée Geoffroy Saint-Hilaire CS 50023, 33615 Pessac Cedex, France.</footnote>

<footnote n="7">⁷ Institut National des Sciences de l'Archéologie et du Patrimoine (INSAP), Rabat, Morocco.</footnote>

<footnote n="8">⁸ Direction provinciale de la Culture, Avenue Mohammed V, quartier administratif, Kénitra, Morocco.</footnote>

<footnote>*Corresponding authors: margotlouail@g.harvard.edu and gildas.merceron@univ-poitiers.fr</footnote>
**Abstract**

Exploring the paleoecology of extinct species of the genus *Theropithecus*, which was widespread and diversified in Africa during the Pliocene and the Pleistocene, is crucial to have a full picture of the evolutionary history of this taxon. It also gives insights into the fundamental ecological range of the genus, now restricted to the Ethiopian highlands in a reduced set of habitats. This study aims to investigate the diet of *Theropithecus atlanticus* (n = 8) from the Plio-Pleistocene site of Ahl al Oughlam (Morocco) through dental microwear texture analysis. We used a recently developed software, 'trident', that quantifies the heterogeneity of texture parameters through subsampled wear surfaces to improve dietary discriminations. We considered a comparative dataset of extant primates (n = 104) with different diets, including the leaf-eater *Colobus guereza*, the grass-eater *Theropithecus gelada*, and the generalists *Papio hamadryas* and *Chlorocebus aethiops*. In addition, we compared with specimens of theropiths (n = 80) from the eastern African Shungura Formation (Lower Omo Valley, Ethiopia) that are nearly contemporaneous to *T. atlanticus*. Our results indicate that *T. atlanticus* was mostly feeding on grasses, as its extant relative. Some similarities with opportunistic species suggest it might have consumed a substantial amount of challenging foods. This dental microwear texture is in line with open, arid and harsh environments, and the presence and abundance of C3 grasses at Ahl al Oughlam detected by enamel stable isotopes analysis on various mammals including theropiths. This contrasts with the environment described on nearly contemporaneous specimens from the Lower Omo Valley where grasses were abundant but composed of C4 ones.

**Keywords**

North Africa; Paleoecology; Dental abrasion; Multivariate analysis; trident
# 1. Introduction

The gelada baboon, *Theropithecus gelada*, is an iconic species of Ethiopia (Figure 1A). This large monkey has a special place for biological conservation in Africa, as the gelada occupies a restricted area in mountains and its ecology constrains it to exploit mostly, if not only, open alpine meadows where it feeds on herbaceous monocots and dicots (Figure 1B; Iwamoto, 1993; Fashing et al., 2014; Abu et al., 2018; Jarvey et al., 2018). Ahmed, Chala et al. (2023) highlight that the species occupies sub-optimal habitats where human disturbances are lower. Gelada can be defined as a refugee species with a quite narrow realized niche (Kerley et al., 2012; Kuemmerle et al., 2012). Ahmed, Chala et al. (2023) question the species' future in the context of climate changes and the expansion of anthropic activities in the High Plateaus and propose scenarios until the end of the century. Their conclusions are quite pessimistic as the optimal habitat of this monkey cannot altitudinally extend anymore. However, the gelada's historical and paleontological record could complete our knowledge of its fundamental niche, and thus its adaptability to face climate changes and human encroachment upon its habitat.

The genus *Theropithecus* was diversified and widespread in the Pliocene and the Pleistocene. It occurred in multiple sites from South Africa to Ethiopia along the East African Rift with at least two species (*Theropithecus brumpti*, and the lineage including *Theropithecus darti* and *Theropithecus oswaldi*), as well as in the most northwestern corner of Africa (with *T. atlanticus*) and even in the Iberic peninsula with specimens attributed to *T. oswaldi* (Gibert et al., 1995; Hughes et al., 2008; Jablonski and Frost, 2010; Getahun et al., 2023; Figure 1A). This demonstrates the importance to consider past biodiversity to have a full view of the fundamental ecological niche of extant taxa to propose adapted conservation policies. The large repartition of *Theropithecus* is the result of the back-and-forth latitudinal dispersal of mammalian groups from the Late Miocene to the Early Pleistocene due to several favorable Green Sahara Periods (Larrasoaña et al., 2003, 2013; Schuster et al., 2009; Zhang et al., 2014; Grant et al., 2017; Larrasoaña, 2021). This came out with rich and diversified mammalian communities in northern Africa with affinities with sub-Saharan faunas (Thomas et al., 1982; Boaz et al., 1987; Geraads et al., 1998; Geraads, 2010, 2022; Bibi, 2011).

