Abstract
The Mersin Chal cemetery lies to the east of Telajim village, situated in the Poshtkouh district of Mehdi Shahr city. This site is located in the north of Semnan province, within Iran’s central plateau. The Telajim region offers significant biological diversity and livelihood potentials, providing the Mersin Chal people access to a diverse range of flora and fauna. Studying the skeletal remains from the Mersin Chal cemetery serves as an important resource for understanding various aspects, including paleodiet, dietary habits, and human behaviors. They provide insights into the levels of adaptation and environmental compatibility, and offer a basis for modeling economic conditions. The focus of this research was to investigate the biological and subsistence strategies employed by the individuals buried in this cemetery during the second half of the first millennium BC, utilizing bioarchaeological methods. To achieve the stated objective, a key question emerges: how can the dietary patterns of the population from the study area be identified through stable isotope analysis conducted on biological samples obtained from archaeological excavations at the Mersin Cal cemetery? To address the question, this study employs a laboratory-analytical approach, specifically stable carbon (δ13C) and nitrogen (δ15N) isotope analysis, conducted on dental collagen samples. Statistical methods were applied to analyze and interpret the results from the isotope analysis. The investigation focuses on the human skeletal remains from 12 graves among 49 excavated burials at the Mersin Cal cemetery. Physical anthropological research indicates that the examined skeletal remains are of adults, encompassing both male and female individuals. Considering the biological potentials of the studied area, this research concluded that the Mersin Chal community had a mixed diet based on C3 and C4 plants. Their protein intake was derived predominantly from herbivores (a diet based on C3 and C4 plants), with a smaller portion coming from carnivores.
Keywords: Mersin Chal Cemetery, The Second Half of the First Millennium BC, Biological Strategies, Dental Collagen, Carbon Isotope, Nitrogen Isotope.

Introduction
“Human skeletal remains serve as the foundation for shaping both individual and collective experiences of the world throughout our lifetime. The dual nature of skeletal remains, viewed both as biological and cultural entities, serves as a basis for theoretical research in bioarchaeology, which studies the biological remains left by past peoples in their cultural contexts (ancient sites)” (Afshar, 2018:82). Chemical analysis of bones and teeth has become a fundamental tool in bioarchaeology, offering insights into human migration and movement, livelihoods, biological strategies, paleodiet, gender differences, etc (Basu et al., 2015; Bogaard & Outram, 2013:333, Lewis et al., 2017:45, Makarewicz & Sealy, 2015:146-14). The isotopic composition of a diet can be assessed by analyzing the ratio of carbon (δ13C) and nitrogen (δ15N) isotopes found in the collagen of bones and teeth (Agarwal & Glencross, 2011: 413-414). The isotopic values (δ13C and δ15N) derived from the food consumed by animals and humans are incorporated into their tissues. By analyzing the stable isotopes of carbon and nitrogen in the dental collagen of human remains, it is possible to determine the proteins consumed by each individual in the last years of their life due to tissue regeneration processes (Bocherens et al., 2005:10; Budd et al., 2013:862). Therefore, it is essential to identify the main components of the diet, including C3 and C4 plants, marine-based proteins, and non-protein sources (Price, 2015: 74). The stable carbon isotope ratio (δ13C) serves as an indicator for estimating the proportional intake of C3 and C4 plants in both human and animal diets. C3 plants have more negative δ13C values (-20 to -35%), and C4 plants have more positive δ13C values (-9 to -14%) in human skeletal collagen (Agarwal and Glencross, 2011:414, Ambrose, 1986:711, Ambrose and Lynette, 1993:2-3, Price, 2015:73, Katzenberg, 2008:423-424). The proportion of the stable carbon isotope is influenced by dietary intake, whereas the proportion of the stable nitrogen isotope is affected by both diet and habitat conditions (Katzenberg, 2008: 430-431). Nitrogen isotope (δ15N) levels are influenced not only by trophic level but also by environmental variables like rainfall and agricultural management practices, including fertilization methods (Budd et al., 2017:5; Sołtysiak, 2020:117; Sołtysiak and Schutkowski, 2018:1). In this regard, this research focuses on reconstructing the livelihood patterns and biological strategies of the people buried in the Mersin Chal cemetery during the second half of the first millennium BC, utilizing an analysis of the stable isotopes δ13C and δ15N.

