Apesteguía Sebastián, Zaher Hussam
Museo Argentino de Ciencias Naturales Bernardino Rivadavia, A. Gallardo 470, Buenos Aires (1405), Argentina.
Nature. 2006 Apr 20;440(7087):1037-40. doi: 10.1038/nature04413.
It has commonly been thought that snakes underwent progressive loss of their limbs by gradual diminution of their use. However, recent developmental and palaeontological discoveries suggest a more complex scenario of limb reduction, still poorly documented in the fossil record. Here we report a fossil snake with a sacrum supporting a pelvic girdle and robust, functional legs outside the ribcage. The new fossil, from the Upper Cretaceous period of Patagonia, fills an important gap in the evolutionary progression towards limblessness because other known fossil snakes with developed hindlimbs, the marine Haasiophis, Pachyrhachis and Eupodophis, lack a sacral region. Phylogenetic analysis shows that the new fossil is the most primitive (basal) snake known and that all other limbed fossil snakes are closer to the more advanced macrostomatan snakes, a group including boas, pythons and colubroids. The new fossil retains several features associated with a subterranean or surface dwelling life that are also present in primitive extant snake lineages, supporting the hypothesis of a terrestrial rather than marine origin of snakes.
人们普遍认为，蛇通过逐渐减少肢体的使用而逐渐失去了四肢。然而，最近的发育学和古生物学发现表明，肢体退化的情况更为复杂，而化石记录中对此的记载仍然很少。在此，我们报告一种化石蛇，其骶骨支撑着骨盆带，并且在胸腔外有强健、可发挥功能的腿部。这块来自巴塔哥尼亚上白垩统时期的新化石填补了向无肢进化过程中的一个重要空白，因为其他已知的具有发育良好后肢的化石蛇，如海洋中的哈氏蛇、厚蛇和真足蛇，都没有骶骨区域。系统发育分析表明，这块新化石是已知最原始（基部）的蛇，所有其他有肢化石蛇都更接近更高级的巨口蛇类，该类群包括蟒、蚺和游蛇科。这块新化石保留了一些与地下或地表栖息生活相关的特征，这些特征在现存原始蛇类谱系中也存在，这支持了蛇起源于陆地而非海洋的假说。