The site of Ahl al Oughlam, located in an abandoned sandstone quarry near Casablanca (Morocco; Figure 1A), is the richest site of the Late Cenozoic in Northern Africa, with more than 100 species of vertebrates identified upon more than 4000 fossil remains found in karstic and fissure fillings. No absolute dating is possible, but biochronology suggests an age of between 2.8 and 2.4 Ma (Geraads et al., 1998; Geraads, 2010; Raynal et al., 1990; Geraads, 2006; Geraads et al., 2022). The faunal composition shows affinities with the faunas from contemporaneous eastern African sites, as numerous species and most genera have also been described in eastern and southern African sites (Geraads, 2010; Geraads et al., 2022). Noticeably, *Theropithecus* is the only primate species recovered from Ahl al Oughlam, which contrasts with other African sites from the Pliocene and the Pleistocene where several primate species (cercopithecids, hominids) are usually found (e.g. Jablonski and Frost, 2010). The taxonomy of *Theropithecus* from Ahl al Oughlam is debated. Some authors consider the specimens from Ahl al Oughlam as early representatives of *Theropithecus oswaldi oswaldi* (Frost and Delson, 2002), while others consider them as belonging to a distinct species, *Theropithecus atlanticus* (Geraads et al., 2022; Alemseged and Geraads, 1998; Geraads and Alemseged, 2022). In this paper, we make no claim to contribute to this debate, and we use *T. atlanticus* because it is the most commonly employed in the literature to refer to theropiths from Ahl al Oughlam.

Although recent studies have challenged the vision of modern gelada being strict graminivores (Fashing et al., 2014; Jarvey et al., 2018; Shapiro et al., 2016), Hughes et al. (2008) argued that extinct species were likely more ecologically flexible than *T. gelada*. The dietary niches of extinct theropiths from sub-Saharan Africa have been the focus of several works (Cerling et al., 2013; Levin et al., 2015;
Martin et al., 2018; Merceron et al., 2021; Souron, 2018; Wynn et al., 2016). Besides that, they have been barely studied in northern Africa or Eurasia (Fannin et al., 2021; Martínez et al., 2020). While enamel carbon stable isotopes are highly informative to target the feeding resources of mammals in intertropical latitudes as the repartition of C₃ and C₄ plants informs about tree cover density (but see Souron, 2018 who pointed out the non-negligible presence of C₃ forbs and graminoids in lowland Africa during the Plio-Pleistocene), this proxy is nearly inefficient when considering higher latitudes in Europe or even northern Africa (but see Drucker et al., 2008 on the canopy effect). This is due to the absence of a large expansion of C₄ plants in those regions, meaning both dicots and monocots have for most of them a C₃ metabolic pathway. Dental microwear could overpass that limitation in this specific case. It is highly dependent on the mechanical properties and biosilica content of masticated food items (Daegling et al., 2016; Lucas et al., 2014, 2013; Merceron et al., 2016), and records literally new scars after every cycle of mastication. It came out that dental microwear reflect the physical properties and tissue contents of the last few days to about two weeks prior to death (Teaford et al., 2021, 2017; Teaford and Oyen, 1989; Winkler et al., 2020). This allows to track seasonal variations in diet (Teaford and Robinson, 1989; Merceron et al., 2010; Berlioz et al., 2017; Percher et al., 2017). It can thus provide major insights into past diets and can complement data from other paleodietary proxies such as biogeochemistry that gives information on the chemical properties of the diet.

