The genus Macaca represents one of the most successful extant primate genera, exhibiting the second largest geographic distribution among primates, surpassed only by the genus Homo. Currently, macaques comprise multiple species and subspecies (Fooden, 1982; Rowe et al., 1996; Thierry, 2017; Roos et al., 2019). Extant macaque species are mostly found in Asia and occupy a broad range of habitats (Lehman and Fleagle, 2006). However, macaques are also represented in Africa by a single species, Macaca sylvanus, which is restricted to the isolated temperate forests of Algeria and Morocco (Fooden, 2007). In Asia, the genus is widely distributed from northern Japanese coniferous forests to Sumatran equatorial forests and shows high species diversity (e.g., Fooden, 1982; Fa, 1989; Goldstein and Richard, 1989; Riley, 2008; Tsuji, 2010; Roos et al., 2019). With the sole exception of a semi free-ranging colony of M. sylvanus in Gibraltar introduced by humans in historical times (Modolo et al., 2005), macaques are nowadays absent from Europe and Western Asia. Regardless, the fossil record indicates that macaques were widespread in Europe during the Plio-Pleistocene (e.g., Delson, 1980; Alba et al., 2021 and references therein).

According to the fossil record and more recent molecular evidence, the last common ancestor of macaques is dated to around 7.0–6.7 Ma in the Late Miocene of Africa (Szalay and Delson, 1979; Delson, 1980; Thomas and Petter, 1986; Benefit, 2008; Roos et al., 2019). As a result, the genus Macaca is the oldest cercopithecine found in Europe, where it probably dispersed from Africa by the latest Miocene (Köhler et al., 2000; Alba et al., 2014) in the context of faunal exchanges associated with the Messinian Salinity Crisis (Gibert et al., 2013). Around that time, the level of the Mediterranean Sea fluctuated and eventually desiccated, most likely facilitating the dispersal of the genus from North Africa (Alba et al., 2014; Roos et al., 2019). Nevertheless, macaque remains from the Late Miocene of Europe are scarce, with only two fossil sites reported, Almenara-Casablanca M in Spain (Köhler et al., 2000) and Moncucco Torinese in Italy (Alba et al., 2014). By the Early Pliocene, macaques were distributed along southern Europe, including eastern France and all the way to the modern Black Sea region (Delson, 1974; Alba et al., 2018). During the earliest Pleistocene, fossil representatives of Macaca reached as far as north as Tegelen in the Netherlands (Van den Hoek Ostende and de Vos, 2006). Toward the end of the Early Pleistocene, macaques maintained their broad distribution from northern to southern mainland Europe, where they persisted into the Middle Pleistocene (Elton and O'Regan, 2014; Konidaris et al., 2022). By the early Late Pleistocene (0.2–0.1 Ma), most of the European macaque fossil sites were found in Spain, but macaque remains are not solely restricted to the Iberian Peninsula as they have been recovered from a wider range of contemporary European sites (see Elton and O'Regan, 2014).

Plio-Pleistocene European macaques are represented by several taxa that belong to the lineage of M. sylvanus, the extant barbary macaque from North Africa (Szalay and Delson, 1979; Delson, 1980; Alba et al., 2008, 2011, 2018; Roos et al., 2019). Overall, three extinct subspecies of M. sylvanus are tentatively distinguished (Alba et al., 2008, 2018): Macaca sylvanus prisca, from the Pliocene of Europe, sometimes found associated with other fossil cercopithecids (i.e., Dolichopithecus and Mesopithecus; Eronen and Rook, 2004; Alba et al., 2014, 2018); Macaca sylvanus florentina, from the Late Pliocene to the Early Pleistocene of southern and central Europe (Alba et al., 2011; Rook et al., 2013; Marigó et al., 2014); and Macaca sylvanus pliocena, from the Middle Pleistocene of Europe plus Caucasus and Israel (Delson, 1980; Tchernov and Volokita, 1986; Maschenko and Baryshnikov, 2002). In turn, macaque remains from the Early to Middle Pleistocene of Sardinia are usually assigned to a distinct species, Macaca majori Azzaroli, 1946 (Gentili et al., 1998; Rook and O'Higgins, 2005; Zoboli et al., 2016).

Macaca majori was described on the basis of a large fossil sample found in Capo Figari fossil site (Golfo Aranci, northeastern Sardinia; Azzaroli, 1946). Additional fossil remains were recovered from other fossil sites, such as Is Oreris (Fluminimaggiore) in southwestern Sardinia and more recently from fissure fillings at Monte Tuttavista (Orosei) in southwestern and eastern Sardinia, respectively (Abbazzi et al., 2004; Palombo, 2006; Zoboli et al., 2016). Its overall smaller size compared to other contemporaneous fossil macaques from mainland Europe along with a series of craniodental differences support the presence of an endemic dwarfed distinct species in Sardinia (Rook and O'Higgins, 2005; Zoboli et al., 2016).

The chronostratigraphic range of M. majori remains uncertain (Sondaar, 1987; Sondaar and Van der Geer, 2005; Abbazzi et al., 2008; Palombo and Rozzi, 2014). Macaca majori was undoubtedly present in Sardinia during the Early to Middle Pleistocene (Van der Made, 1999), yet the time of arrival of the genus Macaca to Sardinia is unclear (see Palombo, 2006 and references therein). The absence of M. majori from the fossil record of Sardinia after the Middle Pleistocene suggests that the species became extinct by then, although the causes remain unknown (Abbazzi et al., 2004).

