These analyses had, however, a significant gap, because late Middle Miocene taxa were not included due to the scarcity of fossil specimens from this time span. This situation, however, drastically changed during the last decade thanks to continued and extensive fieldwork in the late Middle Miocene local stratigraphic series of Abocador de Can Mata in els Hostalets de Pierola (Vallès-Penedès Basin) [4] , [27] , [28] . The material recovered there has shown an unprecedented diversity of Middle Miocene dryopithecines in Western Europe [3] , [4] , with two new genera and species (Pierolapithecus catalaunicus [29] and Anoiapithecus brevirostris [30] ) being described, and new material of Dryopithecus fontani [31] being recovered. Similarly, excavations at several Late Miocene localities of the same basin have led to the recovery of new dental remains of Hispanopithecus laietanus, which further confirm the distinction of this species from Hispanopithecus crusafonti, recorded at slightly older localities [4] . Additional paleodietary data are therefore required for these taxa in order to better understand the hominoid radiation in Western Eurasia from a dietary viewpoint.

Previous dental microwear analyses were based on a wide array of extinct hominoids from the Miocene of Western Eurasia [10] – [12] : Griphopithecus alpani [16] , [17] from the early Middle Miocene (MN6, ca. 14.9–13.7 Ma) [3] of Turkey; Hispanopithecus (Rudapithecus) hungaricus [18] , [19] from the Late Miocene (MN9, ca. 10.0–9.8 Ma) [3] of Hungary; Ouranopithecus macedoniensis [20] – [22] from the Late Miocene (MN10, ca. 9.7–9.0 Ma) [3] of Greece; Oreopithecus bambolii [23] – [25] from the Late Miocene (MN12, ca. 8.3–6.7 Ma) [26] of Italy; and Hispanopithecus crusafonti (MN9, ca. 10.4–10.0 Ma) and Hispanopithecus laietanus (MN9, ca. 11.1–9.5 Ma) [4] from Spain [3] . Results based on these taxa [10] – [12] suggested that, from the hard-object feeding plesiomorphic condition displayed by G. alpani [12] , a progressive dietary diversification and specialization would have taken place through time—with Hispanopithecus spp. being inferred as a frugivore [10] , [11] , Ou. macedoniensis as a hard-object specialist [10] , and O. bambolii as an extreme folivore [10] .

After an initial radiation in Africa during the Early to Middle Miocene [1] , hominoids dispersed into Eurasia, where they diversified into multiple great ape genera from ca. 14 Ma onwards [2] – [6] . Available data suggest that vicariance and parallel evolution played a significant role in the Eurasian hominoid radiation, with dryopithecines diversifying in Europe, pongines in Asia, and maybe hominines in Africa [3] , [4] . Dietary adaptations have long been regarded as very significant for understanding the dispersal of hominoids from Africa into Eurasia and their subsequent radiation [4] , [6] – [8] . Paleodietary inference is thus paramount for understanding how fossil great apes adapted to changing environmental conditions through time. Unlike in hominins, however, comparatively little dietary research has focused on fossil great apes from Eurasia [7] – [15] . Previous results suggest that a considerable dietary diversity was present in the Late Miocene, and that such diversification might have taken place during the Middle and Late Miocene [7] .

Paleodietary Inference

Among the various methods of paleodietary inference in primates, dental gross morphology and ultrastructure are useful because teeth are adapted for food processing [32]. Occlusal morphology, which can be quantified by means of shearing crest analysis [9], [11], [33], offers some clues because folivorous apes possess longer shearing crests on molars than frugivorous ones. However, shearing crest quotients are highly dependent on the particular group being analyzed and the baseline used as a reference for comparison [11], [33], so that they might be potentially biased when applied to extinct taxa [34]. Enamel thickness is also generally considered to reflect dietary adaptations to some degree, given the relationship between hard-object feeding and thick enamel [7], [8], [35]–[37]. However, enamel thickness is heavily influenced by phylogenetic constraints [38] and there is no threshold value for distinguishing hard-object feeders on this basis alone [39], [40], so that overall there is no direct relationship between enamel thickness and diet. All these morphology-based approaches reflect dietary adaptation as well as phylogenetic constraints, and hence probably are more informative about what extinct taxa were able to eat than about what they actually ate [41].