Dental Microwear Texture Analysis (DMTA) has proven its efficiency in detecting differences between species with contrasted diets (e.g. Ungar et al., 2003, 2007; Scott et al., 2006, 2012; Schulz et al., 2010, 2013; Scott, 2012; Hullot et al., 2019; Merceron et al., 2021; Louail et al., 2025), as well as small variations within species or populations, which could reflect seasonal or sex-related dietary variations (Berlioz et al., 2017; Louail et al., 2025; Merceron et al., 2014, 2010; Percher et al., 2017; Shapiro et al., 2016). To date, only three studies investigated dental microwear in mammals from northern African Plio-Pleistocene sites: Ramírez-Pedraza et al. (2023b) on herbivores from Ahl al Oughlam and Ramírez-Pedraza et al. (2023a, 2024) on *Macaca* and ungulates from Guefaït-4.2, respectively. Among them, only one has applied DMTA on non-occlusal facets of *Macaca* from the later site (Ramírez-Pedraza et al., 2023a). None has yet focused on dental microwear patterns of *T. atlanticus*.

To fill this gap, the main objective of this study is to contribute to understanding the diet of *T. atlanticus* from the Moroccan site of Ahl al Oughlam using DMTA. Extant primate species can sometimes show notable overlaps in some standard Scale-Sensitive Fractal Analysis (SSFA) parameters (Scott et al., 2012; Martin et al., 2018; Merceron et al., 2021; see also Figure 1 in Thiery et al., 2024 and SOM1). To go beyond this limitation, we used the recently developed trident software (Thiery et al., 2024), which quantifies the heterogeneity of texture parameters over single surfaces. This software implements the surface subsampling routine published by Francisco, Brunetière et al. (2018b; see also Francisco et al., 2018a). The subsampling routine has recently shown its efficiency in improving dietary discriminations (Francisco et al., 2018b, 2018a; Louail et al., 2021; Merceron et al., 2021), and the trident software now proposes an open-access and user-friendly graphical interface for more accessibility to the community and repeatability of measurements (Thiery et al., 2024). We used trident to update the reference model on extant primate species built by Merceron et al. (2021). Then, using this reference model, we aimed at investigating the past feeding ecology of *T. atlanticus* from Ahl al Oughlam. For comparison purposes with nearly contemporaneous theropods, we included into this analysis specimens from Member C, Member D and Member E of the eastern African Shungura Formation (Lower Omo Valley, Ethiopia), ranging from ca. 2.9 Ma to 2.3 Ma.

## 2. Materials and Methods
**2.1. Extant and fossil primate samples**

To build the reference primate model, we used a total of 104 wild specimens from four modern primate species with different dietary habits: the leaf-eater *Colobus guereza* (n = 19), the grass-eater *Theropithecus gelada* (n = 21), and the two generalists *Papio hamadryas* (n = 27) and *Chlorocebus aethiops* (n = 37). This sample was composed of the same specimens and scanned wear surfaces as in Merceron et al. (2021). Specimens are stored at the *Muséum national d'Histoire naturelle, Paris* (France), at the Ethiopian Heritage Authority (Addis Ababa, Ethiopia) and at the *Musée des Confluences* (Lyon, France). A detailed description of the samples including provenances and dates of sampling is shown in Merceron et al. (2021).

The fossil specimens of *Theropithecus atlanticus* were collected from the site of Ahl al Oughlam. Specimens will be stored at the Institut National des Sciences de l'Archéologie et du Patrimoine (Rabat, Morocco). After careful examination of all dental material belonging to *Theropithecus atlanticus* from Ahl al Oughlam, we analyzed only eight worn upper or lower first, second or third molars (one tooth per specimen; Figure 1; SOM1: Table S1). We discarded non worn or barely worn molars. Also, we made the choice to target specimens with both phase I and phase II molar facets well preserved. Besides, some teeth showed weathering alteration which impacts enamel surface at the micrometric scale; those have been then discarded. To compare the dietary ecology of Ahl al Oughlam theropiths with theropiths from about the same period, we included specimens from Member C (n = 65), Member D (n = 9) and Member E (n = 6) of the Shungura Formation (Lower Omo Valley, Ethiopia), representing a period from ca. 2.9 Ma to 2.3 Ma. All specimens from Shungura have been attributed to either *Theropithecus brumpti* or *Theropithecus* sp. (Eck, 1987) (n = 26 and n = 54, respectively; see SOM2), and have been analyzed in Martin et al. (2018) and Merceron et al. (2021).

