Rieppel O, Zaher H
Department of Geology, The Field Museum, Chicago, Illinois 60606-2496, USA.
J Morphol. 2001 Sep;249(3):252-66. doi: 10.1002/jmor.1053.
The skull of Acrochordus has been characterized by the absence of a crista circumfenestralis (a synapomorphy shared by all snakes), and by the absence of a recessus scalae tympani that in other squamates forms by subdivision of the embryonic metotic fissure. These traits have variably been identified as either plesiomorphic or paedomorphic. The study of the development of the osteocranium in a series of cleared and stained embryos of Acrochordus shows a close correspondence to the development of the skull in other snakes. The exception is the formation of the postorbital from two ossification centers. The significance of this observation, which might suggest the embryonic fusion of a postfrontal with a postorbital, remains enigmatic, as it is based on one side only of the skull of a single specimen. By contrast, a rudimentary and modified crista circumfenestralis can be identified in the skull of Acrochordus. Furthermore, absence of a recessus scalae tympani is not due to an undivided fissura metotica, but results from the obliteration of the anterior part of the metotic fissure instead. With respect to this character, Acrochordus is neither plesiomorphic, nor paedomorphic, but autapomorphic. This interpretation of the skull of Acrochordus is compatible with the sister-group relationships this genus shares with colubroid snakes.
没有眶周嵴（这是所有蛇类共有的一个近裔共性），并且没有鼓阶隐窝，而在其他有鳞类动物中，鼓阶隐窝是由胚胎期的颞骨裂细分形成的。这些特征被不同地认定为要么是祖征，要么是幼态持续特征。对一系列经过透明和染色处理的钝尾蛇胚胎的骨颅发育研究表明，其与其他蛇类头骨的发育密切对应。唯一的例外是眶后骨由两个骨化中心形成。这一观察结果的意义可能暗示额后骨与眶后骨在胚胎期融合，但由于它仅基于单个标本头骨的一侧，其意义仍然成谜。相比之下，在钝尾蛇的头骨中可以识别出一个退化且经过改变的眶周嵴。此外,鼓阶隐窝的缺失并非由于颞骨裂未分开，而是由于颞骨裂前部的闭塞所致。就这一特征而言，钝尾蛇既不是祖征，也不是幼态持续特征，而是自近裔特征。对钝尾蛇头骨的这种解释与该属与游蛇科蛇类的姐妹群关系相符。
