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

Bolk, L. 1915 On the premature obliteration of sutures in the human skull. American Journal of Physical Anthropology 17:495-523.

Brooks, S. T. 1955 Skeletal age at death: Reliability of cranial and pubic age indicators. American Journal of Physical Anthropology 13:567-597.

Buikstra, D. and D. H. Ubelaker (eds.) 1994 Standards for Data Collection from Human Skeletal Remains. Arkansas Archaeological Survey Research Series, No. 44.

Hershkovitz, I., Latimer, B. , Dutour, O., Jellema, L. M. ,Wish-Baratz, S. and Rothschild, C. 1997 Why do we fail in aging the skull from the sagittal suture? Journal of Physical Anthropology 103:393-399.

Hrdlicka, A. 1939 Practical Anthropometry. Wistar Institute, Philadelphia.

Johnson, J. S. 1976 A comparison of age estimation using discriminate function analysis with some other age estimations of unknown skulls. Journal of Anatomy 121:475-484.

Key, C. A., Aiello, L. C. and Molleson, T. 1994 Cranial suture closure and its implications for age estimation. International Journal of Osteoarchaeology 4:193-207.

Krogman, W. Milton 1962 The Human Skeleton in Forensic Science. Charles C. Thomas, Springfield, Ill. pp. 76- 91.

Lovejoy, C. O., Meindl, R. S., Mensforth, R. P. and Barton, T. J. 1985 Multifactorial determination of skeletal age at death: A method and blind tests of its accuracy. American Journal of Physical Anthropology 68:1-14.

Masset, C. 1989 Age estimation on the basis of cranial sutures. In Age Markers in the Human Skeletal. Iscan, M. Y. (ed.). pp. 71-103.

Meindl, R. S. and Lovejoy, C. O. 1985 Ectocranial suture closure: A revised method for the determination of skeletal age at death based on the lateral anterior sutures. American Journal of Physical Anthropology 68:57-66.

Nawrocki, Stephen P. 1998 Regression formulae for estimating age at death from cranial suture closure. In Forensic Osteology: Advances in the Identification of Human Remains (2nd ed.) Reichs, K. J. (ed.). Charles C. Thomas, Springfield, Illinois. pp. 276-292.

Powers, R. 1962 The disparity between known age and age as estimated by cranial suture closure. Man 83:52-55.

Saunders, S. R., Fitzgerald, C. Rogers, T., Dundar, C. and McKillop, H. 1992 A test of several methods of skeletal age estimation using a documented archaeological sample. Canadian Society of Forensic Science Journal 25:97-118.

Singer, R. 1953 Estimation of age from cranial suture closure: A report on its unreliability. Journal of Forensic Medicine 1:52-59.

Todd, T. W. and Lyon, D. W. 1924 Endocranial suture closure, its progress and age relationship: Part I Adult males of the while stock. American Journal of Physical Anthropology 7:325-384.

1925a Cranial suture closure, its progress and age relationship: Part II Ectocranial closure in adult males of the white stock. American Journal of Physical Anthropology 8:23-45.

1925b Cranial suture closure, its progress and age relationship: Part III Endocranial closure in adult males of Negro stock. American Journal of Physical Anthropology 8:47-71.

1925c Cranial suture closure, its progress and age relationship: Part IV Ectocranial closure in adult males of Negro stock. American Journal of Physical Anthropology 8:149-168.

Woo, Ju-Kang 1949 Racial and sexual differences in the frontal curvature and its relation to metopism. American Journal of Physical Anthropology 7:215-226.

Meindl and Lovejoy

In 1985, Meindl and Lovejoy re-examined the Hamann-Todd Collection. They chose 10 ectocranial landmarks, although it is unclear whether they scored for bilateral expression (Meindl and Lovejoy 1985:60). They employed the following scoring methodology: 0 - no observable closure; 1 - 1 to 50% closure; 2 - 51 - 99% closure; 3 - 100% closure. Small (1 cm) lengths of a suture or specific sites were selected for inspection, for which only the judgment of one observer was required (Meindl and Lovejoy 1985:58). Since they proposed that in the case of forensic anthropology, the regularity of closure during the early adult years was not critical, only ectocranial sutures were studied (ibid.). Meindl and Lovejoy (1985:58) thus chose 17 ectocranial points for 236 crania from the Hamann-Todd collection, based upon the reliability of stated age at death.

