Ectopic eruption of a lower permanent molar from the mediaeval necropolis of Alcáçova do Castelo, Mértola, Portugal Inês Leandro a,* , Clara Rodrigues b , Susana Gómez-Martínez b , Cláudia Umbelino a,c a Research Centre for Anthropology and Health (CIAS), University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal b Campo Arqueológico de Mértola (CAM), Rua Dr. António José de Almeida no. 1, 7750-353 Mértola, Portugal c Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal Abstract The mediaeval necropolis of Alcáçova do Castelo is located in Mértola, Southern Portugal, and dates from the 14th to the 16th centuries. The archaeological campaigns started in 1978 and continue today, having yielded more than 759 graves. This report discusses an ectopic tooth eruption observed in skeleton 535, an adult female individual. A distal right permanent lower molar presents an ectopic eruption at the posterior margin of the coronoid process. On the opposite side, the first and second permanent molars are present, the left permanent lower third molar is absent and the mandibular ramus cannot be evaluated since it is broken off and lost. Tooth migration (heteropia) is a common pathological condition documented in clinical literature. However ectopic eruption of lower distal molars is a rare event, and there are few known cases. This is the first case described in archaeological populations worldwide. Keywords: Intraosseous tooth migration Lower distal molar Coronoid process Oral pathology 1. Introduction By definition tooth eruption is the axial or occlusal tooth movement from its intraosseous location within the jaw until it reaches its functional position in the occlusal plane of the oral cavity (Massler and Schour, 1941; Palma et al., 2003; Yaseen et al., 2011). Occasionally, teeth migrate from the eruption site and are found in distant locations from their normal anatomical position (Silva et al., 2007; Wong et al., 2007; Waldron, 2009). The aetiology of this migration is not fully understood (Wong et al., 2007; Wang et al., 2008) and seems to occur most frequently in the mandible with second premolars, canines, and lateral incisors most commonly affected (Silva et al., 2007). The clinical literature has many examples of tooth migration and eruption (Tümer et al., 2002; Suarez- Cunqueiro et al., 2003; Wong et al., 2007; Salmerón et al., 2008; Wang et al., 2008; Goyal et al., 2012; Iglesias-Martin et al., 2012; Payne et al., 2012). However, in the archaeological record only two instances of ectopic eruption have been recorded. A male individual over 45 yearsold, recovered from St. Peters’s Collegiate Church