Revisions in the microscopic method of estimating age at death in human cortical bone.

Problems recently discovered in the Kerley method of estimating age at death from cortical microstructure are discussed. Kerley's original data have been re-analyzed to produce new regression equations and to document the original field size.     

Histologic estimation of age at death using the anterior cortex of the femur

This report describes a new histologic method for determination of age at death, the latest in a series of studies that began with Kerley's pioneer presentation in 1965. The study population was collected from 328 documented individuals from an anatomy dissecting room in the United States, from two modern cemeteries in the Dominican Republic, and from autopsies performed in a Chilean hospital. Undecalcified thin sections 1.0 cm wide were made from specimens taken from the femoral midshaft directly opposite the linea aspera. Five 0.886 mm2 fields were located at the periosteal edge and photographed, mainly for purposes of defining the fields and providing a permanent record. Secondary osteons, type II osteons, osteon fragments, resorption spaces, and non-Haversian canals were recorded as number/mm2, and a 100-space grid was used to measure average percent of unremodeled, osteonal, and fragmental bone. Stepwise regression analysis of the measurements produced a series of regression equations for age estimation for females, males, and sexes combined. Most equations have a standard error of estimate of about 10 years, but the coefficients of determination (r2) range from 0.48 to 0.72. In practice, sex-specific equations gave better results than opposite-sex or nonspecific equations, mainly because males and females differed in the pattern of relations between osteons and osteon fragments with advancing age.     

Practising methods of age determination. Comments on methods combining multiple age indicators

For some time, trends in age determination of skeletons have tended to shift from methods using single age indicators to methods combining multiple age indicators. Evidently the latter are expected to offer more balanced age assessments. If one decides to apply a method using multiple age indicators, a choice can be made between two «current» methods, both based on non-metrical age indicators: the socalled Complex Method of Acsádi and Nemeskéri, statistically elaborated by Sjøvold (WEA, 1980), and the so-called Multifactorial Method of Lovejoy et al., 1985a. Comments are given on practical applicability and supposed confidence.     

Skeletal age determination based on the os pubis: A comparison of the Acsádi-Nemeskéri and Suchey-Brooks methods

After reviewing various systems of age determination based on analysis of the pubic bone, the discussion concentrates on the collection and preparation of an extensive autopsy sample (n=1225) of pubic bones from modern individuals with legal documentation of age at death (death and/or birth certificates). TheSuchey-Brooks method derived from this sample is described. TheAcsádi-Nemeskéri system is evaluated in terms of the documented collection and it is seen that their five stage method focuses only on the early and late morphological changes. The intermediate stages, in which the ventral rampart is in process of completion, are not described. Their suggested age ranges do not correspond with the documented modern sample. Based on these limitations of theAcsádi-Nemeskéri method, applications of theSuchey-Brooks system are discussed.     

Comparison of two histological techniques for age determination in small cetaceans

Age estimation in odontocetes is based on counts of growth layer groups (GLGs) deposited in recording structures such as teeth. Generally, tooth sections are obtained using a cryostat microtome. However, some researchers prefer obtaining thin sections using a traditional paraffin microtome. Little information is available on the application of this technique to dolphin teeth. Our main aim was to investigate if the paraffin technique can be a viable alternative. We considered whether estimated age would be affected by preparation technique, staining method, and section thickness, while controlling for effects of species, body length, and sex. We also analyzed whether the staining method would affect readability of GLGs and age reading variability. Teeth from 86 individuals (representing seven species) were used, but not all were prepared using both techniques because sufficient teeth were not available in all cases. Although the staining method had significant effects on the estimated age using both techniques, the variability of GLG counts was small and appeared to be similar for both techniques. Using Mayer's hematoxylin stained sections of 8 μm thickness, good agreement of ages was obtained from both techniques, with more preparations classified as "good quality" for the paraffin technique. Mayer's hematoxylin provided the best contrast of the GLGs when using the paraffin technique. We conclude that the paraffin technique is viable and represents a cost-effective alternative to a cryostat microtome when preparing cetacean teeth for age determination.     

