The fossil record of large continental vertebrates in Eastern Andalusia is abundant, mainly related to the sedimentary infilling of intramountain Neogene basins (e.g. Aguirre, 1957; Aguirre et al., 1973; Martín-Penela, 1988; Arribas & Palmqvist, 1998; Álvarez-Lao et al., 2009; Arribas et al., 2009; Ros-Montoya, 2010; Madurell-Malapeira et al., 2014; Martínez-Navarro et al., 2018). These basins evolved from marine to lacustrine environments due to the elevation of the Betic Cordillera (e.g. Vera, 1970; Braga et al., 1990, 2003; Viseras, 1991; Fernández et al., 1993; Viseras & Fernández, 1994; Viseras et al., 2003). The high erosion rate of the reliefs favoured the development of fan deltas and alluvial fans in these basins, as well as the development of endorheic basins (Braga et al., 1990; Fernández et al., 1993; Viseras & Fernández, 1994; Viseras et al., 2003; Soria et al., 2003; García-García et al., 2006a, b; Stokes, 2008; Harvey et al., 2018). Some records of large mammals have been traced to Miocene and Pliocene fan deltas (e.g. Reolid et al., 2016; Sendra et al., 2020). These intramountain Neogene basins are related with the Internal Zones of the Betic Cordillera, but the record of large land mammals in the Guadalquivir foreland basin is scarcer and exclusively linked to the Western Guadalquivir Basin (Van der Made & Mazo, 2001; Baena-Escudero et al., 2011).

In this work we report the first record of a proboscidean from the Eastern Guadalquivir Basin related to alluvial fans coming from the outermost mountain front of the Betic Cordillera, and we describe the taphonomic history and conditions that favoured its preservation.

The studied Cuadros outcrop (37º48´19´´N, 3º24´51´´W) is located on the north side of the Sierra Mágina (Betic Cordillera) in Jaén province (Fig. 1). The outcrop is found 1.8 km from Bedmar, along road JV-3222 to Cuadros. From a geological point of view, the outcrop is located by the southern margin of the Guadalquivir Basin, the foreland basin of the Betic Orogen (Fig. 1), whose formation began in the Miocene (García-Castellanos et al., 2002). A transpressive accretionary complex occupies this southern margin, with heterogeneous tectonic units that move over a thick evaporitic sole of Subbetic affinity (Pérez-Valera et al., 2017). Miocene infill consists of marls, sandstones and bioclastic sandstones (García-García et al., 2014). In the Eastern Guadalquivir, where the outcrop lies, marine sedimentation reaches the Early Messinian (Martín et al., 2014).

The alternation of thrust and strike-slip faults together with the abundance of subsoil salt (Pérez-Valera et al., 2017) forms a smooth but varied landscape in the Guadalquivir Valley, with low hills and endorheic and quasi endorheic mini-basins (Ortega el al., 2006). Lakes, many of them saline, were a common feature (López-González et al., 1998). Towards the south, thicker tectonic units of Mesozoic carbonates are structured as a fold-and-thrust belt (García-Rossel & Pezzi, 1975) that results in a mountain range (Sierra Mágina) with peaks above 2000 m high. An intricate mountain front separates the accretionary wedge from Sierra Mágina (García-Tortosa et al., 2008). Frequent and mighty springs drain into the valley at the foot of the mountain front (Gollonet et al., 2002; González-Ramón et al., 2013), where the tributaries of the Guadalquivir are born.

Tectonic activity remains until nowadays (Sanz de Galdeano et al., 2012; Sánchez-Gómez et al., 2014) through large-scale faults and folds that could have controlled the development of subsiding and uplifting areas, favouring either the preservation or the erosion of Quaternary deposits in the Guadalquivir Valley (Pérez-Valera et al., 2012).

The tusk remain is located in a dissected conglomeratic body, part of a lateral alluvial fan developed over the Bedmar valley floor at that time. The approximate height of the top and bottom of this alluvial fan would be respectively 40 and 60 m above the current riverbed (Cuadros river). This height correlates with the two levels of terraces, of +30 and +50 m, attributed to the Middle Pleistocene (300-600 ka respectively; Calero et al., 2008), situated in the Guadalquivir main valley, 50 km away from the Bedmar outcrop. Nevertheless, another tributary stream, 16 km away, has fluvial infilling indicating a humid climate; it reaches terrace levels at +45 m above the riverbed and yields a radiocarbon age of 32-35 ka (García-García et al., 2016). Thus, both ages (Middle to Late Pleistocene) could fit with the age of the alluvial fan deposition.

