Hershkovitz et. al

In 1997, Hershkovitz et. al. examined the extent of the sagittal suture closure in 3,636 skulls from the Hamann-Todd and Terry collections (Hershkovitz et. al. 1997:393). The sagittal suture was chosen (Hershkovitz et. al. 1997:395)

as it is the only ‘end-to-end’ type suture in the calvaria (avoiding ‘‘pseudoclosure’’ due to overlapping of bone, as in frontal over parietal bone), and because its location at the midline neutralizes it from biomechanical influences.

Hershkovitz et. al. (1997:395) identified five sutural conditions, defined as: 1) totally closed (TC): no signs of the sagittal suture were observed on the ectocranial surface, from bregma to lambda; 2) partially closed (PC): less than 10% of the suture length was open; 3) totally open (TO): the suture line was clearly visible with almost no interruptions along its entire length, from bregma to lambda. Minor closure at the area of the parietal foraminae was ignored; 4) partially open (PO): between 10% and 90% of the suture length was open; and 5) premature suture closure (PMSC). PMSC was distinguished from pathological closure, which occurs very early in life (5 years or earlier), and which is characterized by sutural ridging (i.e., scaphocephally) (Hershkovitz et. al. 1997:395). In the PMSC category all skulls in which the sagittal suture was closed after the age of 5 years but before 18 years, were included (ibid.).

Hershkovitz et. al. (1997:398) provide the following conclusions: 1) the sagittal suture cannot be used for aging the skeleton; 2) although cross-sectional in nature, suture obliteration patterns are not temporary progressive stages on an age scale, but rather independent permanent phenomena; 3) some suture closure patterns are genetically inherited; 4) females and males manifest different suture closure patterns; 5) in all ages, the relative frequency of the ‘‘totally open’’ category is higher in females than in males; 6) the medical conditions (HFI, TB) examined in the present study are not associated with a suture closure condition; and 7) suture closure is neither a pathological phenomenon nor the result of normal aging process. Taken as a whole, the authors state that reliance upon cranial suture closure for age estimation is of no value for either forensic application or paleodemography studies (Hershkovitz et. al. 1997:397).

Conclusion

All of the previous anatomic studies of cranial sutures, prior to the work of Todd and Lyon in the 1920s, assumed that the appearance of these provided information of racial background, sex, age and intelligence. While these early studies attempted to examine as many crania as possible, from a variety of sources, there was no method to verify the reliability of ‘known’ age at death. Todd and Lyon (1925:35) stated that their work differed from all earlier studies in that they sought to establish a definite age relationship for suture closure, whereas earlier researchers, dealing with a number of crania of unknown and various ages, based their observations solely upon a general average which was termed a ‘closure tendency’. Moreover, it would be apparent that closure tendency would differ with every collection of crania, especially if one merely notes the occurrence of ectocranial sutures (ibid.).

Todd and Lyon (1924, 1925a, 1925b, 1925c) found no onset timing differences between endocranial and ectocranial closure, although endocranial closure was deemed to be more reliable since there were more occurrences of lapsed union in ectocranial sutures (Krogman 1962:81-82). They found no racial differences nor differences between the left and right sides of the skull (Todd and Lyon 1924:370). The assumption that anomalous closure of one suture correlated with anomalous closure of all sutures in a given skull became the basis of all future criticisms of the Todd and Lyon methodology. Since Todd and Lyon specifically eliminated ‘abnormal’ crania from their experimental sample, it should not be surprising that attempts to replicate their findings, using random samples which include such crania, should fail (Meindl and Lovejoy 1985:58).

Since the initial studies by Todd, there has been several changes in how published research is presented. First, when presenting supporting background information, Todd provided a detailed historical account as to both who conducted the study and how that research was conducted. Later studies merely provide a collection of references, with one or two notations as to the relevance of the previous study. Second, Todd provided a detailed account regarding the criteria of both how his sample was obtained and why certain crania were rejected from the final study (listing both catalogue numbers for each crania and a detailed account of any anomalies).

Third, Todd published his raw data as well as the ‘adjusted’ curve graphs. Later studies only publish results which have already been ‘adjusted’, or simply provide a text summary of the findings. Finally, one of the major changes in methodologies from Todd’s initial work, is the dependence upon random sampling, multivariate and regression analysis. In examining these studies, it seems, at face value, that this embracing of statistical methodologies has clouded the central issue, specifically, can cranial sutures provide a valid estimation for age at death?

As mentioned previously, Todd and Lyon eliminated aberrant skulls from their examination in order to produce a standard for estimating age at death. It seems surprising that later researchers attempted to incorporate deviant findings into averaged results. As stated in the conclusion of the 1924 paper, cranial suture closure, especially when employed in conjunction with other age markers in the post cranial skeleton, can provide an estimate of age at death within one decade of the ‘actual age at death’.

References

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