Scanferla Agustín
CONICET , Instituto de Bio y Geociencias del NOA (IBIGEO) , 9 de Julio N° 14 (A4405BBB), Rosario de Lerma, Salta , Argentina.
R Soc Open Sci. 2016 Nov 9;3(11):160612. doi: 10.1098/rsos.160612. eCollection 2016 Nov.
Macrostomy is the anatomical feature present in macrostomatan snakes that permits the ingestion of entire prey with high cross-sectional area. It depends on several anatomical traits in the skeleton and soft tissues, of which the elongation of gnathic complex and backward rotation of the quadrate represent crucial skeletal requirements. Here, the relevance of postnatal development of these skull structures and their relationship with macrohabitat and diet are explored. Contrary to the condition present in lizards and basal snakes that occupy underground macrohabitats, elements of the gnathic complex of most macrostomatan snakes that exploit surface macrohabitats display conspicuous elongation during postnatal growth, relative to the rest of the skull, as well as further backward rotation of the quadrate bone. Remarkably, several clades of small cryptozoic macrostomatans reverse these postnatal transformations and return to a diet based on prey with low cross-sectional area such as annelids, insects or elongated vertebrates, thus resembling the condition present in underground basal snakes. Dietary ontogenetic shift observed in most macrostomatan snakes is directly linked with this ontogenetic trajectory, indicating that this shift is acquired progressively as the gnathic complex elongates and the quadrate rotates backward during postnatal ontogeny. The numerous independent events of reversion in the gnathic complex and prey type choice observed in underground macrostomatans and the presence of skeletal requirements for macrostomy in extinct non-macrostomatan species reinforce the possibility that basal snakes represent underground survivors of clades that had the skeletal requirements for macrostomy. Taken together, the data presented here suggest that macrostomy has been shaped during multiple episodes of occupation of underground and surface macrohabitats throughout the evolution of snakes.
巨口是巨口亚目蛇类所具有的解剖学特征，它使得蛇能够吞食具有较大横截面积的整个猎物。这一特征取决于骨骼和软组织中的若干解剖学特征，其中颌复合体的伸长和方骨的向后旋转是关键的骨骼要求。在此，我们探讨了这些头骨结构的出生后发育及其与宏观栖息地和饮食的关系。与占据地下宏观栖息地的蜥蜴和基干蛇类的情况相反，大多数利用地表宏观栖息地的巨口亚目蛇类的颌复合体元素在出生后生长过程中相对于头骨的其他部分表现出明显的伸长，同时方骨进一步向后旋转。值得注意的是，一些小型穴居巨口亚目蛇类的分支会逆转这些出生后的变化，回归到以具有低横截面积的猎物为食，如环节动物、昆虫或细长的脊椎动物，从而类似于地下基干蛇类的情况。在大多数巨口亚目蛇类中观察到的饮食个体发育转变与这种个体发育轨迹直接相关，表明这种转变是随着颌复合体在出生后个体发育过程中伸长和方骨向后旋转而逐渐获得的。在地下巨口亚目蛇类中观察到的颌复合体和猎物类型选择的众多独立逆转事件，以及已灭绝的非巨口亚目物种中对巨口的骨骼要求的存在，强化了基干蛇类代表具有巨口骨骼要求的类群的地下幸存者的可能性。综上所述，此处呈现的数据表明，在蛇类的整个进化过程中，巨口是在多次占据地下和地表宏观栖息地的过程中形成的。
