Age at Death Estimation from Cranial Suture Closures

Sharon N Solomonxerexes@yahoo.com

Dept. of Anthropology

University of Toronto Mar. 2001

Introduction

The texture of a young adult skull is smooth on both the inner and outer surfaces (Krogman 1962:88). Krogman (1962:88) provides the following cranial morphological age sequence: 1) from the age of 25, muscular markings become increasingly evident, especially on the temporal, occipital and on the lateral side of the mandible; 2) around 35 to 45 years, the surface begins to assume a matted, granular appearance; 3) on the inside of the skull, the Pacchionian depressions, both deepen and occur with much more frequency; 4) after the age of 50, the diplöe become less vascularly channeled and there is an increasing replacement by bone. However, there is no consistent age change in the thickness of the cranial bones (ibid.).

The bones of the skull have two layers, the tabula interna and externa, which are separated by a vascular spongy bone space (diplöe)(Krogman 1962:85). These bones are separated by sutures which, in a series, are analogous to the epiphyseo-diaphyseal planes that in both are loci of growth, and that both have a sequence of timing and union (Krogman 1962:76). Just as the epiphyseo-diaphyseal union most frequently begins centrally and proceeds peripherally, so does suture closure begin endocranially and proceed ectocranially (ibid.). In many cases, complete closure will obliterate any signs of the cranial sutures (Krogman 1962:85).

There is a difference however, the epiphyseal union is always complete in normal closures (with the possible exception of the ramal epiphysis of the ischium) whereas suture closure may be incomplete in normal, healthy individuals (Krogman 1962:76). The metopic suture, which is present at birth between the right and left halves of the frontal bone, usually closes around the age of two (Woo 1949:216). However, in some individuals, it is persistent into later adult life. Metopism is more frequent among ?white? and ?Mongoloid? populations (roughly 10% occurrence), compared to a 2% occurrence among ?negroids? (Woo 1949:224).

Forensic anthropologists are frequently called upon to derive as much information as possible from very limited or poorly preserved remains. The method of determining age by cranial suture closure has always been more generally used, due not only to the greater interest in the skull, but because the cranium is frequently the best preserved portion of the recovered skeleton (Brooks 1955:567-568). As such, osteologists have developed numerous techniques which, when applied in concert, increase the accuracy of identification (Lovejoy et. al. 1985:2).

Use of suture closure as an age estimate is predicated upon the hypothesis that suture closure is part of the aging process. However, when suture closure patterns were first studied at the beginning of this century, there were two schools of thought (British and Italian) on this issue (Hershkovitz et. al. 1997:393). The British school maintained that sutural ossification and cranial immobility were normal conditions, whereas the Italian school maintained that they were pathologic in mature human adults (ibid.). In time, probably due to the increasing prominence of the English language in the scientific literature, the British approach toward suture closure became the dominant model in physical anthropology (without actually testing that hypothesis) (Hershkovitz et. al. 1997:394).

The work of Todd during the 1920s provided anthropologists with a framework for estimating age of death from both the pubic symphysis and the cranial sutures (Todd 1924, 1925a, 1925b, 1925c). The use of cranial sutures in estimating (adult) age at death came under criticism during the 1950s. These critiques focused upon Todd?s methodologies, conclusions and the error rates of the method itself (Singer 1953; Brooks 1955; Powers 1962; Krogman 1962). It was noted that the ages obtained from cranial suture closure either produced skewed mortality rates or did not correlate with known age of death (Singer 1953; Brooks 1955). During the 1970s through to the 1990s, several researchers re-examined the use of cranial sutures as a means of determining age at death (Johnson 1976; Meindl and Lovejoy 1985; Masset 1989; Key et. al. 1994; Nawrocki 1998). According to Meindl and Lovejoy (1985:57), this period of investigative research was characterized by a trend in skeletal biology during which it was hoped that one or two highly reliable age indicators would be isolated and perfected.

Despite being used since the 16th century, the use of cranial sutures for determining age at death is regarded by many forensic anthropologists as an overall weak methodology (Meindl and Lovejoy 1985:57). According to Hershkovitz et. al. (1997:395), standard aging methods based on suture closure make use of two arbitrary assumptions: 1) that the different degree of suture closure (usually four stages) represents a normal progressive process, and 2) that different ontogenetic processes operate in different segments of the same suture. Hershkovitz et. al. (1997:395) believe that these assumptions have no factual basis, and that their application is very subjective for the following reasons: the division between segments of the same suture are not clear cut in many skulls, and more than 20% of skulls do not follow the classic pattern of sutural segmentation (ibid.).