The bioarchaeology of a Japanese population from the Nozoji-ato site in Kamakura City, Japan

Abstract

The Japanese medieval period encompassed almost 400 years, between 1185 and 1573 AD. Previous research of human skeletal remains from medieval Kamakura City has shown that medieval people had a poor level of health and general living conditions because of malnutrition and interpersonal violence. The aims of this study are to apply bioarchaelogical analyses to a new series of human skeletal remains from the Nozoji-ato site in Kamakura City and to test the hypothesis that the bioarchaeological features that characterize medieval Japanese people are commonly seen in the new skeletal series. The Nozoji-ato site has been dated to a chronological age of between 1500 and 1700 AD based on the known sequence of coins and vessels, but most of these artefacts belonged to the medieval period. A sample size of 45 individuals was used in this study from individual graves. The results of this study indicate that the sample from Nozoji-ato is characterized by an old age-at-death distribution and high number of caries-lesion and ante-mortem tooth loss frequencies. Individuals from the Nozoji-ato site also tend to lack evidence for lethal trauma, a phenomenon that is frequently observed in other comparative medieval populations. The results presented in this study led to the conclusion that the Nozoji-ato exhibit different bioarchaeological features compared to the populations from the first half of the medieval period and that living conditions at this site were less severe than expected.

Introduction

The Japanese medieval period encompassed nearly 400 years, between 1185 and 1573 AD. This time period was characterized by the rise of the warrior class to political power and the establishment of a series of military governments or shogunates. In early work, Suzuki et al. (1956) were the first to conduct a systematic study of medieval Japanese human skeletons from the Zaimokuza burial site within Kamakura City, the center of a medieval period military government (Figure 1). The majority of the injuries in Zaimokuza skulls were scratches (82.3%), while only 2.7% were gashes (Suzuki et al., 1956). Many skull measurements from these individuals also evidenced dolichocephaly, chameprosopy, and prognathism, thought likely to be the result of environmental factors, including dietary conditions and the effects of medical care (Suzuki et al., 1956). These characteristics are noteworthy because the medieval Kamakura people are thought to be the most likely ancestors of modern Japanese (e.g. Dodo and Ishida, 1990, 1992; Hanihara, 1991).

Figure 1

Map of Kamakura City (Japan) showing the locations of archaeological sites: 1, Nozoji-ato; 2, Yuigahama Chusei Shudan Bochi (No. 372); 3, Zaimokuza; 4, Seiyokan; 5, Yuigahama-minami; 6, Yuigahama Chusei Shudan Bochi (Seika-ichiba).

Subsequent excavations at the Seiyokan, Yuigahama Chusei Shudan Bochi, and Yuigahama-minami sites, adjacent to Zaimokuza, have revealed that the medieval people in this region possessed a number of specific morphological features commonly found excavated burial sites, including dolichocephaly, chameprosopy, and prognathism (Nagaoka et al., 2006b). Nakahashi and Nagai (1985) showed that these specific morphological features were generally observed in the medieval human skeletal remains from the Yoshimohama site in the northern Kyushu-Yamaguchi District. It can be assumed that the medieval populations in Kamakura City represented medieval Japanese, because the specific features of the medieval Japanese were commonly observed in all over Japan (Nakahashi and Nagai, 1985) and the number of skeletal remains from the areas other than Kamakura City is small.

The first author of this study (T.N.) and colleagues have further elucidated a number of the characteristics of medieval Japanese urban inhabitants, including short life expectancy (Nagaoka et al., 2006a, 2008, 2013) and short stature (Nagaoka et al., 2008), alongside a low prevalence of dental caries (Nagaoka et al., 2013), and the ubiquitous presence of violence (Hirata et al., 2004; Nagaoka et al., 2009, 2010, 2013). These lines of evidence have all been used to suggest that the medieval people who inhabited this region were in a poor state of health and had difficult lives because of malnutrition and interpersonal violence. However, little is known about the variability of the bioarchaeological features in this time period. The aims of this study are to apply bioarchaelogical analyses to a new series of human skeletal remains from the Nozoji-ato site dating to the latter half of the medieval period and the beginning of the Edo period within Kamakura City in order to confirm the reproducibility of results relating to age-at-death structure, stature, dental caries, ante-mortem tooth loss (AMTL), and violence. This research also tests the hypothesis that the bioarchaeological features that characterize medieval Japanese people are commonly seen at the new skeletal series.

This study focused on the bioarchaeology of Kamakura City from the medieval to the early modern Edo periods, because the region was the center of politics, economics, religion, and culture at that time and the human skeletal remains from there provide information on the influence of urban environments on health.