**2.2. Dental Microwear Texture Analysis**

Extant samples are mostly composed of upper and lower second molars (M2). Fossil samples are composed of upper and lower first (M1), second and third (M3) molars. We gave priority to M2 but we focused on M1 or M3 when necessary (SOM2). All specimens were cleaned, molded and scanned following the standard procedures described in Martin et al. (2018). For each specimen, we included one shearing facet (phase I) and one crushing facet (phase II) of the same tooth (Figure 1). Each facet was carefully cut on the silicon molds and scanned as horizontal as possible using “TRIDENT”, the Leica DCM8 white light confocal profilometer housed at the PALEVOPRIM lab (CNRS and University of Poitiers; magnification set at 100×, numerical aperture: 0.90; working distance: 0.9 mm; Leica Microsystems). Scanned surfaces were pre-treated under LeicaMap v. 8.0 (Leica Microsystems, Mountain technology) by removing abnormal peaks, filling non-measured points (representing less than 3 % of all measured points) and leveling the surfaces (see Merceron et al., 2016 for more details). A 200 × 200 µm (1551 × 1551 pixels) leveled area was automatically generated from each surface and used for Dental Microwear Texture Analysis. Photosimulations and false-color elevation maps are provided as supplementary materials (SOM3).

We employed the recently published trident software (Thiery et al., 2024). This method quantifies the heterogeneity of surface texture through a surface subsampling routine, which considers parameters (SOM1: Table S2) that are more or less modified from the international standard ISO 25178 (Francisco et al., 2018b, 2018a; Thiery et al., 2024). We computed a large set of variables including one global value over the whole surface (without subsampling) for each of the 24 microwear parameter, as well as nine statistics (mean, median, standard deviation, values at first and third quartiles, mean of
values below and above first and third quartiles, skewness, kurtosis) for each parameter calculated through subsampled surfaces. From this dataset, trident identifies the discriminative variables between groups. See Thiery et al. (2024) and SOM4 for more details on the procedure. Following a similar approach as in Merceron et al. (Merceron et al., 2021), we selected the variable, for each parameter, that targets the highest number of discriminated groups following Fisher's LSD tests and lowest average LSD p-value. The final dataset is composed of 45 discriminative variables (22 on crushing facets and 23 on shearing facets; SOM1: Table S3).

<figure><img src="image_2.png" /><figcaption>**Figure 1.** (A) Main localities or region with extinct *Theropithecus* in Africa and Europe, (B) geographical distribution of the modern *Theropithecus gelada* in Ethiopia (modified after (Ahmed et al., 2023)); and (C) Occlusal (top) and lateral (bottom) views of the specimen AaO 228 (*Theropithecus atlanticus*). Dental microwear texture analysis has been run on (D) the shearing facet #6 and on (E) the crushing facet #9. Here, enamel surfaces are shown with elevation maps and photosimulations. One could see rougher surface on the crushing surface than on the shearing one.</figcaption></figure>

## 2.3. Statistical analyses

All graphical representations of data and statistical analyses were conducted in the R statistical environment (R Core Team, 2022; v.4.1.3; SOM4). The design of the graphics has been further refined using Inkscape. A Principal Component Analysis (PCA) was performed using the combined set of discriminative microwear variables gathered from trident on both crushing and shearing molar facets on extant primates (SOM1: Tables S3). Fossil theropiths from Ahl al Oughlam and from Shungura were
inserted into this reference extant monkey model as supplementary individuals. Three standard
parameters of the Scale-Sensitive Fractal Analysis (SSFA; Scott et al., 2006) have been calculated and
inserted into the PCA as supplementary variables (see supplementary information in SOM1): the
complexity (Asfc), the anisotropy (epLsar) and the heterogeneity of complexity calculated through 9×9
cells (HAsfc81). The PCA was conducted using the R packages “FactoMineR” (Lê et al., 2008; v.2.11),
“ggplot2” (Wickham, 2016; v.3.5.2), and “factoextra” (Kassambara and Mundt, 2020; v.1.0.7). The PC
coordinates were Box-Cox transformed to meet the assumption of normal distributions. Due to
heterogeneity of variances, we performed Welch's ANOVAs on PC coordinates to detect significant
differences between extant and extinct primates (SOM1: Table S4). Pairwise comparisons were tested
using Games-Howell posthoc tests using the R package “rstatix” (Kassambara, 2023; v.0.7.2) (SOM1:
Table S5).

