Revisión de la mandíbula humana de Bañolas, Gerona, España

Abstract

Since the discovery of a fossil human mandible in 1887 near the city of Bañolas (Gerona, Spain), there has been considerable disagreement among scholars as to its taxonomic allocation. In different studies the specimen has been included within Homo neanderthalensis {King, 1864} (Hernández-Pacheco & Obermaier, 1915; Sánchez, 1993), ante-Neandertals (de Lumley, 1971-72) or an ante-würmian (Roth & Simon, 1993) species. More recently, the Bañolas mandible has been argued to lack derived Neandertal traits (Daura et al., 2005). Although the mandible was found in a quarry of travertine, its exact location is unknown. Some patches of travertine adhered to the specimen have provided a geochronological age range between 17,6 to 110 kyr (Berger & Libby, 1966¸ Yokoyama et al., 1987; Julià & Bischoff, 1991; Grün et al., 2006). The only direct dating of the mandible yielded an age of 66 ± 7 kyr B.P. (Grün et al., 2006). After a recent examination of the original specimen, a number of morphological traits of this mandible has been described and compared with information from the literature regarding H. heidelbergensis {Schoetensack, 1908}, H. neanderthalensis and both fossil and extant H. sapiens {Linneo, 1758} mandibles. These characters have been considered to be of taxonomical significance to discriminate between these three species (see below for references). Despite the fragmentary condition of the Bañolas mandible, a considerable number of morphological traits can be evaluated: presence/absence of the mental trigone (Schwartz & Tattersall , 2000), shape of the anterior basal corpus (Quam & Smith, 1998), position of the digastric fossa (de Lumley, 1973), number, size and location of the mental foramen (Trinkaus, 1993), presence/absence of the retromolar space and inclination of the retromolar triangle (Franciscus & Trinkaus, 1995; Rosas, 2001), shape of the mandibular foramen (Smith, 1978), size and shape of the medial pterygoid tubercle (Antón, 1996), relative position between the condyle and the ascending ramus plane (Rosas, 2001; Nicholson & Harvati, 2006; Trinkaus, 2006), dimensions of the submental incisure (Mounier et al., 2009), location and trajectory of the mylohyoid line (Mounier et al., 2009), size of the alveolar plane (Mounier et al., 2009), shape of the gonion (Creed-Miles et al., 1996) and relative position of the lateral prominence to the dentition (Rosas, 2001; Mounier et al., 2009). The state of these characters in the Bañolas mandible is as follow: absence of mental trigone (but slight evidences of a possible mental fossa and a possible central keel) (Fig. 1), triangular anterior basal corpus shape (Figs. 1 and 3), disgastric fossa located in the posterior face of the symphysis (Figs. 1 and 3 ), a single small mental foramen placed in the upper half of the corpus and below the P4 (Fig. 2), absence of retromolar space and an oblique retromolar triangle relative to the alveolar margin (Figs. 2 and 6), small and not lib-shaped medial pteriogoid tubercle (Fig. 5), medially placed condyle relative to the ascending ramus plane (Fig. 4), large dimensions of the submental incisure (Fig. 2), mylohyoid line that starts near the M3 and follows obliquely to the alveolar margin (Fig. 4), not large (wide) alveolar plane (Fig. 6), rounded (not truncated) gonion (Figs. 2 and 4) and anteriorly placed lateral prominence (M2 and M2/ M3 septum) (Fig. 2). Regarding the mandibular foramen, it seems to present a lingula, it could confirm the presence of a normal mandibular foramen type and it would discard the possibility of an H-O mandibular foramen type (Smith, 1978) (Fig. 5). Except for the large submental incisure and the absence of mental trigone, the state of all these characters is more frequent in Homo sapiens specimens (de Lumley, 1973; Smith, 1978; Trinkaus, 1993; Franciscus & Trinkaus, 1995; Antón, 1996; Creed-Miles et al., 1996; Quam & Smith, 1998; Rosas, 2001; Nicholson & Harvati, 2006; Trinkaus, 2006; Mounier et al., 2009). The large submental incisure is a characteristic trait of Homo heidelbergensis and the absence of mental trigone is a plesiomophic character shared by Homo neanderthalensis, Homo heidelbergensis and some upper Pleistocene Homo sapiens individuals (Schwartz & Tattersall , 2000). On the view of this work our conclusion is that the Bañolas mandible shows neither derived Neandertal traits nor clear affinities to H. heidelbergensis. On the contrary, this specimen bears a greater resemblance to the H. sapiens mandibles.