Materials and Methods

The Nozoji-ato site is located within Kamakura City, Japan. The excavation of human remains from this site was initially undertaken in 2006 by the Kamakura Board of Education and we undertook to perform diagnoses in 2017. The Nozoji-ato was an old temple site of Nozoji, which was established in 1194, dedicated to the soul of a warrior, Yoshiaki Miura, and was destroyed by fire in 1872. Miura and his descendants were buried in the temple, but there is no information on the relationship of the excavated human skeletons to the Miura family. Most of the human skeletons excavated from this site were found articulated, but dried clay adhering to bones unfortunately led to the post-excavation cracking of fragile regions because of the 10-year time interval between excavation and research. The Nozoji-ato site is located in the eastern region to the archaeological sites at Zaimokuza, Seiyokan, Yuigahama Chusei Shudan Bochi (i.e. locations No. 372 and Seika-ichiba), and Yuigahama-minami (Figure 1). The Nozoji-ato site has been dated to the chronological age between 1500 and 1700 AD based on the known sequence of coins and vessels: two individuals were buried with Kanei-tsuho coins definitely dated to the Edo period (between 1600 and 1700 AD), while most of the human remains (associated with Eiraku-tsuho coins and vessels) belonged to the medieval period (between 1500 and 1600 AD) (Tamagawa-bunkazai-kenkyusho, unpublished data). This site is therefore later than other adjacent sites within Kamakura City that have been dated to the period between 1200 and 1500 AD. The difference in chronological age allows us to use the site to detect secular trends in bioarchaeological traits within the medieval period.

The comparative data used in this study were extracted from literature that addresses age-at-death and sex compositions (Nagaoka and Hirata, 2008; Nagaoka et al., 2013), stature (Hiramoto, 1972; Wada and Motomura, 2000; Nagaoka et al., 2008, 2013), dental caries (Sakura, 1964; Fujita, 1995; Todaka et al., 2003), enamel hypoplasia (Sawada, 2010; Nagaoka et al., 2013), cribra orbitalia (Hirata, 1990), and violence (Suzuki et al., 1956; Hirata et al., 2004; Nagaoka et al., 2009, 2010, 2013) within samples. The chronological ages encompassed by comparative samples include the Jomon (between 14500 and 300 BC), Yayoi (between 300 BC and 300 AD), Kofun (between 300 and 800 AD), medieval (between 1185 and 1573 AD), and Edo (between 1603 and 1867 AD) periods. The medieval sites of Zaimokuza, Seiyokan, Yuigahama Chusei Shudan Bochi (i.e. locations No. 372 and Seika-ichiba), and Yuigahama-minami known within Kamakura City all belong to the earlier half of this period, while the Marunouchi (or Muromachi) site within the Tokyo metropolis belongs to the second half. The sites of Hitotsubashi, Joshinji, and Unkoin within Tokyo have all been dated to Edo period sites. The Yuigahama Chusei Shudan Bochi site at Seika-ichiba is abbreviated as ‘Yuigahama Chusei Shudan Bochi.’

The age-at-death estimates for non-adult skeletons (14 years and less) used in this study were based on the diaphyseal lengths of limb bones (Scheuer et al., 1980), the completeness of crowns and roots (Ubelaker, 1989), the degree of development and closure of the occipital synchondrosis (Wakebe, 1990), and the degree of ossification and epiphyseal union of the pelvis and long bones (Brothwell, 1981). In contrast, the chronological metamorphosis of the auricular surface of the ilium (Buckberry and Chamberlain, 2002) and the pubic symphysis (Brooks and Suchey, 1990; Sakaue, 2006), as well as dental wear (Lovejoy, 1985) were utilized in the case of adult individuals 15 years of age and older. As the auricular surface of the ilium is resistant to decay in both forensic and archaeological contexts and appears to capture a wide range of ages throughout life (Storey, 2007), it is a reliable indicator (Kobayashi, 1967; Lovejoy et al., 1985; Buckberry and Chamberlain, 2002; Osborne et al., 2004; Igarashi et al., 2005). The young and elderly categories used in this study approximately corresponded with stages 1–3 and stages 4–7, respectively, based on the correlation between age and Buckberry and Chamberlain’s stage in the Japanese reference collection (Nagaoka et al., 2012). Age categories were divided into young and elderly based on a cutoff point of 35 years of age, and the stages of the Buckberry–Chamberlain system that describe the chronological metamorphosis of the ilium auricular surface were used to compare adult age-at-death structure between populations.

Sex determination of individuals 15 years of age and older was performed via a macroscopic assessment of pelvic (i.e. preauricular sulcus, greater sciatic notch, composite arch, inferior pelvis, ischiopubic proportions, ventral arc, subpubic concavity, and the medial aspect of the ischiopubic ramus) (Phenice, 1969; Bruzek, 2002) and cranial features (i.e. nuchal crest, mastoid process, orbital margin, glabella, and mental eminence) (Walker, 2008).

Stature was estimated in this study using the equations outlined by Fujii (1960) and Sasou and Hanihara (1998) that utilize the maximum lengths of the humerus, radius, femur, and tibia. These equations are useful because they lead to only small discrepancies in estimated stature based on each of these four different long bones from medieval Japanese specimens (Nagaoka et al., 2008). Maximum length measurements of these bones were taken following the method proposed by Martin and Knussmann (1988). The estimated stature based on Fujii’s equations was used for inter-population comparison, because Fujii’s equations were used to calculate the estimated stature in the comparative samples (Hiramoto, 1972; Wada and Motomura, 2000).