**3. Results**

**3.1. The extant monkey model**

We selected PC1 and PC3 to build the updated extant monkey model (Figures 2 and 3; see also
SOM1). We considered PC3, rather than PC2 and PC4 (SOM1: Figures S1 and S2), because it provides
the greatest distinction between all species, particularly between *T. gelada* and *P. hamadryas*. PC1
explains 32.9 % of the total variance and is four times more informative than PC3, which explains 8.0
% of the variance (Figure 2A). The variables that most contribute to PC1 are central and dispersal
statistics of parameters related to the height distribution of surface roughness on both crushing and
shearing facets (Figure 2B, 2C). Topological parameters on both crushing and shearing facets, and
spatial parameters (mostly on crushing facets), contribute as well to PC1 (Figure 2B, 2C). The variables
that most contribute to PC3 are dispersal statistics of height and topological parameters on both types of
facets, as well as the first quartile of complexity (Asfc2) on shearing facets (Figure 2B, 2D). Spatial
parameters (mostly on crushing facets) contribute as well to PC3 but to a lower extent (Figure 2B, 2D).
Along PC1, *Colobus guereza* shows the lowest values and *Chlorocebus aethiops* the highest (Figure 3).
They significantly differ from each other (SOM1: Table S5). Median values of arithmetical mean height
(Sa) and root mean square height (Sq, or standard deviation of heights) on crushing facets contribute to
pull *Chlorocebus aethiops* toward high values along PC1. Conversely, 25 % minimal values of mean
height (Sm) and mean value of the deepest pits (Sv) on crushing facets contribute to pull *Colobus
gbereza* toward low values along PC1 (Figure 3). Both papionin species, *Theropithecus gelada* and
*Papio hamadryas*, show intermediate and overlapping values along PC1, and significantly differ from
*Colobus guereza* (SOM1: Table S5). Along PC3, *Theropithecus gelada* shows the highest values and
*Chlorocebus aethiops* the lowest (Figure 3). The two other species, *Colobus guereza* and *Papio
hamadryas*, show intermediate values but overlap with *Chlorocebus aethiops* (Figure 3). Lower values
of *Chlorocebus aethiops* along PC3 are notably explained by a greater amount of very rough shearing
facets, as reflected by their values of the last quartile of complexity (Asfc2) and the standard deviation
of relative area (Sdar). This is also reflected by Asfc (the standard SSFA parameter on global surfaces)
inserted as supplementary variables in the PCA (Figures 2 and 3). Conversely, the 25 % minimal values
of median relative area of the cells with the highest heights (Smc1) on crushing facets contribute to pull
*Theropithecus gelada* toward high values along PC3 (Figures 2 and 3).

The three supplementary variables issued from the SSFA on each of the two facets of molars
that compose the comparative dataset of extant species are plotted in the circle of correlations (see also
SOM1: Figure S3 and Tables S6 to S17). The inter-individual dispersion maximized by the PCA built
up with a set of the most discriminant texture parameters issued from trident, could have also been
reflected by the difference in texture complexity (Asfc) on both facets. However, this is not reflected by
the heterogeneities of complexity (HAsfc81) and the texture anisotropies (epLsar; Figure 2).
<figure><img src="image_3.png" /><figcaption>A)</figcaption></figure>

Principal components

<figure><img src="image_4.png" /><figcaption>B)</figcaption></figure>

PC1 (32.9 %)

Parameters

Family:

Height

Asfc2

Topological

Spatial

Supplementary SSFA

Facets:

Crushing

Shearing

<figure><img src="image_5.png" /><figcaption>D) Contribution of variables to PC3</figcaption></figure>

<figure><img src="image_6.png" /></figure>
**Figure 2.** Principal Component Analysis based on the 45 discriminative variables on shearing and crushing molar facets. (A) Eigenvalues or percentages of explained variance of the principal components. (B) Correlation circle along PC1 and PC3 including active variables (height: black lines, Asfc2: purple lines, topological: grey lines, and spatial: red lines) and supplementary SSFA parameters (Asfc, epLsar and HAsfc 81, pink lines). Dotted and solid lines indicate discriminative variables on shearing facets and on crushing facets, respectively. (C) Contributions (positive: "+", negative: "-") of active variables (height: black, Asfc2: purple, topological: grey, and spatial: red) on both crushing (solid contours) and shearing facets (dotted contours) to PC1. (D) Contributions (positive: "+", negative: "-") of active variables (height: black, Asfc2: purple, topological: grey, and spatial: red) on both crushing (solid contours) and shearing facets (dotted contours) to PC3.

