Science：化石暗示蛇来源于穴居动物？
发布人：管理员 浏览次数： 发布时间：2015-07-27
文字说明: 长有四条腿的蛇Tetrapodophis amplectus 制服了一个gondwanatherian 哺乳动物。这一场景处于冈瓦纳早白垩纪的热带森林中。
一个长有四条腿的蛇的化石的发现提示，这一动物亚目或是从穴居动物始祖而不是海从洋动物演化而来的。在巴西的克拉图组中发现的独特的四条腿的样本能让我们更多地了解这些生物如何转变成如今我们所熟悉且常常害怕的光洁、滑行的爬行动物。通过将之与其它已知蛇类物种进行比较来分析这一物种的基因学和形态学特征，并在4个不同分析中给予每个因子不同的权重，作者们确认该四条腿的动物实际上是现代蛇的始祖。新近发现的物种Tetrapodophis amplectus(它生活在1.46亿年至1亿年前的早白垩世)保留了许多典型的蛇类特征——例如：短吻、长颅、拉长的身体、长有鳞片、尖牙及一个可吞下大型猎物的活动下颌。它也保留着在现代蛇类中所见的典型的脊椎结构，它能赋予收束猎物所需的极端的灵活性。Tetrapodophis与蛇类的主要且明显的差异是它有4个肢体，这些肢体看来不像是用于移动身体。作者们说，相反，其较短的外指和加长的第二指表明，这些肢体是被用来抓握的，即用于抓住猎物或用于在交配时的紧抱。作者们还提出，该物种没有在海洋动物中常被发现的长长的、侧扁形尾巴，这进一步表明蛇类不是从海洋始祖演化而来的。因此，这一令人着迷的化石暗示了蛇类是如何最终滑行进入现代世界的。由Susan Evans撰写的一篇《视角》更为详细地对这一化石进行了讨
论。
原文链接：
A four-legged snake from the Early Cretaceous of Gondwana
原文摘要：
Snakes are a remarkably diverse and successful group today, but their evolutionary origins are obscure. The discovery of snakes with two legs has shed light on the transition from lizards to snakes, but no snake has been described with four limbs, and the ecology of early snakes is poorly known. We describe a four-limbed snake from the Early Cretaceous (Aptian) Crato Formation of Brazil. The snake has a serpentiform body plan with an elongate trunk, short tail, and large ventral scales suggesting characteristic serpentine locomotion, yet retains small prehensile limbs. Skull and body proportions as well as reduced neural spines indicate fossorial adaptation, suggesting that snakes evolved from burrowing rather than marine ancestors. Hooked teeth, an intramandibular joint, a flexible spine capable of constricting prey, and the presence of vertebrate remains in the guts indicate that this species preyed on vertebrates and that snakes made the transition to carnivory early in their history. The structure of the limbs suggests that they were adapted for grasping, either to seize prey or as claspers during mating. Together with a diverse fauna of basal snakes from the Cretaceous of South America, Africa, and India, this snake suggests that crown Serpentes originated in Gondwana.
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