Caries lesion observations were made by eye and with dental instruments. All teeth were grouped as either anterior, premolar, or molar following the method outlined by Oyamada et al. (2007). Enamel color changes lacking depressions were excluded, however, because these are difficult to identify as caries lesions, and frequencies were calculated for tooth units (i.e. the number of affected teeth was divided by the total number of teeth observed) (Lukacs, 1995).

Counts of AMTL were performed by eye on the basis of complete dental socket absorption; AMTL percentages were calculated by dividing the number of AMTLs by the sum of the number of teeth and AMTLs.

Enamel hypoplasia frequencies were examined to clarify physical condition during both infancy and childhood; thus, following the method of Hillson (1996), deficiencies in enamel thickness (e.g. horizontal furrows and pits on surfaces) were identified as examples of this condition. The presence, or absence, of hypoplasia in the upper central incisors and lower canines that retained more than half the crown were recorded, with each tooth observed macroscopically using a LED light (Panasonic BF-425).

The existence of cribra orbitalia in individuals was diagnosed via observations of the exposure of trabecular bone within expanded cancellous bone (Hirata, 1990; Aufderheide and Rodríguez-Martín, 1998).

The location, type, and mechanism of traumas, as well as their healing processes, were considered in this study (Waldron, 2009).

Fisher’s exact test and the Student’s t-test were used for analyses in the software package R 3.1.2 (R Core Team, 2014).

The presence of caries lesions and AMTL were identified by T.N. and the second author of this study (K.H.), while limb bone maximum length measurements were performed by K.H. All other observations and analyses were performed by T.N.

Results

Age-at-death and sex compositions

As discussed above, 45 individuals were included in this analysis, of whom 8 were non-adult, and 37 were adult skeletons (Figure 2). The sample sex ratio of 4 males and 31 females indicates a sexually biased skeletal population (Figure 2); 17.8% of the sample from Nozoji-ato had died before 15 years of age and the ratio of 8 non-adults to 37 adults was 0.21 (Table 1). The proportion of non-adult deaths at Nozoji-ato (i.e. 17.8%; 8/45) is significantly less than that recorded at Hitotsubashi (i.e. 52.2%; 108/207) (P < 0.01), and is not significantly different from data for Yuigahama Chusei Shudan Bochi (i.e. 23.3%, 7/30) (P > 0.05).

Figure 2

The age-at-death and sex composition of the human skeletal remains from the Nozoji-ato site.

Table 1 Comparison of the proportion of deaths between the Nozoji-ato site and samples from other sites

Comparison of the proportion of non-adults and adults
Population	Period	Locality	Number of individuals		Proportion of individuals		Fisher’s exact test
			Non-adults	Adults	Non-adults	Adults
Nozoji-ato	Medieval to Edo	Kamakura	8	37	0.178	0.822
Yuigahama Chusei Shudan Bochi1	Medieval	Kamakura	7	23	0.233	0.767	P = 0.377
Hitotsubashi2	Edo	Tokyo	108	99	0.522	0.478	P = 0.000**

Comparison of the proportion of young and elderly adults
Population	Period	Locality	Number of individuals		Proportion of individuals		Fisher’s exact test
			Young adults	Elderly adults	Young adults	Elderly adults
Nozoji-ato	Medieval to Edo	Kamakura	8	21	0.276	0.724
Yuigahama Chusei Shudan Bochi1	Medieval	Kamakura	6	9	0.400	0.600	P = 0.501
Hitotsubashi2	Edo	Tokyo	25	74	0.253	0.747	P = 0.812

1  Nagaoka et al. (2013);

2  Nagaoka and Hirata (2007, 2008).

**  P < 0.01.

The percentages classified into young and elderly groups are 27.6% (8/29) and 72.4% (21/29), respectively, in Nozojiato (Table 1). Although data from the Nozoji-ato and Hitotsubashi sites showed 12.4–14.7% higher proportions of elderly individuals than Yuigahama Chusei Shudan Bochi, there is no significant difference in proportions between present-day and comparative samples (P > 0.05) (Figure 3; Table 1).

Figure 3

Comparison of age-at-death composition between the Nozoji-ato population and samples from other sites.

Stature

The data in Table 2 shows the maximum length of limb bones and estimates for stature based on the equations presented by Fujii and Sasou-Hanihara. Due to the small sample size, the inter-population comparison was conducted on females alone. The estimated stature of skeletons from Nozoji-ato was 148.5 cm (females) using Fujii’s equations for the maximum length of the right femur (Table 3). The stature of female skeletons from Nozoji-ato is not significantly different from that reported at Yuigahama Chusei Shudan Bochi, Yuigahama-minami, Muromachi, Yayoi, and Kofun (P > 0.05), but are significantly higher than those from Zaimokuza (P < 0.05) and Edo (P < 0.05) (Figure 4; Table 3).