**3.2. Insertion of fossil theropiths into the extant monkey model**

<figure><img src="image_7.png" /></figure>

**Figure 3.** Distributions of extant primates and fossil theropiths along principal components 1 and 3. Mean and mean confidence intervals at 95 % are represented (thick contours and letters), as well as individual data points for samples less than n = 10, i.e., fossil theropiths from Shungura Member D and Member E (normal letters) and from Ahl al Oughlam (stars without contours). Extant primates (solid lines) and fossil theropiths (dotted lines) are labelled with Member in capitalized letters.

When inserted into the extant monkey model, *T. atlanticus* plots close to its extant relatives. Its average value along PC1 appears more similar to extant *Chlorocebus aethiops* and is lower than extant geladas along PC3 (Figure 3). Among the eight specimens, one specimen showing a substantially high value along PC1 and a low value along PC3, and two other specimens showing substantially low values along PC3 explain this pattern (Figure 3). When removing this extreme specimen from the analysis, which shows a great relief amplitude (SOM 3), the average value of *T. atlanticus* is strongly similar to extant
geladas (SOM1: Figure S4). The sample of *T. atlanticus* strongly differs from the folivorous *Colobus guereza* along PC1 but not from other extant species, and no significant difference is detected along PC3 (SOM1: Table S5). Overall, specimens of *T. atlanticus* appear similar to theropiths from Shungura, either from Member C, Member D or Member E, which all plot next to their extant relatives. No significant difference is detected along both PCs between samples of fossil theropiths (SOM1: Table S5). It is worth noting that while theropiths from Shungura are strongly overlapping along PC3, samples from Member C and Member D overlap much less along PC1, and the sample of *T. atlanticus* appears on average more similar to theropiths from Member D along this PC. At comparable sample sizes, the sample of *T. atlanticus* seems more variable than theropiths from Member D and Member E (Figure 3).

**4. Discussion**

As pointed out above, species may sometimes overlap in some standard SSFA parameters (see SOM1 and Thiery et al., 2024). To overpass this limitation, we used the trident software (Thiery et al., 2024) that explores the variation of texture parameters through subsampling on both shearing and crushing molar facets, and allows generating a single PCA with the most discriminative variables on both facets. We observe significant contributions of central and dispersal statistics of height parameters, as well as of the mean value of smallest heights, along PC1. The PC3 discriminates *T. gelada* from other monkeys thanks to the topological variables included in trident (Thiery et al., 2024). Overall, we can define four ecospaces. Leaf-eating monkeys show low values along PC1, whereas opportunistic species including challenging food items display high values. The third component distinguishes the two species of papionins, with extant geladas displaying high values that identify their specialization on the herbaceous layer. It is worth noting that these ecospaces depend on the variables, the species and specimens selected in the PCA.

Inserted into this extant monkey model, *T. atlanticus* plots on average close to their extant relatives. However, contrary to the gelada baboon, *T. atlanticus* displays no significant differences with *Ch. aethiops* and *P. hamadryas*. The mean value along PC3 is intermediate between extant species of *Theropithecus* and *Papio* (Figure 3). The high average position of *T. atlanticus* along PC1 is undoubtedly strongly influenced by the extreme value displayed by one outlier specimen. Their dental microwear textures suggest that while *T. atlanticus* probably included a substantial amount of herbs in its diet, but it might have been less specialized on the herbaceous layer than modern geladas, relying more on challenging foods. This is also supported by the SSFA parameters, particularly as reflected by complexity (Asfc) of the shearing facets (SOM1: Figure S3). Such a dental microwear texture was previously observed by Shapiro et al. (Shapiro et al., 2016) on specimens of gelada baboon wild caught during dry seasons, when geladas tend to shift to underground storage organs (USOs) while the resources of tender grasses drop. Some specimens of *T. atlanticus* even show highly heterogeneous surfaces (SOM1: Figure S3) resembling those observed in *Chlorocebus aethiops*, which has opportunistic feeding habits that are important for coping with harsh environmental conditions (Alelign et al., 2023).