The staining of fish otoliths for age determination

Attempts were made to find methods for the staining of fish otoliths which would give results comparable to those of the Christensen burning technique. A variety of different histological stains and otoliths of different species were experimented with. Otoliths of sole, turbot, brill and scad gave best results when sectioned and stained in acidified Neutral Red, whereas those of cod, hake, whiting, plaice and grey mullet showed up the annuli better when dyed in aqueous Aniline Blue or Toluidine Blue and then sectioned. Small, translucent otoliths such as those of pelagic species may be enhanced by staining in Eosin Y.     

Effects of field size when using Kerley's histological method for determination of age at death

The field size at which a bone is read affects the results obtained when using Kerley's histological method for age estimation, even after applying the recommended correction factor. Whereas there is no tendency for any one of three field sizes tested to consistently underestimate or overestimate age, a field size closest to that used by Kerley in his original study had significantly lower variances for its age estimates, and thus provides greater reliability. This particular field size yields more precise estimates because it is sampling a pattern and number of structures more similar to that of Kerley. Correction factors cannot equalize the counts of osteons and osteon fragments because of spatial variations in the distributions of these histological structures. A field size similar to that used by Kerley in gathering the data from which he developed his regression equations must be used to assure that the same pattern and number of structures is being sampled. For this reason, we suggest a field size as close to 2.06 mm² as possible be used when employing Kerley's method.     

Accuracy, precision and quality control in age determination, including a review of the use and abuse of age validation methods

Many calcified structures produce periodic growth increments useful for age determination at the annual or daily scale. However, age determination is invariably accompanied by various sources of error, some of which can have a serious effect on age-structured calculations. This review highlights the best available methods for insuring ageing accuracy and quantifying ageing precision, whether in support of large-scale production ageing or a small-scale research project. Included in this review is a critical overview of methods used to initiate and pursue an accurate and controlled ageing program, including (but not limited to) validation of an ageing method. The distinction between validation of absolute age and increment periodicity is emphasized, as is the importance of determining the age of first increment formation. Based on an analysis of 372 papers reporting age validation since 1983, considerable progress has been made in age validation efforts in recent years. Nevertheless, several of the age validation methods which have been used routinely are of dubious value, particularly marginal increment analysis. The two major measures of precision, average percent error and coefficient of variation, are shown to be functionally equivalent, and a conversion factor relating the two is presented. Through use of quality control monitoring, ageing errors are readily detected and quantified; reference collections are the key to both quality control and reduction of costs. Although some level of random ageing error is unavoidable, such error can often be corrected after the fact using statistical ('digital sharpening)' methods.     

Interobserver error in macroscopic methods of estimating age at death from the human skeleton

This research evaluates the interobserver error when the macroscopic methods recommended by American and European anthropologists to estimate age at death of a skeleton, were applied to a sample of the Terry Collection (Smithsonian Institution, Washington D.C.). Although no statistical differences among observers were found for any of these methods, small dissimilarities suggest that techniques using a narrower scale of categories produce greater agreement among researchers. The present study is within a wider research project designed to evaluate the accuracy of these methods, when applied to an identified (age known) sample of 963 skeleton from the Terry Collection.     

Field age determination of leopards by tooth wear

Age determination is an important tool in wildlife studies. Estimating the age of animals in the field using tooth wear criteria may be subject to error as a result of variations between individuals, habitats and populations. Data on age estimation of leopards and tooth wear characteristics are lacking. Nineteen leopards in Namibia were assessed for tooth eruption and wear. Between 1991 and 1995 leopards (including 13 individuals of known age) were monitored at one year intervals ('28 leopard years') to record age and tooth wear. At the age of two years leopards had fully developed dentition. Wear started with the incisors and canines, and spread to the premolars and molars. A chronology of tooth eruption and wear in relation to age is presented. Above the age of three years, male leopards showed higher frequencies of enamel flaking and canine fractures than females.     

