## 3 Results and Discussion
### Isotopic Analysis in Modern Mammals
#### 3.2.2 \(\delta^{34}\)S Values of Various Mammals
The maximum difference between recent and old fish from the same specimen (Sparidae) is 0.5% for \(\delta^{13}\)C values and 3% for \(\delta^{15}\)N (not available data for \(\delta^{34}\)S), while for the Scombridae specimens, it is 3.3%, for \(\delta^{13}\)C values and 1.5% for \(\delta^{15}\)N. In general, there are more significant differences between ancient individuals from the same species, e.g., for sparidae (median \(\delta^{13}\)C = \(-12.6\%\), sd:3.7%) and Scombridae (median \(\delta^{13}\)C = \(-14.4\%\), sd:2.1%), than between recent individuals from different species (median \(\delta^{13}\)C = \(-16.3\%\), sd:2.3%). Furthermore, in freshwater fish species, there are differences between ancient (median \(\delta^{13}\)C = \(-19.2\%\), sd: 3.1%; \(\delta^{15}\)N = \(8.7\%\), sd:1.3%) and recent individuals (Cyprinidae) (median \(\delta^{13}\)C = \(-17.9\%\), sd:0.9%; \(\delta^{15}\)N = \(8.0\%\), sd: 3.0%). The differences between marine and freshwater fish species are either due to the diversity in the trophic structure of marine ecosystems, probably reflecting the natural changes in local environmental conditions or even due to modern human activities (e.g., fishing, overfishing, aquaculture, or contamination). All these aspects can be considered as potential factors affecting the great range of the obtained isotopic results, which in turn reflect the changes in trophic structures and feeding strategies and, particularly, the feeding strategies adopted by various fish species. The fish species living at low levels exhibit \(\delta^{13}\)C and \(\delta^{15}\)N values very close to those of terrestrial resources (see Figures 11 and 12), which means that it is difficult to detect them isotopically. This indicates that it is difficult to detect a fish consumption of less than 10% of the total diet by weight, and so, the isotopic values of human collagen would be closer to a C3 terrestrial diet. Furthermore, zooarchaeological data (see Table 5) have been incorporated into Figures 11 and 12. They concern stable sulfur isotope analysis from Greek remains: (a) the analysis of assemblages from the Bronze Age sites at Chamalevri (mammal samples, 13 Km from Rethymno) in Crete [48] and (b) the analysis of assemblages from Thessaly, central Greece, dating to the Early Iron Age [72] and the local archaeofauna (mainly ovicaprids) from the Classical site of Thebes (5 th c. BC) [73]. Animal \(\delta^{34}\)S values range from 2 to 18.2% [51; 72; 73]. The data from Crete and Thebes [52; 73] have shown that coastal sites, while having a terrestrial diet based on C-N isotopic values, show high \(\delta^{34}\)S values closer to marine values (\(\approx\)+20%) due to the sea spray effect. In contrast, the \(\delta^{34}\)S values of the mammals from Thessaly (Voulokaliva and Kephalosi coastal sites) have not been influenced by the \"sea-spray\" like in the case studies of Crete and Thebes [51; 73]. At the same time, a comparison between recent and ancient mammals demonstrates that both groups drop in the same range. Nevertheless, minor isotopic differences among them might be attributed to intensive exploitation and the systematic cultivation of fausal (different fodder) and flora (cereals and legumes). On the other hand, there are major \(\delta^{34}\)S differences (Table 5) among ancient and recent herbivore individuals rather than between recent mammals of different species. The low standard deviation (SD: 1.47%; see Table 5) of recent herbivores mammals reflects a homogenous sulfur isotope data set. This could be attributed to the regional differences caused by the complex structural geology of Greece (see Figure 7) and therefore is depicted in sulfur isotopes. The larger isotope sulfur differences between ancient and recent cattle from Crete Island are probably caused by the diversity in the trophic structure of terrestrial ecosystems and may reflect the natural changes in local environmental conditions or modern human activities.