Extinct theropiths from Shungura plot next to extant geladas, suggesting similar reliance on herbaceous plants. Compared with specimens from Member C and Member E, theropiths from Member D and from Ahl al Oughlam tend to show higher values along PC1 than the extant geladas. This might indicate that theropiths from Ahl al Oughlam might have had feeding habits more similar to those from Shungura Member D. However, the lack of significant differences, their small sample size and the presence of one specimen with extreme values prevent us from making definitive judgements about the similarities in dietary composition of these two contemporaneous samples of extinct *Theropithecus* (SOM1: Table S5). While the observed differences between theropiths from Shungura and *T. atlanticus*
suggest that the mechanical properties of their diets differed to some extent – with *T. atlanticus* likely relying more heavily on challenging foods, similar to what has been suggested for extinct theropods in southeastern Spain from Early Pleistocene (Martínez et al., 2020) – the same limitations apply. These differences could also reflect different plant growth conditions between the two sites, with wetter environmental conditions at Shungura than at Ahl al Oughlam between 2.8 and 2.4 Ma (Barr, 2015; Levin et al., 2011).

To sum up, our results suggest that the feeding habits of *T. atlanticus* were overall similar to their extant relatives. While C₃ herbaceous monocots probably made a large part of their diet (hence our present results and their low δ¹³C values; Fannin et al., 2021), their feeding habits might have been more diversified than the one of extant geladas and included challenging food items. Recent studies investigated stable carbon and oxygen isotope compositions, as well as dental wear, in herbivores and primates from Plio-Pleistocene sites in Morocco (Fannin et al., 2021; Ramírez-Pedraza et al., 2024, 2023b, 2023a). These works highlighted the predominance of C₃ plants over C₄ plants in northern Africa in relatively dry and open environments. The absence of C₄ plants (or small proportion, see Ramírez-Pedraza et al., 2024) does not exclude the presence and abundance of herbaceous monocots. Fannin et al. (2021) on stable carbon and strontium isotopes have previously pointed out that C₃ plants predominate over C₄ plants in northern African ecosystems. A diet comprised of C₃ herbaceous monocots along with some challenging items would be congruent with the open, dry and harsh environmental conditions suggested at Ahl al Oughlam. At Ahl al Oughlam, bovid taxa with affinities for open environments such as Alcelaphini and Antilopini predominate over Tragelaphini. The extant representatives of the latter tribe are commonly associated with more wooded or bushy landscapes, while the modern species of the two former tribes occupy drier and open habitats (Geraads et al., 2022). Based on a recent study (Ramírez-Pedraza et al., 2023b), it appears that the vast majority of these bovids were C₃-plant eaters, which is not unexpected as the site is located in the Palearctic biomes where C₄ plant did not expand so much (Cerling et al., 1997). Furthermore, using the Kohn classification based on δ¹³C, the authors concluded that the site of Ahl al Oughlam was part of arid environments with mean annual precipitation (MAP) lower than 500 mm.y⁻¹, more than two times less than the MAP known in the High Ethiopian Plateau today where the last gelada baboon live (Ahmed et al., 2023). As resources of herbaceous monocots decrease, the dietary composition of *Theropithecus atlanticus* likely relied more on fallback foods such as underground storage organs compared with its extant relatives for which the higher precipitations maintain resources from the herbaceous layer available. Among bovids, the presence of mixed feeders and browsers (Ramírez-Pedraza et al., 2023b) also supports a seasonal drop in herbaceous monocots in seasonal and arid habitats. Grazing species would have either migrated to favorable habitats where the resources of preferred food are still available or widened their diet including dicot vegetation whose rooting systems go deeper and which are therefore more resistant to seasonal dryness (Hipondoka et al., 2003; Kulmatiski and Beard, 2013). However, the presence of reducines which are not considered in Ramirez-Pedraza et al. (2023b; but see Geraads et al., 1998; Geraads, 2022) advocates for the presence of permanent water or at least spots. Such wet habitats, even restricted, may have favored the maintenance of many species of mammals in the area to pass through the driest seasons as resources drop.