During the initial analysis, they found that some of these landmark sites were of limited value for consistent age determination (Meindl and Lovejoy 1985:58). These sites were as follows (Meindl and Lovejoy 1985:58-60): (closure of) 1) parieto-mastoid; 2) squamosal point; 3) occipito-mastoid; 4) zygomatic and malar; 5) frontolacrimal; and 6) frontoethmoid. The sites which were retained (Meindl and Lovejoy 1985:60) were the vault system (midlambdoid, lambda, obelion, anterior sagittal, bregma, midcoronoal and pterion) and lateral anterior system (midcoronoal, pterion, spheno-frontal, inferior sphenotemporal and superior sphenotemporal). Meindl and Lovejoy (1985:60) found a chronological age ranking at the pterion, sphenofrontal, midlambdoid and lambdoid, respectively. These were based upon the assumption of underlying continuity of ordinal closure scales (the Kendall coefficient) (ibid.).

The next phase of analysis, to determine combination of sites which could be employed in age estimation, was based upon the following assumptions (Meindl and Lovejoy 1985:61): 1) sutures should demonstrate a protracted sequence of closure; 2) sutures should correlate with age during the primary period of its closure activity; and 3) the information provided by each suture should be specific to that particular suture. From these criteria, and since the calotte is usually the most durable in archaeological populations, they determined that the 5 lateral anterior sites were the best overall predictor of age (Meindl and Lovejoy 1985:61). It was assumed that the sample crania would exhibit a commencement and termination sequence which correlated with long bone epiphyseal fusion sequence (Meindl and Lovejoy 1985:62).

Using composite scores for each sample specimen, they found that the lateral anterior sites closed in the following sequence: Commencement - pterion, midcoronal, sphenofrontal, inferior sphenotemporal, superior sphenotemporal; Termination - pterion, sphenofrontal, midcoronal, inferior sphenotemporal, superior sphenotemporal (Meindl and Lovejoy 1985:63). The vault sutures closed in the following sequence: Commencement - obelion, pterion, anterior sagittal, lambda, midlambdoid, midcoronal, bregma; Termination - obelion, pterion, anterior sagittal, lambda, bregma, midlambdoid, midcoronal (ibid.). The overall (linear) correlation with known age was 0.57 for lateral anterior sites and 0.50 for vault sutures (ibid.).

It was found that the average mean deviation, for lateral anterior scoring, was 7.5 years, and 14.2 years for vault sutures (Meindl and Lovejoy 1985:64). Meindl and Lovejoy (1985:64-65) also examined whether or not race or sex had any effect on suture closure, thus affecting the accuracy of age prediction. Using analysis of covariance (ANCOVA) on the residuals, they found no measurable influence of either race or sex (ibid.). However, Meindl and Lovejoy (1985:62) state that any age estimation should take into account postcranial indicators as a control for suture cranial variations.

Buikstra and Ubelaker

In Standards for Data Collection from Human Skeletal Remains, Buikstra and Ubelaker (1994) proposed combining several aging methods, based on different cranial sutures (Baker 1984; Mann et. al. 1987; Meindl and Lovejoy 1985; Todd and Lyon 1924, 1925a, 1925b, 1925c) to predict age. According to Hershkovitz et. al. (1997:394), this ‘refined’ method ignored the fact that correlation between the recommended areas for inspection, along the cranial sutures, and age are very low. They (Hershkovitz et. al. 1997:394) proposed that these new standards still turn out old results, which seems to be apparent in their own research of cranial suture closure.

Nawrocki

In 1995, Nawrocki examined all three categories of sutures (ectocranial, endocranial and palatine) using regression and analysis of variance techniques (Nawrocki 1998:276). He studied 100 individuals of known sex, age and race (black/white) from the Terry Collection. Two individuals were chosen from each race/sex category in every half decade, ranging in age from 21-85 years (Nawrocki 1998:277). Although, for whites, the lowest age was 27. No specimens were excluded for any reason, barring damage therefore there was no control when examining ‘abnormal’ skulls (ibid.). Following Meindl and Lovejoy (1985:60), 27 landmarks were scored on each skull: ectocranial (16), endocranial (7), and palate (4) (Nawrocki 1998:278). Both the left and right side of the skull were scored when bilaterally expressed (ibid.).