Table 2 Estimated stature from maximum length of limb bones

		Humerus	Humerus	Radius	Radius	Femur	Femur	Tibia	Tibia
		Maximum length	Maximum length	Maximum length	Maximum length	Maximum length	Maximum length	Maximum length	Maximum length
		Right	Left	Right	Left	Right	Left	Right	Left
Male	Number of individuals	2	2	1	1	2	2	1	1
	Mean (cm)	289.5	284.0	231.0	227.8	406.0	406.5	323.0	318.4
Female	Number of individuals	10	9	10	8	13	11	10	12
	Mean (cm)	276.8	275.3	211.4	208.4	390.6	392.5	316.7	311.1
	Standard deviation (cm)	12.5	12.7	10.2	7.8	11.6	11.1	13.3	15.5
Estimation using Fujii’s equations
Male	Number of individuals	2	2	1	1	2	2	1	1
	Mean (cm)	154.0	153.3	158.9	158.6	155.2	155.2	153.8	152.7
Estimation using Fujii’s equations
Female	Number of individuals	11	9	10	8	13	11	10	12
	Mean (cm)	147.7	147.3	149.1	148.8	148.5	149.3	147.5	146.6
	Standard deviation (cm)	3.4	3.2	3.2	2.5	2.6	2.6	2.9	3.6
Estimation using Sasou and Hanihara’s equations
Female	Number of individuals	11	9	10	8	13	11	10	12
	Mean (cm)	145.9	145.3	148.0	147.3	146.3	146.7	146.3	145.2
	Standard deviation (cm)	3.1	3.6	3.3	2.7	2.5	2.3	3.2	3.9

Table 3 Comparison of estimated stature between the Nozoji-ato site and samples from other sites

Population	Period	Locality	Male			Female			Student’s t-test
			Number of individuals	Mean (cm)	Standard deviation (cm)	Number of individuals	Mean (cm)	Standard deviation (cm)
Nozoji-ato	Medieval to Edo	Kamakura	2	155.2		13	148.5	2.6
Zaimokuza1	Medieval	Kamakura	17	159.0	4.3	5	144.9	3.3	P = 0.026*
Yuigahama Chusei Shudan Bochi2	Medieval	Kamakura	5	158.7	6.8	4	146.3	3.6	P = 0.195
Yuigahama-minami3	Medieval	Kamakura	36	157.8	4.6	31	147.3	4.3	P = 0.356
Muromachi1	Medieval	Tokyo	26	156.8	4.7	17	146.6	3.8	P = 0.134
Jomon1	Jomon	Kanto	11	159.1	4.2	9	148.1	3.0	P = 0.742
Yayoi4	Yayoi	Northern Kyushu and Yamaguchi	77	161.4	4.5	66	150.8	4.0	P = 0.051
Kofun1	Kofun	Kanto	22	163.1	5.5	9	151.5	4.8	P = 0.072
Edo1	Edo	Tokyo	95	157.1	4.5	45	145.6	3.9	P = 0.015*

Stature is esimated from Fujii’s (1960) equations using the maximum length of femur.

1  Hiramoto (1972);

2  Nagaoka et al. (2013);

3  Nagaoka et al. (2008);

4  Wada and Motomura (2000).

*  P < 0.05.

Figure 4

Comparison of estimated stature between the Nozoji-ato population and samples from other sites. * P < 0.05.

Dental caries and AMTL

The data presented in Table 4 illustrates recorded frequencies of caries and AMTL at Nozoji-ato. Results reveal caries frequencies of 16.4% (29/177) in the upper jaw, 9.4% (16/171) in the lower jaw, and 12.9% (45/348) in both jaws. Elderly females also exhibited significantly higher caries lesion frequencies in the upper anterior teeth (P < 0.05), lower total teeth (P < 0.05), and upper and lower total teeth (P < 0.01) than younger females (Figure 5a; Table 4).

Table 4 Frequency of dental caries and antemortem tooth loss (AMTL)