Sedimentary analysis of the outcrop was carried out in the field with special attention to the beds surrounding the fossil bone. Small fragments of the bone as well as the carbonate sedimentary coating were retrieved. The specimen was not retired from the outcrop.

Four thin sections were prepared to analyse the fabric of the carbonate coating with a Leica M205C at the University of Jaén (Spain), with close observation of the texture and the presence of fossil organic microstructures. Some fragments of this carbonate coating were analysed under Scanning Electron Microscopy (SEM), through secondary electron images with a Merlin Carl Zeiss SEM, at the CICT (University of Jaén).

The Schreger lines of two small fragments were studied. These lines were first defined in the early 19^th century by Bernhard Gottlob Schreger (1800) as a peculiar feature of the Proboscidean dentine (see more details in Espinoza & Mann, 1993). Schreger lines are observed in transversal sections of the tusk, constituting a pattern of two different sets of curved lines that intersect, one in a clockwise direction and the other counter-clockwise. These lines form angles among them, and the set of lines and angles constitutes the “Schreger pattern” (Espinoza & Mann, 1993, 1994; Palombo & Villa, 2001; Ferretti, 2003; Trapani & Fisher, 2003; Lambert, 2005, Ros-Montoya, 2010; Agostini et al., 2012). The Schreger pattern for elephants is characteristic of each species, since their angles are different. This makes it possible to discriminate taxa with a very high reliability. Thus, analysis of the Schreger lines lends valuable support for the taxonomic identification of Proboscidean when the bone remains found in the site are not conclusive (e.g. Mausouss et al., 2014).

Primarily two large fragments were selected and photographed with a high-resolution camera, then the angles between lines were measured using Dino-Lite Pro AM4000 and Photoshop CS6 software, to determine their values and relate them to the taxonomic genus.

The fossil tusk fragment is recorded in detritic sediments evidencing high energy conditions, given the presence of boulders and debris flow. The environment was probably the proximal part of an alluvial fan that formed surrounding the palaeoreliefs of the Sierra Mágina. The potential presence of scavengers as well as surficial water streams favoured the fragmentation, dispersion and transport of remains. Such scenarios are typical for large corpses of vertebrates from terrestrial environments (e.g. Behrensmeyer, 1988). The disarticulated tusk or fragment of tusk would have eventually been transported by the water streams feeding the alluvial fan. In this environment, the surface of the tusk was colonized mainly by mosses and thin microbial mats. Water from the karstic carbonate system of Sierra Mágina favoured the precipitation of carbonate upon the mosses. Therefore, the carbonate coating constitutes a phytothermal bindstone, the porous bands of laminated bindstones of bryophytes alternating with compact laminated bands interpreted as microbial mats.

The carbonate coating played an essential role in the preservation of this vertebrate remain. From a taphonomic standpoint, the growth of mosses around the fragment of the elephant tusk, as well as early carbonate cementation, protected the remains from erosion and weathering. The presence of erosive surfaces within the laminae of the carbonate coating is congruent with a local high-energy environment. However, the growth of mosses and the cementation could have been very fast processes, at a seasonal scale. Subsequent burial by new input of detrital deposits in the alluvial fan determined the preservation.

In view of the average value (106.5º) of the inner Schreger angles of the Cuadros specimen (Fig. 3) and the model by Palombo & Villa (2001; Fig. 3 F), the specimen would coincide with the genus Palaeoloxodon.

The genus Mammuthus presents inner Schreger angles less than 90º and therefore narrower than in the Palaeoloxodon (Fisher et al., 1998; Agostini et al., 2012). The values of the outer Schreger angles of Mammuthus, in the dentine-cementum junction, are higher than the inner Schreger angles (Palombo & Villa, 2001, 2007; Trapani & Fisher, 2003; Agostini et al., 2012). Pawłowska et al. (2014) found Schreger angles reaching 120º in the dentine-cementum junction for Mammuthus. But the Schreger angles measured in the studied specimen are not located at the dentine-cementum junction; they are inner angles, and therefore taxonomic assignation to the genus Mammuthus is discarded.

Analysis of dentinal tubule density for taxonomic determination was discarded due to the fact that the Schreger angles in this case sufficed to identify the genus Palaeoloxodon. According to Agiadi & Theodoru (2005), dentinal tubule density would not present a discriminating power between Mammuthus meridionalis and Palaeoloxodon antiquus, for example. Moreover, previous authors report that the dentinal tubule density may change depending on the distance from the pulp cavity —toward the outer surface of the tusk, the dentinal tubules branch, anastomose and fuse (Agiadi, 2001). Thus, measuring the density of the tubules, at random distances from the pulp would not provide reliable results, just as comparing the Schreger angles of outer and inner positions in the tusk would be insufficient. The use of inner Schreger angles is therefore held to suffice for identifying the studied sample as Palaeoloxodon.

