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Snake paleontology of the Siwalik group (Miocene of Pakistan): Correlation of a rich fossil record to environmental histories.

机译：Siwalik小组（巴基斯坦中新世）的蛇古生物学：丰富的化石记录与环境历史的关联。

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The fossil snake record of the Siwalik Group (Miocene), Pakistan, was examined to determine responses in diversity, ecology, and phyletic history to known environmental change. The Siwalik Group includes a rich fossil record of snake vertebrae spanning a temporal interval of 18–6 Ma, as well as known histories of environmental change including increasing aridity and seasonality and a transition from C3- to C4-dominated floras.; In order to determine the systematic utility of vertebral morphology in diagnosing Siwalik Group snakes, phylogenetic analysis was performed using a data matrix of 39 characters for 45 extant taxa. Analysis of established higher-order snake clades resulted in consensus hypotheses that are generally consistent with results based on alternative data sets. Species-level analysis found little or no support for some higher-order clades and most generic and specific relationships, due to a lack of lower-order synapomorphies.; Applying this analysis to the Siwalik Group snake record resulted in the recognition 13 taxa and morphotypes throughout the section, with an increase in raw taxonomic richness through time that is partially related to increasing sample sizes. However, comparisons of sample size to taphonomic factors do not demonstrate any significant relationship, except for a positive correlation to depositional environment for the record of Acrochordus dehmi, which may reflect habitat preferences of a fully aquatic taxon as opposed to differences in fluvial transport.; Taxonomic richness and equality indices demonstrate an increase between 10.0 and 9.0 Ma. Ecologically, this represents a transition from Acrochordus-dominated faunas to more diverse, balanced faunas including multiple terrestrial and semi-aquatic taxa. This transition is generally concurrent with increases in aridity and seasonality of precipitation inferred to represent the inception of the Asian monsoon system, and may represent a response to increases in environmental heterogeneity. Changing diversity between 8.0 and 6.5 Ma may be related to the C3–C4 floral transition, but more precise relationship is difficult to discern.; Examination of the Acrochordus dehmi fossil record does not corroborate previous hypotheses of phyletic change through time within the lineage. Estimated body lengths based on regression relationships between vertebral length and snout-vent length determined for extant taxa are 1.5 to 4.0 meters indicating that A. dehmi was larger than all living Acrochordus, with a consistent mean body length throughout its fossil record. Morphometric analysis of vertebral shape change through time does not reveal a pattern consistent with hypotheses of phyletic evolution or faunal turnover, but demonstrates that A. dehmi is morphometrically distinct from extant Acrochordus. Homogeneity in A. dehmi may have resulted from a low-energy physiology shared with extant Acrochordus, which could have served as a buffer against environmental change.
机译：检查了巴基斯坦Siwalik集团（中新世）的化石蛇记录，以确定其对已知环境变化的多样性，生态学和系统历史的响应。锡瓦里克（Siwalik）组拥有丰富的化石记录，记录了时间间隔为18-6 Ma的蛇脊椎，以及已知的环境变化历史，包括干旱和季节性增加以及从C3到C4为主的菌群过渡。为了确定椎体形态学在诊断Siwalik群蛇中的系统实用性，使用39个字符的数据矩阵对45个现存的类群进行了系统发育分析。对已建立的高阶蛇进化枝的分析得出的共识假设通常与基于替代数据集的结果一致。物种水平的分析发现，由于缺乏低阶的同形异形，很少或根本没有支持某些高阶进化枝以及大多数通用和特定的关系。将这一分析应用于Siwalik Group的蛇记录，可在整个剖面中识别出13种分类和形态，随着时间的推移，原始分类学丰富度的增加与样本量的增加部分相关。然而，样本量与菌落因子的比较没有显示任何显着的相关性，除了与 Acrochordus dehmi 记录的沉积环境呈正相关外，这可能反映了完全水生生物分类群的生境偏好。河流运输的差异。分类学丰富度和平等指数显示出10.0至9.0 Ma之间的增加。从生态学角度讲，这代表了从以斜体为主的动物区系向包括多种陆地和半水生物群在内的更多样化，平衡的动物区系的过渡。这种转变通常与干旱的增加和降水季节的增加同时发生，推断这代表了亚洲季风系统的开始，并且可能代表对环境异质性增加的反应。在8.0 Ma和6.5 Ma之间变化的多样性可能与C3–C4的花期过渡有关，但是更精确的关系很难辨别。对化石记录的检查并不能证实先前的世系内系统变化的假说。根据为现存的分类群确定的椎骨长度和口鼻孔长度之间的回归关系，估算的体长为1.5至4.0米，表明。 dehmi 比所有活着的 Acrochordus 大，在整个化石记录中平均身长是一致的。椎骨形状随时间变化的形态计量学分析并未揭示出与系统进化或动物更新相关的假设相一致的模式，但证明了 A。 dehmi 在形态上与现存的 Acrochordus 不同。 A. dehmi 的同质性可能是由于与现存的 Acrochordus 共享的低能量生理导致的，这可以作为应对环境变化的缓冲。

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