Non-morphological methods of paleodietary reconstruction, based on either dental microwear or stable isotope geochemistry, provide more direct information on the properties of the foods consumed independently from adaptation [41], [42]. Geochemical methods, such as stable carbon isotope ratios derived from fossil tooth enamel, are based on the fact that hominoids that consumed grasses and sedges have higher 13C levels than those that fed on fruits and other plants [41]–[46]. These methods are based on the carbon isotopic distinction between C 3 and C 4 photosynthetic pathways. However, C 4 plants (grasses) did not globally expand until the Late Miocene (ca. 8-6 Ma) [47], [48], being present in Eurasia only from 9.4 Ma onwards [49]—i.e., after the extinction of most of the Western Eurasian hominoids studied in this paper. Moreover, isotopic analysis of tooth enamel implies invasive sampling techniques, which are not advisable given the small available dental samples for most of the studied taxa. Dental microwear analysis similarly provides direct evidence on the type of food items consumed by a particular fossil individual, but unlike isotopic methods it is a non-invasive technique, which relies on the microscopic traces left by foods on the enamel surface [10], [15], [50].

Dental microwear analysis is thus one of the most powerful methods for inferring dietary behavior in extinct taxa, being based on the strong and consistent association between dental microscopic patterns and the physical properties of the chewed foods [15], [50]. While both occlusal morphology and enamel thickness might provide important clues as to what types of food a particular taxon was adapted to consume, microwear features directly reflect what an animal actually ate just prior to death [51]. Hence, since the early 1980s dental microwear analysis has been extensively applied to early hominins and other fossil primates in order to try to determinate their dietary behavior (and seasonal changes thereof), as well as tooth use and masticatory jaw movements [12]. Dental microwear provides direct information on the type of food items consumed shortly prior to an individual's death (days, weeks or months, depending on the nature of the foods being masticated)—a phenomenon referred to as the “Last Supper effect” [52]. The physical properties of both the food items (especially phytoliths from plant taxa) and of exogenous grit (abrasive dirt) being ingested during feeding influence dental microwear patterns. Based on both research in the wild [53] and experimental studies [54], [55], some authors have contended that exogenous grit plays an important (or even a primary) role in dental microwear genesis—which might explain why some species have broadly-similar microwear patterns in spite of marked dietary differences [56]. Further experimental research is undoubtedly necessary to better understand the mechanisms responsible of microwear formation, and particularly to determine the role of exogenous grit as a causative agent. However, various studies support the view that food item properties are the main factor determining microwear genesis [57]–[59]. Thus, work on primates and other mammals has shown a strong relationship between dental microwear features and the types of food consumed, as indicated by different taxa from comparable sites, which exhibit microwear differences that are consistent with their contrasting diets [59]–[61].

Dental microwear texture analysis [62]–[65] was recently introduced as an alternative technique to more traditional methods of microwear analysis, being based on 3D surface data and scale-sensitive fractal analysis. Unlike the traditional method, texture analysis does not require the identification of individual features and the analysis is automated—thus being less affected by interobserver error and much less time consuming [51], [62]. Contrary to such advantages, microwear texture analysis is a much more costly alternative, because it relies on white-light scanning confocal microscope instead of 2D micrographs taken with a standard Scanning Electron Microscope (SEM). Texture analysis was introduced to increase repeatability and avoid interobserver error [62], but error studies of traditional microwear quantification techniques show that high errors are found only when different methodologies are employed [66]. As long as a consistent technique is employed, such as that offered by the Microware software package, a common microwear database derived by different researchers can be consistently employed [66]. In this sense, using the traditional microwear analysis approach offers the advantage that our new results can be analyzed together with those derived by previous researches for both the extant comparative sample and other extinct hominoids. Whereas traditional microwear data are available for some Western Eurasian hominoids [10], [12], no microwear texture data have been thus far published for Miocene apes. As a result, the more traditional approach to microwear analysis followed in this work is still currently used by various researchers [34], [67], [68].