Sex	Age		Upper				Lower				Total
			Anterior	Premolar	Molar	Total	Anterior	Premolar	Molar	Total
Male	Total adults	Number of teeth	5	4	4	13	6	5	3	14	27
		Number of carious teeth	0	0	0	0	0	0	0	0	0
		Number of AMTL	0	0	0	0	0	1	4	5	5
		Caries frequency	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000
		AMTL frequency	0.000	0.000	0.000	0.000	0.000	0.167	0.571	0.263	0.156
Female	Young adults	Number of teeth	44	35	28	107	40	31	23	94	201
		Number of carious teeth	2	5	5	12	1	1	3	5	17
		Number of AMTL	0	0	5	5	1	3	10	14	19
		Caries frequency	0.045	0.143	0.179	0.112	0.025	0.032	0.130	0.053	0.085
		AMTL frequency	0.000	0.000	0.152	0.045	0.024	0.088	0.303	0.130	0.086
Female	Elderly adults	Number of teeth	19	15	14	48	27	20	16	63	111
		Number of carious teeth	5	4	2	11	2	3	6	11	22
		Number of AMTL	9	8	5	22	9	4	8	21	43
		Caries frequency	0.263	0.267	0.143	0.229	0.074	0.150	0.375	0.175	0.198
		AMTL frequency	0.321	0.348	0.263	0.314	0.250	0.167	0.333	0.250	0.279
Female	Unknown adults	Number of teeth	3	4	2	9					9
		Number of carious teeth	3	2	1	6					6
		Number of AMTL	4	1	3	8					8
		Caries frequency	1.000	0.500	0.500	0.667					0.667
		AMTL frequency	0.571	0.200	0.600	0.471					0.471
Female	Total adults	Number of teeth	66	54	44	164	67	51	39	157	321
		Number of carious teeth	10	11	8	29	3	4	9	16	45
		Number of AMTL	13	9	13	35	10	7	18	35	70
		Caries frequency	0.152	0.204	0.182	0.177	0.045	0.078	0.231	0.102	0.140
		AMTL frequency	0.165	0.143	0.228	0.176	0.130	0.121	0.316	0.182	0.179
Male + Female	Total adults	Number of teeth	71	58	48	177	73	56	42	171	348
		Number of carious teeth	10	11	8	29	3	4	9	16	45
		Number of AMTL	13	9	13	35	10	8	22	40	75
		Caries frequency	0.141	0.190	0.167	0.164	0.041	0.071	0.214	0.094	0.129
		AMTL frequency	0.155	0.134	0.213	0.165	0.120	0.125	0.344	0.190	0.177
Fisher’s exact test between young and elderly females
		Caries	P = 0.022*	P = 0.247	P = 0.668	P = 0.085	P = 0.560	P = 0.287	P = 0.123	P = 0.017*	P = 0.007**
		AMTL	P = 0.000**	P = 0.000**	P = 0.467	P = 0.000**	P = 0.004**	P = 0.221	P = 1.000	P = 0.039*	P = 0.000**

*  P < 0.05;

**  P < 0.01.

Figure 5

Comparison of (a) dental caries occurrence and (b) AMTL between young and elderly age categories. * P < 0.05; ** P < 0.01.

The AMTL frequencies recorded in this study were 16.5% (35/212) in the upper jaw, 19.0% (40/211) in the lower jaw, and 17.7% (75/423) in both jaws. Data show that these frequencies were significantly higher in elderly females compared to their younger counterparts in the upper anterior, premolar, and total dental samples (P < 0.01), as well as in the lower anterior (P < 0.01) and total (P < 0.05), and upper and lower total dental (P < 0.01) samples (Figure 5b; Table 4).

Data also reveal that individuals at the Nozoji-ato site exhibited a significantly higher frequency of caries lesions (i.e. 12.9%; 45/348) than the medieval period populations from Zaimokuza (i.e. 5.5%; 147/2669) (P < 0.01), Yuigahama Chusei Shudan Bochi (i.e. 5.1%; 24/475) (P < 0.01), and Yuigahama-minami (i.e. 9.5%; 261/2755) (P < 0.05), as well as samples from the Jomon Period (i.e. 8.2%; 271/3295). Recorded frequencies from Nozoji-ato are, however, lower than those seen in the Yayoi (i.e. 19.4%; 354/1823) (P < 0.01), Joshinji (i.e. 20.4%; 108/530) (P < 0.01), and Unkoin (i.e. 19.3%; 123/638) (P < 0.05) samples (Figure 6a; Table 5). Similarly, the AMTL frequency at Nozoji-ato (i.e. 17.7%; 75/423) is significantly higher than values recorded at either Yuigahama Chusei Shudan Bochi (i.e. 6.5%; 36/550) (P < 0.01) or Yuigahama-minami (i.e. 3.8%; 134/3531) (P < 0.01), also dated to within the medieval period (Figure 6b; Table 5).

Figure 6

Comparison of (a) dental caries occurrence and (b) AMTL between Nozoji-ato and samples from other sites. * P < 0.05; ** P < 0.01.

Table 5 Comparison of frequency of dental caries and antemortem tooth loss (AMTL) between the Nozoji-ato site and samples from other sites

Population	Period	Locality	Number of teeth	Number of carious teeth	Frequency	Fisher’s exact test
Nozoji-ato	Medieval to Edo	Kamakura	348	45	0.129
Zaimokuza1	Medieval	Kamakura	2669	147	0.055	P = 0.000**
Yuigahama Chusei Shudan Bochi2	Medieval	Kamakura	475	24	0.051	P = 0.000**
Yuigahama-minami3	Medieval	Kamakura	2755	261	0.095	P = 0.045*
Marunouchi1	Medieval	Tokyo	548	80	0.146	P = 0.553
Jomon4	Jomon	All Japan	3295	271	0.082	P = 0.005**
Yayoi5	Yayoi	Northern Kyushu-Yamaguchi	1823	354	0.194	P = 0.004**
Joshinji1	Edo	Tokyo	530	108	0.204	P = 0.005**
Unkoin1	Edo	Tokyo	638	123	0.193	P = 0.013*