When considering the wide distribution of the genus during Plio-Pleistocene, the feeding habits of *T. atlanticus* in Ahl al Oughlam were more diverse than the ones of the extant gelada restricted to Ethiopia, and considering the associated fauna including notably arid-habit dwellers as well as the ecological and climatic proxies extracted from the dental tissues of these mammals of Ahl al Oughlam, we could conclude that the genus *Theropithecus* was and might be more resilient than the current status
let hypothesize. Multiple factors, including competition with other taxa and environmental changes, some of which likely linked to human disturbances might explain the shrinkage of the genus in Africa.

## Conclusion

Using a comparative dataset of extant primates, we analyzed dental microwear textures using trident, a new free and open access software to extract texture parameters and their heterogeneity over surface from crushing and shearing molar facets. We then extracted the most discriminant variables for each texture parameter, which allowed us to conduct a Principal Component Analysis to define an ecospace in which leaf eaters, grass eaters and opportunistic monkeys significantly differ from each other. Fossil specimens of *T. atlanticus* from Ahl al Oughlam as well as the specimens of *Theropithecus* from the members C to E of the Shungura Formation are inserted as supplementary data. Our results suggest that *T. atlanticus* mostly fed on herbaceous plants in a similar way to its extant relatives. Some similarities with the opportunistic *Chlorocebus aethiops* suggest it may have relied more on harder resources than extant geladas or contemporaneous theropiths from eastern Africa. While the sample size studied here is low, this microwear pattern is convergent with the hypothesis of relatively more open, drier, and probably harsher environments at Ahl al Oughlam than in eastern Africa at the same period. Our results with former studies would rather advocate for an ecological plasticity of the genus *Theropithecus* including the extant gelada that would allow it to face the effects of ongoing climate changes if human disturbance does not superimpose its impacts on it.

## Conflict of interest

The authors declare no competing interest.

## Acknowledgments

This study was founded by the Palevoprim Lab (CNRS and Université de Poitiers, France), and the ANR project DIET-Scratches (ANR-17-CE27-0002-02, PIs: G. Merceron and S. Ferchaud; French Agency for Research). ML was funded through the ALIHOM project (project n°210389, *Nouvelle-Aquitaine region*, France, PI: G. Merceron) and the *Ministère de l'Enseignement supérieur, de la Recherche et de l'Innovation* (France). Excavations at Ahl al Oughlam were conducted by D. Geraads from 1989 to 2004 in the framework of the “Préhistoire de Casablanca” Moroccan-French program led at that time by J.-P. Raynal and F.-Z. Sbihi-Alaoui, and supported by the *Institut National des Sciences de l'Archéologie et du Patrimoine* (INSAP) of the *Ministère de la Jeunesse, de la Culture et de la Communication/Département de la Culture* of the Kingdom of Morocco, and the *Ministère de l'Europe et des Affaires Étrangères* (France), the LabEx ARCHIMEDE - ANR-11-LABX-0032-01, the Aquitaine Region through the "Origines" project, the Collège de France, the Muséum national d'Histoire naturelle, Paris, the HNHP lab, the CNRS, the PACEA lab (France), and the Department of Human Evolution of the Max Planck Institute for Evolutionary Anthropology in Leipzig (Germany). Thanks to Fethi Amani and the Casablanca workers who participated in the excavations, especially Abdeslam Nader, Abdelali Khadouma and Hassan Caid Rha. The authors thank S. Riffaut from the Palevoprim Lab (CNRS and Université de Poitiers, France) for the figure preparation.

## Data availability
Dental Microwear Textures of *Theropithecus* from Ahl Al Oughlam and extant species are available in the repository InDores. All raw scans of surfaces (.plu files), the template used to pre-treat raw data (.mnt files), as well as the surfaces (.sur files) used with trident are provided here:

Extant species of Ethiopian Cercopithecids

https://doi.org/10.48579/PRO/XYASLG

Fossil specimens of *Theropithecus* from Ahl Al Oughlam

https://doi.org/10.48579/PRO/T3EM3Y

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