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The origin of snake feeding

机译：蛇食的起源

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Snakes are renowned for their ability to engulf extremely large prey, and their highly flexible skulls and extremely wide gape are among the most striking adaptations found in vertebrates. However, the evolutionary transition from the relatively inflexible lizard skull to the highly mobile snake skull remains poorly understood, as they appear to be fundamentally different and no obvious intermediate stages have been identified. Here we present evidence that mosasaurs—large, extinct marine lizards related to snakes—represent a crucial intermediate stage. Mosasaurs, uniquely among lizards, possessed long, snake-like palatal teeth for holding prey. Also, although they retained the rigid upper jaws typical of lizards, they possessed highly flexible lower jaws that were not only morphologically similar to those of snakes, but also functionally similar. The highly flexible lower jaw is thus inferred to have evolved before the highly flexible upper jaw—in the macrophagous common ancestor of mosasaurs and snakes—for accommodating large prey. The mobile upper jaw evolved later—in snakes—for dragging prey into the oesophagus. Snakes also have more rigid braincases than lizards, and the partially fused meso- and metakinetic joints of mosasaurs are transitional between the loose joints of lizards and the rigid joints of snakes. Thus, intermediate morphologies in snake skull evolution should perhaps be sought not in small burrowing lizards, as commonly assumed, but in large marine forms.
机译：蛇以吞噬极大型猎物的能力而闻名，其高度灵活的头骨和极宽的缝隙是脊椎动物中最引人注目的变种。然而，从相对不灵活的蜥蜴头骨到高度活动的蛇形头骨的进化过渡仍然知之甚少，因为它们似乎根本不同，并且没有发现明显的中间阶段。在这里，我们提供证据表明，mosasaurs是与蛇有关的大型灭绝的海洋蜥蜴，它代表着关键的中间阶段。蜥蜴是蜥蜴中唯一的一种，它具有长长的蛇状pa齿，可用来捕食猎物。同样，尽管它们保留了蜥蜴特有的刚性上颌骨，但它们具有高度灵活的下颌骨，不仅在形态上与蛇相似，而且在功能上也相似。因此，可以推断出高度灵活的下颚要先于高度灵活的上颚（在食龙和蛇的巨噬共同祖先）中进化，以容纳大型猎物。活动上颚后来演变成蛇形，以将猎物拖入食道。蛇也比蜥蜴具有更坚硬的脑壳，而蜥蜴的部分融合的中速和代谢动力学关节在蜥蜴的松散关节和蛇的刚性关节之间过渡。因此，也许不应该像通常假设的那样在小型洞穴蜥蜴中寻找蛇头骨进化中的中间形态，而应在大型海洋形式中寻找。

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