Population	Period	Locality	Number of teeth	Number of AMTL	Frequency	Fisher’s exact test
Nozoji-ato	Medieval to Edo	Kamakura	423	75	0.151
Yuigahama Chusei Shudan Bochi2	Medieval	Kamakura	550	36	0.061	P = 0.000**
Yuigahama-minami3	Medieval	Kamakura	3531	134	0.037	P = 0.000**

1  Sakura (1964);

2  Nagaoka et al. (2013);

3  Oyamada et al. (2007);

4  Fujita (1995);

5  Todaka et al. (2003).

*  P < 0.05;

**  P < 0.01.

Enamel hypoplasia and cribra orbitalia

The recorded frequencies of enamel hypoplasia at the Nozoji-ato site were 58.5% (24/41) in the upper central incisor and 85.7% (24/28) in the lower canine (Table 6). Data show that the frequency of hypoplasia in the upper central incisor at Nozoji-ato was significantly lower than that seen during the Jomon period (i.e. 77.6%; 114/147) (P < 0.05), while no significant differences were seen in the lower canine between the data from this site and comparative samples (P > 0.05) (Table 6).

Table 6 Comparison of frequency of linear enamel hypoplasia and cribra orbitalia between the Nozoji-ato site and samples from other sites

Linear enamel hypoplasia
Population	Period	Locality	Sex	Upper central incisor			Fisher’s exact test	Lower canine			Fisher’s exact test
				Number of teeth	Number of teeth affected	Hypoplasia frequency		Number of teeth	Number of teeth affected	Hypoplasia frequency
Nozoji-ato	Medieval to Edo	Kamakura	Male	3	3	1.000		2	2	1.000
			Female	38	21	0.553		26	22	0.846
			Total	41	24	0.585		28	24	0.857
Yuigahama Chusei Shudan Bochi1	Medieval	Kamakura	Total	24	16	0.667	P = 0.602	15	11	0.733	P = 0.419
Jomon2	Jomon	All Japan	Total	147	114	0.776	P = 0.027*	169	156	0.923	P = 0.272
Yayoi2	Yayoi	Northern Kyushu-Yamaguchi	Total	157	106	0.675	P = 0.275	187	144	0.770	P = 0.338
Hitotsubashi2	Edo	Tokyo	Total	45	26	0.578	P = 1.000	55	46	0.836	P = 1.000

Cribra orbitalia
Population	Period	Locality	Sex	Number of orbits	Number of affected orbits	Cribra orbitalia frequency	Fisher’s exact test
Nozoji-ato	Medieval to Edo	Kamakura	Male	1	0	0.000
			Female	20	6	0.300
			Total	21	6	0.286
Seiyokan3	Medieval	Kamakura	Total	57	14	0.246	P = 0.773
Jomon3	Jomon	Kanto	Total	44	4	0.091	P = 0.065
Hitotsubashi3	Edo	Tokyo	Total	102	37	0.363	P = 0.619

¹  Nagaoka et al. (2013);

2  Sawada (2010);

3  Hirata (1990).

*  P < 0.05.

The presence of cribra orbitalia was detected in 6 out of 21 orbits (28.6%) when both sexes were combined and there was no significant difference in lesions between Nozoji-ato and comparative samples (P > 0.05) (Table 6).

Depressed fractures

The sample from the Nozoji-ato site studied in this paper includes the presence of two depressed fractures in a female aged between 15 and 34 years (specimen no. 47). Observations show that the fracture on the anterior of the right parietal comprises a depression that is 30 mm long, while its counterpart on the posterior right parietal is circular and 20 mm in length (Figure 7). These fractures are both shallow, limited to the outer table, and poorly aligned. The fact that these depressions have smooth edges and contain newly formed vascular foramina linked with new bone formation implies that they were formed ante-mortem and that this individual likely subsequently survived. In both cases, these features were identified as blunt-force fractures produced by the direct application of force onto the cranial vault. The frequency of the trauma is 2.2% (1/45).

Figure 7

Depressed fractures on the cranium of a young female from the Nozoji-ato site.

Discussion

Sample age-at-death and sex composition

The sex ratio composition reconstruction presented here reveals the presence of 4 males and 31 females within the sample. It is noteworthy, however, that as this determination was carried out based on the macroscopic assessment of pelvic bones with high reliability, misclassification cannot explain such a biased ratio. Yoshiaki Miura and his descendants were buried in the Nozoji temple and it cannot be ruled out that the high-status warriors and their family were included in the materials and the biased sexual ratio is related to unusual situations of death and mortuary practice. However, the reasons underlying this bias remain unclear.

Age-at-death comparisons among the populations studied in this research demonstrate that, in spite of the absence of significant differences, the Nozoji-ato sample appeared to be older at death on average than the individuals from Yuigahama Chusei Shudan Bochi. Indeed, the distribution of the Nozoji-ato sample more closely resembles that of the Edo period rather than the medieval period. In earlier work, Nagaoka et al. (2006a) demonstrated that life expectancy improved over the few hundred years between the medieval and Edo periods; the dated age of the Nozoji-ato site is thought to fall between the latter half of the medieval period and the beginning of the Edo period, later than other adjacent sites within Kamakura City. This means that differences in demographic profiles between populations within the area of medieval Kamakura City can be attributed to variations in chronological age within this period as life expectancy also increased over this time span.