Pteridine fluorescence for age determination of Anopheles mosquitoes

The age structure of mosquito populations is of great relevance to understanding the dynamics of disease transmission and in monitoring the success of control operations. Unfortunately, the ovarian dissection methods currently available for determining the age of adult mosquitoes are technically difficult, slow and may be of limited value, because the proportion of diagnostic ovarioles in the ovary declines with age. By means of reversed-phase HPLC this study investigated the malaria vectors Anopheles gambiae and An. stephensi to see if changes in fluorescent pteridine pigments, which have been used in other insects to determine the age of field-caught individuals, may be useful for age determination in mosquitoes. Whole body fluorescence was inversely proportional to age (P < 0.001, r2 > 91%) up to 30 days postemergence, with the regression values: y = 40580-706x for An. gambiae, and y = 52896-681x for An. stephensi. In both species the main pteridines were 6-biopterin, pterin-6-carboxylic acid and an unidentified fluorescent compound. An. gambiae had only 50-70% as much fluorescence as An. stephensi, and fluorescent compounds were relatively more concentrated in the head than in the thorax (ratios 1:0.8 An. gambiae; 1:0.5 An. stephensi). The results of this laboratory study are encouraging. It seems feasible that this simpler and faster technique of fluorescence quantification could yield results of equivalent accuracy to the interpretation of ovarian dissection. A double-blind field trial comparing the accuracy of this technique to marked, released and recaptured mosquitoes is required to test the usefulness of the pteridine method in the field.     

An evaluation of two biochemical methods of age determination in insects (pteridines and lipofuscins) using the ant Polyrhachis sexpinosa Latrielle (Hymenoptera: Formicidae)

Accurate information on the age of wild-caught animals is valuable for a variety of areas, but can be particularly difficult to obtain for small holometabolous insects, whose body size is fixed at the time of pupal eclosion. A variety of chemical groups, such as lipofuscins and pteridines accumulate in body tissues through time and can be used to predict age in a variety of arthropod taxa. Here we use spectrofluorometry to confirm the presence of extractable levels of lipofuscins and pteridines in individual social insects (using the ant Polyrhachis sexpinosa Latrielle, average body size 25 mg, as an example) and evaluate their ability to predict age. Pteridine levels were independent of age but lipofuscin levels increased with age in a predictable manner ( r ² = 72.8%). Lipofuscin levels therefore represent a new method of age determination for social insects that should be applicable to both individual laboratory and wild-caught animals.     

Determination of age at death in human skeletal remains: A comparison of two techniques

Reliable palaeodemographic reconstruction is dependent upon accurate determination of age at death in human skeletal remains. Two methods, Todd (Todd, 1920, 1921) and Suchey-Brooks (Katz & Suchey, 1986), which use morphological changes of theos pubis as an indicator of age at death, were applied to a sample of Central California Indians. Life tables were constructed and the two data sets were compared. Differences between the two data sets were evident when life expectancies, mean ages, and survivorship curves were compared. Because both methods were developed using male samples, only the male data were considered valid. In a comparison between the two male data sets it became apparent that the differences lie in the upper decades depending upon which method was used. In an attempt to rectify the difference in age ranges between the two methods, a conversion of Todd phases into equivalent Suchey-Brooks phases (Katz & Suchey, 1986) was employed. Applications and limitations of both methods are discussed and it is suggested that the Suchey-Brooks method is to be perferred.     

Comparison of a Bone Criterion and a dental Criterion for estimation of age at death in the study of an Ancient Cemetery

Two methods, a visual method based on the appearance of the auricular surface of the ilium and a metric method based on two dental criteria, were used in conjunction for estimation of skeletal age at death in paleodemographic study of an ancient cemetery, and were found to be coherent. However, the paleodemographic profiles differed according to sex, indicating a sexual difference in the evolution of the sacroiliac joint.     