The average value (106.5º) of the inner Schreger angles obtained for the Cuadros specimen (Fig. 3) is coincident with only two different species according to the model proposed by Palombo & Villa (2001; Fig. 3 F): Palaeoloxodon antiquus and Palaeoloxodon falconeri. However, Palaeoloxodon falconeri can be discarded as it is a typical island dwarf proboscidean from Sicily (Romano et al., 2019). The tusk fragment found in the Cuadros outcrop can parsimoniously be said to correspond to Palaeoloxodon cf. antiquus Falconer et Cautley, 1847.

Palaeoloxodon was a genus of the Order Proboscidea (Family Elephantidae) that originated in Africa in the Early Pleistocene and dispersed throughout Central and Southern Europe to Asia during the latest Early Pleistocene, where it rapidly differentiated into various species (e.g. Larramendi et al., 2020). Palaeoloxodon antiquus lived in Europe during the Middle and Late Pleistocene, with a wide distribution and diversification of dwarfed insular descendants (see Larramendi et al., 2020). The earliest occurrence of this straight-tusked elephant in Europe is documented around 600 - 850 Ka (Madurell-Malapeira et al., 2010; Lister, 2015). Its last appearances are post-Eemian, at ∼35 ka (Sousa & Figueiredo, 2001; Mol et al., 2007; Palombo et al., 2010; Athanassiou, 2011; Palombo, 2014) but dwarfed species of the genus Palaeoloxodon inhabiting Mediterranean islands persisted (∼20 ka in Sicily for Palaeoloxodon ex. gr. mnaidriensis; Palombo et al., 2020). P. antiquus showed a broad ecological adaptation, and has been reported from moderate, humid and warm climates (Garutt & Vangengeim, 1982; Stuart, 1991; Konidaris et al., 2018); it lived in forested areas where it fed on leaves, branches and soft grass (Garutt, 1972, 1986).

According to Maslim & Ridwell (2005) and Clark et al. (2006), major climatic changes at a global scale occurred in the latest Early Pleistocene had an important impact on the composition of mammalian assemblages. In the neighbouring Guadix-Baza Basin, numerous sites (Baza-1, Fonelas P-1, Venta Micena, Barranco León, Fuente Nueva-3, Huescar-1) show diverse fauna of the Pliocene to Early Pleistocene, composed by Hyanidae, Felidae, Canidae, Ursidae, Mustelidae, Cervidae, Bovidae, Elephantidae, Equidae, Giraffidae, Rhinocerotidae, Hippopotamidae and Suidae, as well as numerous micromammals (Arribas & Palmqvist, 1998; Arribas et al., 2009; Martínez-Navarro et al., 2010; Rook & Martínez-Navarro, 2010; Medin et al., 2017; Rodríguez-Gómez et al., 2017; Ros-Montoya et al., 2017, 2018; Espigares et al., 2019). The faunal turnover occurring around the Early/Middle Pleistocene transition in Iberia involved the extinction of most of the Early Pleistocene large carnivoran taxa such as the giant hyena Pachycrocuta brevirostris, the sabre-tooth felid Megantereon whitei, the jaguar Panthera gombaszoegensis and the canid Lycaon lycaonoides. Herbivores were also affected, including two horse species, Equus altidens and Equus sussenbornensis (Martínez-Navarro et al., 2009, 2018). Species of African origin arrived at Europe by this time (Martínez-Navarro & Rabinovich, 2011): the spotted hyena Crocuta crocuta, the lion Panthera leo, the leopard Panthera pardus, the auroch Bos primigenius and the straight-tusked elephant (recorded in the Cuadros outcrop) Palaeoloxodon antiquus. At the same time, taxa of Asian origin, such as the steppe mammoth Mammuthus trogontherii, the deer Cervus elaphus, an Indian bovid Hemibos galerianus, and the horse Equus ferus, among others, reached Iberia (Martínez-Navarro et al., 2009; Madurell-Malapeira et al., 2010).

In comparison with the neighbouring Guadix-Baza Basin, the record of large Middle Pleistocene mammals recorded in the Solana del Zamborino outcrop (Fonelas) comprises Felidae (Felis, Lynx and Panthera), Canidae (Canis and Vulpes), Cervidae (Capreolus, Cervus, and Dama), Bovidae (Bison and Bos), Elephantidae (Mammuthus and Palaeoloxodon), Equidae (Equus), Rhinocerotidae (Stephanorhinus), Hippopotamidae (Hippopotamus), Suidae (Sus) and Cercopithecidae (Macaca) (Botella-López et al., 1976; de Porta, 1976; Alberdi & Ruiz-Bustos, 1985; Martín-Penela, 1983, 1988).