Comparing the level of urban sanitation experienced by both medieval and Edo populations has also led to the suggestion that population concentration within Kamakura City at this time impacted negatively on the lives of inhabitants (Nagaoka et al., 2006a). Analyses of archaeological remains suggest that population densities within cities during the medieval period were higher than they are at present, and the bodies of horses and people were often abandoned in side ditches or on streets within Kamakura City (Kawano, 1989, 1995). In contrast, customs related to hygiene, food, and drink, and the more general absence of domestic animals that characterize the Edo period, suggest that living conditions at this time were actually more sanitary than in contemporary European cities (Hanley, 1997). It is generally the case that the period between the medieval and Edo periods corresponded to a time of improvements in urban living conditions; historical demographers have noted that dietary conditions as well as the nature of clothes, houses, bathing facilities, and urban sanitation all improved drastically within the Edo period and led to concomitant increases in life expectancy (Kito, 2000). The level of urban sanitation within Kamakura City during the latter half of the medieval period remains unknown, but it is reasonable to consider that the increasing life spans seen at this time were likely due to improvements in health.

Stature

The results of this study show that the average estimated stature of females living at the Nozoji-ato site was significantly larger than observed for Zaimokuza and Edo. This result is not consistent with previous studies, which have demonstrated that average estimated stature gradually decreased from the Yayoi period into the medieval period and on into the Edo period (Hiramoto, 1972; Nagaoka et al., 2008). Height differences between people at Nozoji-ato and Zaimokuza may also reflect improvements in their living circumstances even though results from the former are not significantly difference to data from other medieval sites.

Dental caries and AMTL

The data presented in this study show that the individuals living at Nozoji-ato had a significantly higher frequency of caries-lesions than the medieval populations at Zaimokuza, Yuigahama Chusei Shudan Bochi, and Yuigahama-minami, as well as Jomon period individuals. At the same time, however, the frequency of these lesions was significantly lower at this site than is seen during the Yayoi and Edo periods, while individuals from Nozoji-ato are also characterized by a significantly higher frequency of AMTL than seen at either Yugiahama Chusei Shudan Bochi or Yuigahama-minami. It has generally been accepted that variations in dental caries and the prevalence of AMTL can likely be explained by the changes in subsistence and diet. The development of agriculture around this time is known to have reduced oral health levels and increased the prevalence of dental caries (e.g. Lukacs, 1992; Larsen, 1997); it is also the case that the rate of caries prevalence was higher within Japanese Yayoi period agriculturists than in Jomon period hunter-gatherers (e.g. Oyamada et al., 1996; Todaka et al., 2003). Medieval period dietary habits seem unlikely to explain the prevalence of caries lesion at the Nozoji-ato site, however; archaeological remains from medieval Kamakura City indicate that people at this time utilized rice, nuts, millet, soybeans, fruit, meat, and fish, for example, and cooked these foods using kitchen knives, kettles, pans, and mortars (Kawano, 1995). Studies on the history of Japanese food also imply that the ingredients utilized by common people during the medieval period were almost the same as those seen in historic Japan (see Sakura, 1964).

One possible alternative explanation for the recorded caries and AMTL prevalence is the old age-at-death distribution and female-biased sex ratio at the Nozoji-ato site. Increases in both caries and AMTL rates from younger to older age categories might be explained by the elderly age composition at Nozoji-ato compared to Yuigahama Chusei Shudan Bochi. In addition, the female-biased sex ratio at this site may also influence the recorded caries prevalence; higher rates of this condition in females have been reported in both modern and ancient populations and have usually been explained by easier access to food during preparation, the earlier eruption of permanent teeth, and pregnancy (Lukacs and Largaespada, 2006). In bioarchaelogical settings, females also tend to exhibit higher rates of AMTL than males due to a higher intake of cariogenic foods and sexual division of labor (Larsen, 1997). The frequency of caries in both upper and lower teeth was also significantly higher in females (8.3%; 14/169) than in males (3.3%; 10/306) at the Yugiahama Chusei Shudan Bochi site, while there was no significant difference in the AMTL rate (males: 4.8%; 16/334; females: 9.7%; 20/216) in spite of a slightly higher rate in females (Nagaoka et al., 2013). Females from Nozoji-ato further exhibited a significantly higher AMTL frequency (17.9%; 70/391) than their Yugiahama Chusei Shudan Bochi counterparts (9.7%; 20/216) (P < 0.01), while there was no significant difference in caries frequency between the individuals from these two sites (Nozoji-ato: 14.0%; 45/321; Yugiahama Chusei Shudan Bochi: 8.3%; 14/169) (P > 0.05) in spite of a slightly higher rate in Nozoji-ato. Thus, an older age-at-death composition and female-biased sex ratio provides a plausible explanation for the high caries and AMTL prevalence at Nozoji-ato.

