Forensic anthropology population data Sacral fusion as an aid in age estimation Luis Rı ´os a, *, Katy Weisensee b , Carme Rissech c a Unit of Anthropology, Department of Biology, Universidad Auto ´noma de Madrid, Madrid 28047, Spain b Department of Anthropology, University of Tennessee, Knoxville, TN 37996, United States c Unitat d’Antropologia Biolo `gica, Departament de Biologia Animal, Vegetal i Ecologia, Universitat Auto `noma de Barcelona, Bellaterra 08193, Spain 1. Introduction The estimation of age-at-death of adult skeletons from both archaeological and forensic contexts constitutes a fundamental problem to be solved by skeletal biologists [1,2]. The age of subadult skeletons may be determined with a low degree of error due to the narrow age ranges associated to dental and skeletal maturation events. In adult skeletons with complete fusion of the epiphyses of the long bones, the preferred method for age estimation is the observation and scoring of bone elements that continue to show epiphyseal activity during the third decade of life (clavicle [3,4], vertebrae [5], ribs [6], iliac crest [7], sacrum [8]). In completely mature skeletons, the degenerative processes that characterize adult age estimation display broader age ranges and greater variation between individuals [9]. The sacrum, specifically the state of fusion of the anterior aspect of the sacral vertebrae, has been used for age estimation in young adults, although few studies have focused on this bone since McKern and Stewart’s original paper [8]. Recently, Belcastro et al. [10], reported the state of fusion of the sacral vertebrae in two documented collections (Sassari and Coimbra). This study widened the age range of the military sample from McKern and Stewart [9], and included a female sample. Also in a recent study [11], the present authors scored the state of fusion of the sacral vertebrae of female and male skeletons in the documented Lisbon collection with the objective of verifying the utility of this bone as an aid in adult age estimation in a forensic context. Results from both research groups are similar and indicate the utility of the sacrum for adult age estimation. The results from the Lisbon sample are presented here along with an application of the current results to a case study; a mass grave from the Spanish Civil War. 2. Material and methods The osteological material comes from the documented skeletal collection housed at the National Museum of Natural History in Lisbon (Portugal), and is mainly comprised of individuals that died between late 19th and early 20th centuries [12]. Female (100) and male (142) individuals between 15 and 59 years of age were selected. The lumbo-sacral transition was examined in every case, and those individuals with variants or anomalies were excluded from the study. Sex and age distribution are shown in Tables 1 and 2. In order to test the results from the Lisbon sample, and from Belcastro et al. [10], the degree of sacral fusion of 21 skeletons exhumed from a mass grave is discussed. Details of the mass grave are given below and in Rı ´os [13]. 2.1. Description of variables The scoring method used by McKern and Stewart [9] was used to score the state of fusion of S 1–2 ,S 2–3 ,S 3–4 , and S 4–5 . The description of the stages is as follows: 0, not fused; 1, fusion has started, less than 1/3 of the segment; 2, fusion in approximately 1/2 of the segment; 3, fusion more than 2/3 of the segment, but it is not completely fused; 4, completely fused. Following Belcastro et al. [10], the frequencies of the pattern of fusion was calculated. For example, an individual with a pattern x444 Forensic Science International 180 (2008) 111.e1–111.e7 ARTICLE INFO Article history: Received 1 May 2008 Accepted 25 June 2008 Available online 15 August 2008 Keywords: Sacrum Age estimation Lisbon collection Mass grave ABSTRACT The degree of fusion at the anterior aspect of the sacral vertebrae has been scored in 242 male and female skeletons from the Lisbon documented collection, ranging from 16 to 59 years old in age. Statistical tests indicate a sex difference towards earlier fusion in young females compared with young males, as well as a clear association between degree of fusion and age. Similar results have been found by other authors in documented skeletal samples from Coimbra and Sassari, and the recommendations stated by these authors regarding age estimation have been positively tested in the Lisbon collection. Although more research from geographically diverse samples is required, a general picture of the pattern of sacral fusion and its associations with age and sex is emerging. We also provide a practical example of the usefulness of the sacrum for age estimation in a forensic setting, a mass grave from the Spanish Civil War. It is concluded that the scoring of the degree of fusion of the sacral vertebrae, specially of S 1–2 , can be a simple tool for assigning skeletons to broad age groups, and it should be implemented as another resource for age estimation in the study of human skeletal remains. ß 2008 Elsevier Ireland Ltd. All rights reserved. * Corresponding author. Tel.: +34 914978146; fax: +34 914978344. E-mail addresses: luis.rios@uam.es, mertibea@yahoo.com (L. Rı ´os). Contents lists available at ScienceDirect Forensic Science International journal homepage: www.elsevier.com/locate/forsciint 0379-0738/$ – see front matter ß 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2008.06.010