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.