Enamel hypoplasia and cribra orbitalia

Enamel hypoplasia is defined as the presence of developmental defects in dental enamel induced by metabolic stress that result from nutritional disorders or diseases during the formation period of this material (e.g. Goodman and Rose, 1990; Hillson, 1996). In contrast, cribra orbitalia is a pathological change characterized by aggregations of small foramina in the orbital roof in response to marrow hyperplasia in spongy bone. It is generally accepted that the presence of cribra orbitalia indicates bone deformation caused by anemia due to iron deficiency (Hirata, 1990).

The frequencies of enamel hypoplasia and cribra orbitalia recorded in the Nozoji-ato population are almost equal to those seen in Edo period series. Sawada (2010) showed higher frequencies of enamel hypoplasia in the Jomon period than in the Edo period. On the other hands, previous studies in this area have suggested that Edo period people had the highest frequencies of enamel hypoplasia and cribra orbitalia among Japanese populations; this result has been used to provide evidence for the fact that these people lived under stressful conditions, including high population concentrations and the presence of infectious diseases (Yamamoto, 1988; Hirata, 1990). It is therefore safe to conclude, based on current data, that there was no difference in living conditions between the Nozoji-ato site and those seen during the Edo period.

Depressed fractures

The presence of a trauma on one female cranium from Nozoji-ato has also been demonstrated in this study. In this case, fractures were identified as likely due to a blunt force produced by direct application, a level of violence that is generally observed at all archaeological sites around Kamakura City, coincident with continuous conflicts and turbulence throughout this period (Suzuki et al., 1956; Morimoto, 1987; Morimoto and Hirata, 1992; Hirata et al., 2004; Nagaoka et al., 2009, 2010, 2013). The remains from Nozoji-ato are different, however, from those reported from Zaimokuza (Suzuki et al., 1956), Seiyokan (Nagaoka et al., 2010), Yuigahama Chusei Shudan Bochi (Nagaoka et al., 2009, 2013), and Yuigahama-minami (Hirata et al., 2004) because they do not exhibit lethal cranial cuts. In contrast, human skeletons from Seiyokan, Yuigahama Chusei Shudan Bochi, and Yuigahama-minami are not characterized by blunt-force traumas, while just one female from Zaimokuza has been identified with a lethal trauma due to blunt force (Suzuki et al., 1956). The absence of any evidence for healing in the Zaimokuza trauma case is also in contrast to the depressed fractures seen on skulls from Nozoji-ato.

Variation in bioarchaeological traits within Kamakura City

The results of this study demonstrate that the individuals who lived at the Nozoji-ato site were different from the populations within medieval Kamakura City. A few specific conclusions can be drawn, including that the Nozoji-ato sample is characterized by an older age-at-death distribution than specimens from Yuigahama Chusei Shudan Bochi (although this difference is not significant). The population at Nozoji-ato is characterized by a significantly higher rate of caries-lesion and AMTL frequencies than are seen at the Zaimokuza, Yuigahama Chusei Shudan Bochi, and Yuigahama-minami sites. Evidence for lethal trauma appears to be absent from the individuals at Nozoji-ato even though this has been frequently observed at the medieval sites within Kamakura City.

The results of this study suggest that the people living within Kamakura City from the medieval period to the beginning of the Edo period showed wider intra-population variations in health conditions than previously anticipated. These results, contrast with earlier findings that medieval populations are homogeneous in short life spans (Nagaoka et al., 2006a, 2013), and low rates of dental caries and AMTL (Sakura, 1964; Nagaoka et al., 2013). One important outstanding question is whether or not the findings reported here are consistent with the accepted theory that medieval people generally experienced poor health conditions and had relatively shorter life expectancy. Over the last ten years, one of the present authors (T.N.) and colleagues have conducted bioarchaeological studies on thousands of medieval human skeletons from known sites within Kamakura City, including Seiyokan, Yuigahama Chusei Shudan Bochi, and Yuigahama-minami. The presence of cut marks on crania from these sites strongly implies that violence was prevalent in Medieval Japan (Hirata et al., 2004; Nagaoka et al., 2009, 2010, 2013), while a paleopathological study of Yuigahama-minami individuals revealed the first evidence for leprosy and tuberculosis in this region at the time (Hirata et al., 2011), alongside less frequent degenerative spinal changes than seen in Okhotsk and Kumejima skeletal series (Shimoda et al., 2012). Paleodemographic studies have also demonstrated a higher proportion of young individual deaths at this time than is seen in the subsequent Edo period of Japan; this also implies that living conditions in medieval Kamakura City were harsh because of malnutrition and warfare (Nagaoka et al., 2006a, 2013; Nagaoka and Hirata, 2008). New data from the Nozoji-ato series dated to the chronological age between the latter half of the medieval period and the beginning of the Edo period has demonstrated secular trends within a few hundreds of years and it is therefore reasonable to conclude that the people at this time did not exhibit homogeneous pathological features and that living conditions at this site were less severe than during the first half of this time period.

Acknowledgments

The authors would like to express their gratitude to Dr. S. Mizushima and Mr. H. Seike of the St. Marianna University School of Medicine for their help. This study was partially supported by JSPS Kakenhi grant number 15K07241.

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