A second sample was obtained in order to test the results from the Terry sample. This consisted of the crania of 61 white individuals (27 males; 34 females), aged 58-102 years, obtained from medical dissection rooms in Syracuse and Indianapolis (Nawrocki 1998:279). However, while Nawrocki (1998:279) notes that the presence of soft tissues and saw cuts on the cranial vault, limited suture observations of the endo and ectocranial surfaces, he does not indicate how the age at death of the sample crania was verified.

In order to produce a score, all 27 landmarks were added together, resulting in a range of 0-81 (Nawrocki 1998:279). It was found that there was a moderately strong correlation between the predicted age and the age of the Terry samples (Nawrocki 1998:279). However, Nawrocki (1998:281) does note that summing or averaging the data will result in a loss of information. One area of possible concern, regarding this reliance upon linear regression models, is that it allows for a predicted range from 25.3-82.8 years, even though the sample crania were 58-102 years old (Nawrocki 1998:279). Additionally, when tested against the Terry samples, the predicted ages deviated, on average, between 9 to 21 years (Nawrocki 1998:286). It should be noted that Todd’s average age deviation was 6 years, which he deemed to be unacceptable.

Creating an equation to test Meindl and Lovejoy’s proposal that race or sex may affect suture closure rates, Nawrocki found that there was a correlation between suture closure and sex, but not race, although there was an interaction between race and sex (Nawrocki 1998:282). He suggests that this finding, which is contrary to that of Meindl and Lovejoy, is due to the use of more cranial landmarks (ibid.). Nawrocki (1998:282) created 8 different equations to test each case sample, although this required dropping the number of landmarks from 27 to 15.

In his conclusion, Nawrocki (1998:288) proposes two possible sources of error: sampling (random) and secular trends (non-random). Sampling error is said to occur when the two parent populations are similar overall, yet the test sample is drawn unevenly (ibid.). However, this seems to be a rather weak argument, considering the emphasis placed on obtaining ‘random’ samples for statistical analysis. Secular trends systematically change the nature of the second population, or portions of it, so that the regression derived on the first are no longer as accurate (Nawrocki 1998:288). In this instance, one is concerned that the sample is too randomly varied. In other words, researchers seem to prefer finding fault with the ‘sample’ rather than with their chosen methodology.

Cattaneo, Cobb and Singer

In 1937, Cattaneo studied 100 ‘miscellaneous’ Argentinean skulls, and stated that suture closure could only provide a suggestive age indicator (Krogman 1962:86). Hrdlicka (1939 cited in Krogman 1962:86) stated that endocranial suture closure was only reliable within ten years on either side of the predicted age. Cobb (1952:840 cited in Krogman 1962:86), using the Todd and Lyon methodology, stated suture closure was only reliable within nine years on either side of the predicted age. In 1953, R. Singer concluded that using cranial sutures as an estimation of age at death was an unreliable assessment methodology (Krogman 1962:86). He found that there is a tendency for the cranial sutures, of both females and males, to either remain open throughout life or to close much earlier than predicted by Todd’s method (Singer 1953:56).

Brooks

In 1948, S. Brooks, at the suggestion of Dr. McCown of the University of California, begun an inquiry into why samples of aboriginal California Indians showed a mean age at death consistently under 30 years (Brooks 1955:568). The method employed attempted to employ Todd’s methods of age determination, using both cranial suture closure and changes to the pubic symphysis, to see if they were applicable to races other than white and negro, and to determine the correlation of these two methods when applied to one individual (Brooks 1955:568). However, Brooks (1955:571) attempted to examine the cranial sutures and pubic symphysis in isolation from the rest of the skeleton, as single variables, which, according to Todd and Lyon (1924) is neither a reliable nor valid methodology.

In 1948, just under 400 individual skeletons from the University of California collection were selected for testing (Brooks 1955:569). In 1950, the some of the skeletons employed by Todd from the Hamann Museum collection were used for review (ibid.). Later, in 1953, a second series of 70 skeletons were analyzed to verify the methodology (ibid.). The sample was chosen based on the following criteria: 1) the individual be over 18 years of age, as judged by long bone epiphysis-diaphysis union and fusion of the three elements of the acetabulum; 2) the crania vault must contain at least the area of the coronal, sagittal and lambdoid sutures; and 3) the symphyseal surface of at least one pubic bone must be preserved (Brooks 1955:569). It should be noted that all of the skeletons were from California, but no consideration was made of area or archaeological horizon (ibid.).

