International Journal of Molecular Zoology, 2025, Vol.15, No.2, 78-89 http://animalscipublisher.com/index.php/ijmz 80 Water snakes and sea snakes are quite different in their evolution. Snakes that live in freshwater and semi-water can often be seen in rivers and wetlands. True sea snakes (including those of the Hydrophilidae family) mainly live in the warm shallow seas of the Indo-Pacific region. Where they live is largely influenced by temperature, the salt content in seawater and the number of Marine organisms. To adapt to different environments, their physical characteristics are also different. For instance, the body of a water snake is usually streamlined, while a sea snake has glands specifically designed to excrete salt. These differences can reveal the species variations of snakes in different environments and also indicate that they have evolved very successfully (Udyawer, 2015; Patron-Rivero et al., 2024; Hudry and Herrel, 2025). 3 Historical Climatic Driving Factors 3.1 Paleoclimate change During the Paleocene to Miocene periods, climate change played a significant role in the origin and early spread of snakes. After the Cretaceous-Paleogene (K-Pg) mass extinction, the global temperature dropped and was accompanied by intense environmental changes, which promoted the increase in the number of crown snakes, especially the spread and population establishment of some major branches such as African snakes to Asia. At this stage, snakes, especially sea snakes, exhibit higher specialization in morphology because they have adapted to the new living conditions brought about by climate change and continental drift (Klein et al., 2021; Jiang 2024). The climate change throughout the entire Cenozoic period, including the stages of warming and cooling, further affected the rate at which the number of snake species increased. For instance, in fossil snake families (such as the European Snake family), the rate at which the number of snake species increases is closely related to past temperature changes: when climate change is intense, the rate of species replacement is faster; By the late Miocene, the forest area had shrunk and become scattered, and the number of snake species had decreased. These findings demonstrate that snake populations are highly sensitive to long-term environmental changes and also illustrate the significance of past climates in shaping the current diversity of snakes (Cyriac and Kodandaramaiah, 2017). 3.2 Glacial and interglacial cycles The glacial and interglacial cycles of the Pleistocene had a significant impact on the distribution of snakes, especially in temperate regions. When glaciers move forward, the distribution range of snakes will shrink, and in some places, snakes may even become extinct. During interglacial periods, snakes can migrate to other places again and spread to new environments suitable for survival. Such cycles make snake populations fragmented and increase their genetic differences. This situation is more obvious in species with weak diffusion ability (Sahlean et al., 2014). The different preferences for temperature within the same species also affect their choice of whether to diffuse-individuals will adjust their movement patterns to adapt to the most suitable temperature for themselves, which not only helps them adapt to the local environment but also enables them to live separately in space as the climate gradient changes (Bestion et al., 2015). In tropical regions, glacial cycles have formed "sanctuaries" - areas with stable climates, where the species of snakes have remained at a relatively high level. These shelters are not only places for storing genetic diversity but also the central areas where snakes spread after the ice age. During the most intense glacial activity, tropical regions still had an environment suitable for snakes to survive, allowing many snake species to survive. Afterwards, these snakes migrated back to the surrounding areas to live, which has led to the presence of many species of snakes in these regions now (Cyriac and Kodandaramaiah, 2017; Klein et al., 2021). 3.3 Continental drift, sea level fluctuations and ocean circulation Land drift and subsequent changes in land position have a significant impact on the migration and geographical isolation of snakes. After the splitting of supercontinents, newly formed land Bridges or newly created geographical barriers promoted the spread and differentiation of snakes, shaping their distribution worldwide. For example, after the mass extinction of K-Pg, the formation time in the Caribbean region was relatively late. In
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