Vipera walser is the most recently recognized European viper. This rare species is endemic to a small area in the Piedmont Alps of Italy, but its closest relatives are found among the Caucasian viper species. In order to provide a starting point for a phylogenetic and biogeographic investigation based on osteology, and including fossils remains, we analyzed four specimens of V. walser and compared them with specimens of the four other Italian viper species. Based on these specimens, we improved the diagnosis of V. walser and provided a first evaluation of intraspecific variability and ontogenetic variation. The skull of V. walser is subject to significant variation, most likely related to ontogeny in some cases (i.e., development of the parietal crest, development of the basioccipital process, shape of the posterior margin of the parabasisphenoid, shape of the quadrate). Based on the studied material, it is possible to distinguish V. walser from the other Italian vipers by the shape of the occipital crest of the supraoccipital, which is posteriorly directed, whereas it is laterally directed in the other species. The osteological diagnosibility provides further support for the validity of V. walser as a distinct species from Vipera berus.

中文翻译：

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Vipera walser (Squamata, Viperidae) 的头骨骨学：与其他意大利毒蛇相比的描述、变异性、个体发育和诊断特征

Vipera walser 是最近被认可的欧洲毒蛇。这种稀有物种是意大利山麓阿尔卑斯山的一个小地区特有的，但在高加索毒蛇物种中发现了它的近亲。为了为基于骨学的系统发育和生物地理学调查提供一个起点，包括化石遗骸，我们分析了 V. walser 的四个标本，并将它们与其他四个意大利毒蛇物种的标本进行了比较。基于这些标本，我们改进了 V. walser 的诊断，并对种内变异和个体遗传变异进行了初步评估。V. walser 的颅骨有显着的变异，在某些情况下最有可能与个体发育有关（即顶骨嵴的发育、基底枕突的发育、副副蝶骨后缘的形状、正方形的形状）。根据所研究的材料，可以通过枕骨上枕嵴的形状将 V. walser 与其他意大利毒蛇区分开来，该形状是向后定向的，而在其他物种中则是横向定向。骨学可诊断性进一步支持 V. walser 作为与 Vipera berus 不同的物种的有效性。