Sex determination was based upon: 1) the ischio-pubic index, wherever possible; 2) breadth of the sciatic notch; 3) subpubic angle; and 4) the general morphology of the skull and mandible (Brooks 1955:570). Following the criteria of expected suture closure set out by Todd (1924; 1925a, 1925b, 1925c), Brooks employed a 5 point scale (0 - open to 4 - complete closure) (Brooks 1955:570). She (Brooks 1955:571) stated that there was “no way of checking the accuracy of either cranial or pubic ages, should they be divergent in one individual, except by indirect approach.”

Brooks (1955:573) found that, for females, there was a “sharp deviation” for the predicted age at death between cranial suture and pubic symphysis methods, of at least 10 years. She states that cranial suture closure tends to lag anywhere from 5 to 25, with a mean of +/- 9 years, behind that of the pubic symphysis (Brooks 1955:573). The male sample showed a deviation from 5 to 8 years, with a mean of +/- 2 years, between cranial suture and pubic symphysis methods (Brooks 1955:574). Brooks found that in cases where all of the sutures were open (predicted age <25),>

McKern and Stewart

In 1957, McKern and Stewart revised the cranial suture closure methodology (Krogman 1962:82). Following the work of Singer (1953), they assigned four parts to the coronal and sagittal sutures and three to the lambdoidal sutures, but followed Todd and Lyon in the five scale rating system (0-4, but 2-3 are combined) (Krogman 1962:82). However, their observations were based solely upon ectocranial suture closure (Krogman 1962:83). McKern and Stewart (1957) noted that closure tends to begin the the 1st and 4th parts of the coronal, 1st part of lambdoid, and 1st and 4th parts of the coronal (ibid.). The final stage of closure tends to be in the 1st and 2nd parts of the sagittal, 1st or 2nd part of lambdoid, and the 1st part of the coronal (ibid.). Although they found that there was an age progression in the uniformity of suture closure, they believed that it was too erratic to be of use in determination of age at death (McKern and Stewart 1957:37). McKern and Stewart (1957:37) concluded that:

So erratic is the onset and progress that an adequate series will provide just about any pattern at any age level. Thus, as a guide for age determination, such a trend is of little use.

Genovese and Messmacher

In 1959, Genovese and Messmacher studied 101 Mexican male skulls of all ages and known identity: 47 ‘indigenas’ and 54 ‘mestizos’ (Krogman 1962:87). They found that the age difference between suture estimation and actual age was 12 years, 11 months (indigenas) and 9 years, 5 months (mesitzos) (ibid.).

Todd and Lyon

The research of Todd and Lyon (1924, 1925a, 1925b, 1925c) provided the groundwork for all North American forensic and physical anthropological studies for the remainder of the 20th century. In 1924, Todd and Lyon proposed to “present the facts concerning suture closure and its relation to the racial form and individual contour of the brain case”(1924:326). The research by Todd and Lyon (1924, 1925a, 1925b, 1925c) was the first new attempt to estimate age using endo and ectocranial suture closure since Pommerol, Ribbé, Frédéric, Parsons and Box, with the specific aim to create a precise numerical rating system for cranial closure (Krogman 1962:78). Todd and Lyon (1924:355) state that:

Until we gathered the accurately dated material in the Hamann Museum, no one possessed a sufficient collection of skulls of known age to justify the interpretation of suture closure upon its age relationship.

Todd and Lyon (1924, 1925a, 1925b, 1925c) tried to ensure that the skeletal material was large enough to justify it as a sample of the population under study. In addition to sex and race, verifiable age at death had to be known and the crania had to be cut, so that examination of the interior surface was possible. Todd and Lyon (1924:330) initially examined the crania of more than 1,000 individuals, from which those of which were of uncertain known age, and did not have a complete post cranial skeletal for comparative study were rejected. Of the original 1000 specimens, 514 crania of known age were examined (ibid.): 307 crania of white males, 58 white females, 120 negro males, and 29 negro females. From this initial sample, 40 white skulls (13.3%) and 41 (34.2%) were excluded as anomalous (Krogman 1962:79).