Percent osteonal bone versus osteon counts: the variable of choice for estimating age at death.

Ahlqvist and Damsten's (1969) modification of the Kerley (1965) method for histological age estimation uses percent osteonal bone, rather than actual osteon counts, in order to eliminate the difficulty of distinguishing between intact and fragmentary osteons. Since their method has been developed for the femur only, and several more recent methods have been proposed that utilize percent osteonal bone, a study was undertaken to ascertain the relative value of percent osteonal bone compared with osteon counts to estimate age at death for the radius, tibia, and fibula. First the question of how much of the cross-section of a bone should be sampled was addressed by comparing the results of regression against age for percent osteonal bone derived from sampling only four fields with those derived from the entire cross-section of the radius. A significant age association was found only when the entire cross-section was sampled. In order to evaluate the relative merit of using either percent osteonal bone, or osteon counts to estimate age, each variable was regressed against age. Significant correlation coefficients were found for all three bones when the independent variable was osteon counts. When percent osteonal bone was employed, a significant correlation was found only for the radius. Stepwise linear regression found osteon counts for the fibula alone to be the best age predictor. Finally, a repeated measures analysis of variance revealed that percent osteonal bone and osteon counts both differ among the three bones within an individual. Based upon these results, osteon counts, rather than percent osteonal bone, should be the variable of choice when developing histological age predicting methods.     

Multifactorial determination of skeletal age at death: a method and blind tests of its accuracy

Traditional methods of estimating skeletal age at death have relied solely on the pubic symphyseal face or on this indicator combined with others in nonsystematic ways. A multifactorial method is presented that uses a principal components weighting of five indicators (public symphyseal face, auricular surface, radiographs of proximal femur, dental wear, and suture closure). This method has been tested by completely blind assessment of age in two samples from the Todd collection carefully screened for accuracy of stated age at death. Results show a marked superiority of the multifactorial method over any single indicator with respect to both bias and accuracy. This represents the first truly blind test of an age-at-death indicator or system, as the test populations were independent of the system(s) being tested, and the age, sex, and ethnogeographic origin of the individuals being assessed (as well as the compositions of the test samples with respect to these variables) were completely unknown until the tests were completed. Implications for paleodemography are discussed.     

A comparison of staining techniques to improve precision of age estimation from fish otoliths

A total of 30 pairs of sagitta otoliths of horse mackerel Trachurus trachurus were sampled from three length-classes, and five staining methods were applied to each pair. Ten age estimates were obtained per fish, method and length-class. Significant differences in age estimates were found between methods, due to the variable enhancement in the otolith pattern produced by each method. A method using amido-schwartz as the staining reagent produced the best results in terms of precision of the age estimates.     

长鞭红景天主轴生长特性与年龄判定

长鞭红景天是国家第二批确定的二级保护植物,处于近危状态。在西藏色季拉山区不同海拔带设置样地,观测长鞭红景天花茎环的形成过程,用游标卡尺(IP54型)测量长鞭红景天植株不同年的轴向生长量和径生长量;分析其主轴生长特性,进行年龄判定,结果表明:长鞭红景天每年在主轴上形成一个花茎环结构,并且轴向生长量和径生长量在年际间均无显著差异,但随海拔升高,轴向生长量和径生长量均呈下降趋势。根据长鞭红景天主轴的生长特性,结合主轴的长度则可以判定其年龄,为进一步研究长鞭红景天种群结构及动态奠定基础。     

Evaluation of copper, iron and lead substitution techniques in elasmobranch age determination

Copper and lead substitution reactions were found to be useful in demonstrating growth patterns in vertebrae from several elasmobranch species. In contrast, iron substitution was ineffective in detecting variations in vertebral mineralization. The present study provides two alternative methods for elasmobranch age determination that may prove useful when traditional methods are deemed ineffective. However, species-specific variations in the efficiency of these methods reemphasize the observation that different types of vertebrae often require different methods of staining.