The dietary ecology of modern macaque species has been extensively studied (e.g., Maruhashi, 1980; Fooden, 1982; Fa, 1989; Krishnamani, 1994; Agetsuma, 1995; Hill, 1997; Ménard and Vallet, 1997; O'Brien and Kinnaird, 1997; Hanya et al., 2003; Pombo et al., 2004; O'Regan et al., 2008; Hanya et al., 2011; Albert et al., 2013; Sengupta et al., 2014; Richter et al., 2015; Tsuji et al., 2015). In general, extant macaques are usually regarded as opportunistic and highly eclectic feeders, exploiting a wide variety of food items available in their habitats (Fa, 1989; Thierry, 2011). They primarily depend on plant matter for food, even though they may supplement their diet with faunal resources like insects, invertebrates, eggs, fish, gastropods, and crustaceans (Fooden, 2000; O'Regan et al., 2008; Stewart et al., 2008; Pal et al., 2018). However, dietary information for fossil macaques is sparse (Ramírez-Pedraza et al., 2023) and there is a lack of information for fossil macaque species from Europe.

The presumed closest extant relative of fossil European macaques is Macaca sylvanus sylvanus from North Africa, which appears to prefer fruit and/or seeds such as acorns when available but also includes large amounts of leaves in its diet (Ménard and Vallet, 1997; Ménard, 2002). This seems to be a common dietary strategy in macaque species found in temperate habitats, such as Macaca fuscata from Japan and some Macaca mulatta populations found in high altitudes in China (Hanya et al., 2011; Sengupta and Radhakrishna, 2016; Cui et al., 2019, 2020). By contrast, species found in tropical habitats, such as Macaca nemestrina and Macaca nigra, apparently consume more fruits than do those in temperate and marginal zones (O'Brien and Kinnaird, 1997; Hanya et al., 2013; Ruppert et al., 2018). In addition, geographical and regional factors that affect the availability of vegetal resources may also influence the dietary choices of some macaque species (e.g., Agetsuma and Nakagawa, 1998; Hanya et al., 2003, 2004; Hanya, 2004). Since European Plio-Pleistocene macaques probably dwelled in temperate and marginal habitats, it may be assumed that they followed dietary strategies similar to those seen in extant temperate species (e.g., Elton and O'Regan, 2014). However, it must be noted that behaviors observed in modern species are not always equivalent to those of extinct taxa, especially when considering the anthropogenic effects on present-day ecosystems.

This work examines the dietary niches of fossil Plio-Pleistocene European macaques, focusing on M. majori from Sardinia. Previous research revealed that M. majori possesses some unique dental anatomical traits (overall more robust dentition with molars having a more ‘inflated’ morphology) compared with other species of the genus Macaca (Szalay and Delson, 1979; Zanaga, 1998). It has been previously assumed that these derived features might reflect specific dietary adaptations (e.g., Rook and O'Higgins, 2005), potentially toward an overall more durophagous dietary niche. Here, we evaluate this hypothesis by examining the molar morphology of M. majori along with its dental microwear texture. We assume that, if its molars possess some distinctive morphological features that could be suggestive of an overall more durophagous diet compared to other cercopithecids, this will also be reflected in its dental microwear textures. To that end, we first assess the molar morphology of M. majori (i.e., via enamel thickness and dental topography) using two fossil molars from two specimens from Capo Figari (Ty5199 and Ty5203; Fig. 1) and compare these with a broad sample of modern cercopithecids, which includes folivorous, fruit/seed, and mixed feeding species. We then assess the microwear textures of M. majori and compare them with a series of modern cercopithecids characterized by either folivorous, fruit/seed eating, or mixed feeding dietary habits. Furthermore, in the dental microwear comparative sample, we included two extant macaques found in temperate habitats (M. sylvanus and M. fuscata) and one in a more tropical habitat (M. nemestrina), along with other European mainland Macaca fossil specimens (here assigned to M. s. florentina). As previously mentioned, due to the opportunistic dietary nature of extant macaques, there are usually distinct differences in the dietary composition of macaques found in temperate habitats compared to macaques found in tropical habitats (Ménard, 2002; Hanya et al., 2011, 2013) that could be reflected in their microwear textures. Therefore, differences and/or similarities in the microwear textures between extant macaque species will allow us to better comprehend ecological factors that may have influenced the diet of the fossil European species (i.e., M. majori and M. s. florentina). In addition, as previous research suggests interpopulation differences in the dietary choices and feeding behavior of some temperate macaque species most likely associated with habitat differences (e.g., Maruhashi, 1980; Agetsuma and Nakagawa, 1998; Ménard and Qarro, 1999), it is possible that this also applied to European mainland fossil macaques and M. majori. To evaluate this possibility, we also explore microwear texture differences among three extant populations of a temperate macaque species in our microwear sample, M. fuscata, found in northern (Aomori), central (Nagano), and southern (Yakushima) Japan, with the assumption that potential microwear texture differences will enable us to better understand the dietary ecology of extant and fossil macaques found in temperate environments. Our results have important implications for understanding the diversity of the genus Macaca in Europe, its paleoecology during the Plio-Pleistocene and the dietary strategies of extant macaque species. If M. majori potentially occupies a dietary niche relatively distinct from the modern cercopithecids compared here and its European mainland fossil macaques, this may suggest that ecological differences among paleohabitats (e.g., European mainland and Sardinian insular) may have promoted different dietary strategies that favored certain feeding adaptations. This further implies that the opportunistic and generalist dietary nature of macaques may have been a key trait for their extensive geographic distribution and ecological success (e.g., Elton and O'Regan, 2014).