Todd and Lyon (1924, 1925a, 1925b, 1925c) provide detailed accounts explaining both which skulls (by catalogue number and age) were rejected, and pertinent cranial features which led to the rejection. Rejections were based upon: 1) whether or not the skull belonged to skeletons belonging to the symphyseal anthropoid strain (Todd and Lyon 1924:339-340):

It is characteristic of the anthropoid strain that the pubic age relationships fall nearer to those of the Giant Anthropoids, and there is a clear difference in age relationship of the skeleton between human beings according, as they exhibit the anthropoid strain or the regressive form of symphysis. In the first place, elimination based on the anthropoid strain in the pubic symphysis affects skeletons of the third decade.2) precocious union; 3) no endocranial closure of vault sutures; 4) evidence of dwarfism; and 5) no endocranial closure of any cranial sutures. As stated by Todd and Lyon (1924:348), they were confident in their rejections because they were able to examine the entire skeleton and they were cross referenced with legal documentation of age at death.

Todd and Lyon (1924:331) state that

from the point of view of age determination, the Western Reserve University collection is dependably so far as is humanly possible and much more dependable than the vital statistics upon which actuarial investigations for insurance companies are based.

The age of the specimens ranged from 18 to 84 years (Todd and Lyon 1924:338). Todd and Lyon state that this relatively small sample size was statistically accurate, since the objective of the study was to determine the progress of cranial suture union (ibid.). They note that in certain instances, they observed that sutures seemed to fail to completely close (Todd and Lyon 1924:337). This condition was defined as ‘lapsed union’ of the suture. They defined it as the incomplete union of the suture, characterized by a build up of bone tissue along the edges of the unclosed part (ibid.). Todd and Lyon (1924:337) classed incidents of lapsed union as closed, since a suture in this condition would be unlikely to close to any great extent.

Following the precedent set by anatomists of the seventeenth century, Todd and Lyon (1924:336) grouped the sutures in the following manner: vault [sagittal (and metopic), coronal and lambdoidal]; accessory [spheno-frontal and spheno-parietal]; and circum-meatal [spheno-occipital]. For later decades, they eliminated skulls which exhibited partial or complete closure of the sagittal and masto-occipital at an early age (ibid.). They adopted Broca’s arrangement of complication of sutures, degrees of closure and subdivision of particular sutures, except for the adoption of Frédéric’s inversion of Broca’s categorization of the amount of suture union (i.e. 0 = no union and 4 = complete closure; 1 to 3 refer to the amount of union - one quarter... three quarters). They did not differentiate between union which had progressed halfway along a suture and closure which involved a total of half the length of a suture, but is exhibited in separate, discrete areas (Todd and Lyon 1924:336).

The following information was recorded, as the joint observation of two individuals (Todd and Lyon 1924:331-332): sample crania number, race, sex, age, greatest length, greatest breadth, cephalic index, cranial capacity and sites of Wormian bones. The observations were only accurate for the external and internal surface of the crania, with no accurate information regarding suture conditions within the skull wall (ibid.). The closure for each suture was then averaged and plotted. Todd and Lyon (1924:333) state that in spite of individual differences, there was a definite trend in the progress of suture closure in relation to age.

Todd and Lyon (1924:333) then repeated the above procedure with the male negro and female crania (of both ‘racial stocks’). This led to the elimination of 'abnormal' progress in each of the series, giving a basis for comparison of closure progress in each sex and stock with those of the male Whites, which were thereafter used as a standard (ibid.). They observed the following traits (Todd and Lyon 1924:333): 1) there was a clear orderly age sequence in the process of suture closure; 2) sex, racial stock, cephalic index and cranial capacity have very little effect on this closure sequence; and 3) the timing of the sequence was more obvious endocranially than ectocranially (ibid.).

In attempting to graph their results, Todd and Lyon (1924:334-335) decided not to arbitrarily subdivide age into units of one year. Instead, reasoning that each year of life includes, at the maximum, 18 months and successive ‘years’ overlap; the states of union for all individuals during three successive years of life was summed up, and the average taken in order to calculate a mean value for the state of union characteristic of the second of the three years.This ‘three year averaged’ age would became the focus of later criticism, since it apparently provided absolute ages at which a specific sutural phase would be exhibited. Their error was not including this averaged age in their tabulated results alongside the ‘arbitrary’ age ranges. For example, Todd and Lyon (1924:361) state that for white males, endocranial vault suture closure commences in the following order sagittal (22-23 years), coronal (24 years) and lambdoid (26 years), while closure is completed at 35, 41 and 47 years, respectively. Based upon these results, Todd and Lyon (1924:362) proposed that the rate of cranial suture closure was linked to the final stages of skeletal growth.

