Age at Death Estimation from Cranial Suture Closures
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 Todds 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.).
Historical Research (A. D. 100-1890)
Todd and Lyon (1924:327) present the following historical account of cranial sutures. Cranial sutures were viewed as controlling both the growth of the brain and, therefore, the shape of the skull. Although classical authors, like Hippocrates, Aristotle and Galen, had observed that some human crania exhibit open sutures, whereas others are almost or entirely devoid of them, the fact that union occurred during life did not appear in the anatomic literature until the works of Gabriele Fallappia (1523-1562), in the middle of the 16th century (Todd and Lyon 1924:327).
Additionally, it was assumed that the condition of the sutures were indicative of racial background (Todd and Lyon 1924:328). For example, in the 1st century A. D., Celsus, in his compendium of medical learning, stated that crania devoid of sutures occur more readily in warm climates [in reference to Ethiopians] (ibid.). Fallappia, best known for his identification of the fallopian tubes, was encouraged by his teacher, Andreas Vesalius (1514-1564), to challenge the classical view that sutures had a close relation with skull morphology (ibid.). One hundred years later, other anatomists had come to agree that this relationship could only be found in rare instances (Todd and Lyon 1924:327).
In 1641, Thomas Bartholin (1616-1680) proposed the following uses for cranial sutures (Todd and Lyon 1924:326): 1) to permit the free transpiration of the vapours in the brain; 2) for the attachment and suspension of the dura matter; 3) for the transmission of fibers of the dura through to the pericranium; 4) for the transmission, in both directions, of vessels carrying nourishment and life to the parts; 5) to diminish the likelihood of fracture of the bones of the skull [Interestingly, Hershkovitz et. al. (1997:397) have once again suggested that open sutures may increase skull efficiency in absorbing related mechanical stresses]; and 6) to permit the penetration of applications from the exterior.
Bartholin asserted that the number and location of the sutures was the same in males and females, and were rarely changed by the shape of the cranium (Todd and Lyon 1924:327). It was proposed that these cranial deformations occurred during fetal development or at birth (ibid.). In the 18th century, anatomists emphasized the analogy between sutural membranes and the diaphyso-epiphseal plane (Todd and Lyon 1924:328). The Hippocratic idea of the relationship between cranial form and suture condition was revived in the 19th century. Since the middle of the 19th century, the growth of the brain has been viewed as a cause, rather than effect, of suture closure (ibid.).
During the 19th century, it was observed that cranial union first occurs in the sagittal suture, and that it occurred earlier within the cranium than upon the exterior (Todd and Lyon 1924:328). In 1856, the anatomist Louis Pierre Gratiolet (1815-1865) proposed a sequence for suture closure and stated that union occurred earlier in negroes. It should be noted that Gratiolet made this distinction in order of cranial closure between higher and lower races of mankind, with negroid races belonging to the lower group (Todd and Lyon 1924:342). [Note: current, politically incorrect terminology has been retained within this paper since its usage is employed within the context of the historic period in which the original studies were carried out]. Gratiolet, observed that ectocranial suture closure progressed sequentially (Todd and Lyon 1924:353): sagittal, lambdoid, then coronal.
Other anatomists began to try to establish an age related sequence for cranial suture closure. For example, in 1861, the physician Paul Broca observed visible sutures in males over the age of 50, and developed a 4 point rating system for cranial suture closure (Todd and Lyon 1924:353). Over time, it came to be accepted that, in the white stock, union began between the ages of 40 and 45 (ibid.). However, in 1869, F. Pommerol noted that the period of union, for each suture, varied across individuals but followed the general pattern (Todd and Lyon 1924:328-329). Pommerol identified the following sequence (ibid.): 1) individuals under 35 years of age had open cranial sutures; 2) around 40 years, the sagittal suture begins to close; 3) around 50 years, the coronal suture begins to close; and 4) by 65 years or more, the temporal suture has finished closing.
In 1885, F. C. Ribbé examined 50 skulls of known age, 40 of which were of white stock , the other 10 presumably non-white (Todd and Lyon 1924:329). He found that the earliest occurrence of cranial suture union was at 21 years and the latest at 55 years. Taking the mean, Ribbé concluded that closure commenced between the ages of 40 and 45, with a standard deviation of 15 to 20 years (ibid.). He stated that ectocranially, sagittal and lambdoid sutures closed before the coronal (Todd and Lyon 1924:355).
In 1888, Schmidt proposed that the basal suture untied between 18 to 21 years, but possibly between 25 and 40 years, and was complete between 40 and 60 years (Krogman 1962:77). In 1890, T. Dwight proposed that before the age of 30, all of the cranial sutures were open (ibid.). Krogman (1962:77) states that Dwight also observed that suture closure began endocranially and occurred later in females than in males (Todd and Lyon 1924:329). Dwight concluded that closure was irregular and, as such, not of value as an indicator of age (Krogman 1962:77). However, his samples consisted of street urchins of indeterminate ages and he did not indicate whether his conclusions referred to internal or external suture closures (Todd and Lyon 1924:329).
Twentieth Century Research
Parsons and Box
In 1905, F. G. Parsons and C. R. Box examined the significance of internal suture closures using 82 male and female skulls of known age (Todd and Lyon 1924:329). They (Krogman 1962:78) concluded that: 1) closure rarely occurred in a healthy skull before the age of 30; 2) between 30 and 50 years of age there is a fair amount of endocranial closure in coronal and sagittal sutures; and 3) over 60, all endocranial sutures were obliterated. Parsons and Box also suggested that less serrated (simple) sutures closed before all other sutures, and that there were no differences in closure periods for the left or right side of the skull (ibid.). They proposed that the lambdoid was the last of the vault sutures to reach complete closure (Todd and Lyon 1924:355). Overall, they concluded that Dwight was justified in his assessment that cranial sutures closed later in females and that cranial sutures were not a good indicator of age (Todd and Lyon 1924:329; Krogman 1962:78).
Frédéric
In 1906, J. Frédéric examined 255 European and 119 non-European crania of known age (Todd and Lyon 1924:329). However, only 91 European and 13 non-European crania of both sexes were opened so that the internal surface could be examined (ibid.). Following Broca, Frédéric introduced his own rating scale of 0 to 4 (open, less than one half closed, half closed, more than one half closed, and totally closed) (Krogman 1962:77-78). Examining endocranial sutures, he found that the lambdoid closed after the sagittal and coronal (Todd and Lyon 1924:355). Frédéric concluded that it was not possible to determine the age of a skull by the condition of suture union closure with any accuracy greater than +/- one decade (ibid.). However, he stated that suture closure occurred later in females, thus concurring with Dwight, Parsons and Box (Krogman 1962:78).