Discussion 
Analyzing carbon and nitrogen isotopes in skeletal remains, including bones and teeth, provides valuable insights into palaeodiet, biological strategies, and dietary habits. The isotope values (δ¹³C and δ¹⁵N) found in the food consumed by animals and humans are retained within the tissues of the individual consumer. By analyzing stable carbon and nitrogen isotopes found in the dental/bone collagen of human or animal remains, it is possible to identify the diet consumed during the last years of the individual’s life (Bocherens et al., 2005: 10; Budd et al., 2013: 862). In the third season of archaeological excavations at the Mersin Chal cemetery in 2021, 49 pit grave burials dating back to the second half of the first millennium BC were identified (Nemati, 2021). Skeletal remains, much like other archaeological evidence, have significant value in reconstructing the past. This research examined the remains obtained from this cemetery using a bioarchaeological approach. A total of 12 skeletal remains with third molars were chosen for laboratory isotopic analysis.  The samples consisted entirely of adult skeletons, comprising a mix of both male and female individuals. Carbon and nitrogen isotope analyses were conducted at the Center for Physical Science and Technology in Vilnius, Lithuania, utilizing an isotope ratio mass spectrometer. These analyses revealed that the δ¹³C ratios varied between -16.33% and -17.86%, while δ¹⁵N ranged from 11.12% to 8.61%. These isotopic values indicate a mixed diet based on C3 and C4 plants, as well as protein sources such as herbivores and carnivores. Sołtysiak & Schutkowski (2018) noted, “The isotopic values of domesticated ungulates (goats, sheep, and camels) overlap with humans. However, certain instances reveal slightly more positive δ¹³C values. Conversely, wild ungulates (gazelles and horses) show higher δ¹³C values and lower δ¹⁵N values compared to humans and domesticated animals. The presence of more positive δ¹³C values in wild ungulates suggests that these ungulates (gazelles, equines) occasionally grazed on C4 plants” (Sołtysiak & Schutkowski, 2018: 7). The δ¹³C isotope values provide insight into dietary habits: higher positive values suggest a likelihood of consuming C4 plants, while lower negative values point to the consumption of C3 plants. It highlights that the primary source of fodder for the herbivores contributing to their diet came from both C3 and C4 plants. The geographical position of Mersin Chal cemetery, situated in a region rich in environmental assets and diverse flora and fauna, has granted the community convenient access to food resources.

Conclusion 
The carbon and nitrogen isotope analysis of skeletal remains from the Mersin Chal cemetery holds significant value as a key aspect of archaeological research, offering crucial insights and serving as a vital source of information for reconstructing past cultures and studying the social and economic conditions of past societies. Research on paleo-nutrition has predominantly centered on the examination of skeletal remains. Collagen found in biological remains, such as teeth and bones, serves as the foundation for carbon and nitrogen isotopic analysis. Consequently, ensuring the presence of collagen in optimal condition is one of the most important criteria for selecting a skeleton for isotopic research. If the amount of collagen in the sample is insufficient, the sample becomes unsuitable for analysis. Thus, to reliably reconstruct dietary patterns, it is crucial to use samples with intact and well-preserved collagen. The tooth samples from the Mersin Chal skeletal remains exhibit favorable collagen quality indicators, including collagen concentration, collagen yield ranging between 16.12% and 7.67%, carbon concentration between 40.16% and 36.38%, nitrogen concentration from 14.60% to 13.28%, and a C/N atomic ratio spanning 3.25 to 3.18, confirming their well-preserved condition. Analysis of stable carbon (δ13C) and nitrogen (δ15N) isotopes in the dental collagen extracted from skeletal remains at the Mersin Chal cemetery revealed that the isotopic values for the region fall within the ranges of δ13C (-16.33% to -17.86%) and δ15N (11.12% to 8.61%). These isotopic values indicate a diet composed of C3 plants, including cultivated cereals such as wheat and barley, as well as rice, legumes, vegetables, and fruits, and also C4 plants. The people of this region primarily derived their protein from herbivores that fed on C3 plants, such as goats, sheep, and camels, as well as from herbivores with a mixed diet of C3 and C4 plants, including cattle, gazelles, and equines. Based on isotopic evidence, the inhabitants of this region incorporated carnivores such as Felidae indet into their diet, albeit in limited amounts. carbon and nitrogen isotope analyses have revealed no evidence of aquatic-based dietary contributions, indicating that the Mersin Chal community relied entirely on terrestrial animals as their primary protein source. Considering the rich biological diversity of the research field, it is clear that the Mersin Chal community has direct access to both plant and animal food resources. These environmental potentials have played a crucial role in shaping the most suitable biological strategies for the residents of this region.