In order to test their findings, Todd and Lyon (1924:379) examined 30 randomly selected crania of known age. While, on average, their method provided close approximations of age at death, with a standard deviation of 6 years, it varied across individual crania (ibid.). Although, in comparison with later, revised methods of cranial suture estimation, Todd and Lyon did manage to produce estimated age ranges within 20 years of the actual age at death. However, Todd and Lyon (1924:380) state

our results are of distinct value however, when taken in conjunction with indications given by other parts of the skeleton.

In 1925, Todd and Lyon published three follow papers to the above study (Parts II-IV). Part II (Todd and Lyon 1925a) was an examination of ectocranial suture closure in adult males of white stock, since they acknowledged that in some instances, researchers would not be able to observe endocranial sutures. The sample consisted of the 267 crania employed in the first study, however, new samples were added for comparison as they became available during the course of these three studies (Todd and Lyon 1925a:24). This investigation concluded that (Todd and Lyon 1925a:36): 1) in general, there is no tendency on the part of sutures to begin to close earlier endocranially, rather than ectocranially; 2) the only exceptions to this finding were the pattern exhibited by the inferior masto-occipital, the spheno-frontal and the coronal; 3) ectocranial closure was slower and more variable, with no evidence of periodic activity; 4) ectocranial suture union was never as complete as endocranial closure; and 5) ectocranially, lapsed union is evident in all sutures.

In Part III (Todd and Lyon 1925b) of their research, Todd and Lyon focused upon endocranial suture closure in the ‘American negro’. They believed that this was an important area of study since they were attempting to ascertain whether or not their first study, of white males, could be employed as a standard for identifying age at death for different ‘racial stocks’ (Todd and Lyon 1925b:48). The initial sample consisted of 120 crania of known age from the Hamann collection. However, 41 crania were discarded for exhibiting abnormal traits, just as had been done in the two previous studies (Todd and Lyon 1925b:48). Todd and Lyon concluded that, allowing for individual variation amongst the negro crania, the endocranial closure pattern was generally the same as for the white sample (ibid.). However, they also conclude that Many negro skulls have been rejected as abnormal because of delay in closure of the lambdoid suture. It appears that some change is even now taking place in this region of the negro cranium which would indicate that they believe there is something different occurring within the ‘negro stock’, or, in more current terminology, there seems to be a population specific genetic variation in the endocranial closure of the lambdoid suture (Todd and Lyon 1925b:48).

In Part IV, Todd and Lyon (1925c) examined the occurrence of ectocranial suture closure in the male negro cranium. The sample consisted of the 79 crania selected for Part III of their study (Todd and Lyon 1925c:150). Their findings are as follows (Todd and Lyon 1925c:167-168): 1) endo and ectocranial suture closure patterns are essentially the same for white and negro males; 2) ectocranial closure is more erratic, slower and less complete than endocranial closure; and 3) lapsed union is characteristic of all ectocranial sutures, although it does not appear in all individuals.

In summary, Todd and Lyon (1924, 1925a, 1925b, 1925c) found the following age sequence for cranial suture morphology:

Suture	Endocranial			Ectocranial
	Open	Partial	Closed	Open	Partial	Closed
Sagittal	<23	20-37	>34	<24	23-30	>29
Coronal	<25	23-38	>36	<26	23-84	>26
Lambdoidal	<26	24-43	>41	<26	25-84	>30

These age ranges were applicable for both white and negro males (no racial differences in suture closure), and were a few years younger for females of both racial groups. When this methodology was tested on a random sample of 30 crania of known age, the standard deviation from the ‘real’ age at death was +/- 6 years.

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).

Bolk

In 1915, Louis Bolk calculated the absolute frequency of premature obliteration in 1820 European juvenile skulls, from which he (Bolk 1915:496) proposed the following terminology for suture closure: precocious (closure before the age of seven) and premature (closure after the age of seven but before the ‘normal’ age of closure).

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).

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.).