The Middle Pleistocene examples of Palaeoloxodon antiquus in South Spain have been reported from fluvial terraces along the Western Guadalquivir Basin by the localities of La Rinconada, Hornachuelos, and Almodóvar del Río in Sevilla and Córdoba provinces (Van der Made & Mazo, 2001; Baena-Escudero et al., 2014; Table 1). Moreover, Cortes-Sánchez et al. (2017) reported this specie from the Cave of El Pirulejo (Córdoba province). In the Granada Basin, P. antiquus has been identified from the Middle Pleistocene of a Loja outcrop (Ros-Montoya, 2010; Table 1). The eastern record of P. antiquus in South Spain pertains to the Guadix-Baza Basin (Granada province) by the Solana de Zamborino outcrop (Table 1; Martín-Penela, 1988). The P. cf. antiquus recorded from the Cuadros outcrop is 47 km North of Solana de Zamborino and would be easily connected with the Guadix-Baza Basin through the strait between Sierra Mágina and Sierra de Cazorla relief, which constituted the gateway to the Guadalquivir Basin. Therefore, the record of Palaeoloxodon cf. antiquus from the Cuadros outcrop connects the populations of P. antiquus from the Western Guadalquivir Basin with those of the Guadix-Baza Basin. Seasonal migrations between low lands of the Western Guadalquivir Basin (outcrops at 10 - 200 m above sea level), and high lands of the Granada Basin (outcrops at 500 - 600 m) or the Guadix-Baza Basin (outcrops at 900 - 1200 m) are not discarded. The studied outcrop, 550 m high, lies potentially along the way from the Guadalquivir Basin to the Guadix-Baza Basin. In this sense, African elephants (Loxodonta africana) present seasonal movements related to vegetation dynamics, in turn ruled by dry and wet conditions (e.g. Wittemyer et al., 2007; Wall et al., 2013; Bohrer et al., 2014).

The age of the alluvial fan where the studied tusk remain was recorded is inferred from comparisons with terraces of Guadalquivir and other tributary streams, ranging from 600 to 32 ka (Middle to Late Pleistocene). However, the fact that the record of P. antiquus in South Spain is reported exclusively from the Middle Pleistocene in the Western Guadalquivir Basin, Granada Basin and Guadix-Baza Basin (e.g. Martín-Penela, 1988; Van der Made & Mazo, 2001; Ros-Montoya, 2010; Baena-Escudero et al., 2014) leads us to infer a Middle Pleistocene age for the alluvial fan. Still, we cannot totally discard a Late Pleistocene age for this fossil remain.

This work reports the first record of an elephantidae from the eastern sector of the Guadalquivir foreland Basin (Jaén province). The remain was retrieved from conglomerates deposited in the alluvial fans downslope of the outermost mountain front of the Betic Cordillera, more precisely from Sierra Mágina. These fans developed during the Middle to Late Pleistocene, associated with an intense erosive phase of the young reliefs of the mountain front.

The remain is a fragment of a fossil tusk (74 cm length) associated with high energy detritic sediments ranging from coarse sands to boulders, transported by water streams at the foot of the mountains. The fossil bone is mostly coated by a carbonate-laminated crust (< 2 cm). Its detailed analysis under thin section and SEM evidences a porous laminated fabric of phytal appearance (clusters of multibranched stalks). These structures are interpreted as fossil bryophytes. Therefore, the disarticulated tusk would have been transported and probably fragmented by surficial water streams in a high energy context. The surface of the tusk was covered by mosses that cemented early on. This carbonate crust surrounding part of the tusk favoured its preservation in a high-energy environment, while preservation was likewise aided by fast burial.

The analysis of the Schreger lines in the internal structure of the tusk allows us to assign this remain to the straight-tusked elephant Palaeoloxodon cf. antiquus. This taxon has been reported from the Middle Pleistocene of the Western Guadalquivir Basin (Sevilla and Córdoba provinces) and neighbouring basins such as Granada Basin and Guadix-Baza Basin (Granada province). Consequently, the specimen studied in the southeastern Jaén province (Eastern Guadalquivir Basin) would connect the populations of P. antiquus from the Western Guadalquivir Basin and the Guadix-Baza Basin. Seasonal migrations between low lands of the Western Guadalquivir Basin and high lands of the Guadix-Baza and Granada basins are not discarded.