Thalattosuchian crocodylomorphs were a ubiquitous component of shallow marine ecosystems during the Jurassic and Early Cretaceous. Alas, their origins remain a mystery. Here we describe three specimens from the Sinemurian (and possibly Early Pliensbachian) of the UK: a partial cranial rostrum, a series of cervical vertebrae, and two dorsal vertebrae adhered with matrix. These specimens are amongst the oldest known thalattosuchian fossils, with the partial cranial rostrum being the oldest known non-neothalattosuchian thalattosuchian. This partial cranial rostrum has a unique combination of rostral characters never seen before in any crocodylomorph, and helps to elucidate early thalattosuchian internal rostrum evolution, suggesting that the reduction in thalattosuchian paranasal sinuses was not related to either the reorganization of rostral neurovasculature seen in later diverging taxa or the increased cancellous bone microstructure. Based on our CT sample, a shift in cranial bone microstructure occurred in the Eoneustes + Metriorhynchidae subclade, one that coincided with the enlargement of the salt glands and decoupling of the external antorbital fenestra from the paranasal sinuses. Without extensive histological sampling we cannot determine whether the shift to an obligate aquatic lifestyle occurred prior to the evolution of Metriorhynchidae.

中文翻译：

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来自英国 Sinemurian（早侏罗世）的海鳄亚目鳄鱼


海鳄类鳄鱼是侏罗纪和早白垩世浅海生态系统中普遍存在的组成部分。唉，它们的起源仍然是个谜。在这里，我们描述了来自英国斯尼莫阶（可能还有早期普林斯巴阶）的三个标本：部分颅骨、一系列颈椎和两块粘有基质的背椎。这些标本是已知最古老的海鳄类化石之一，其中部分颅骨是已知最古老的非新海鳄类化石。这个部分颅吻部具有在任何鳄形类动物中从未见过的独特的吻部特征组合，有助于阐明早期丘鳄内部吻部的进化，表明丘鳄鼻旁窦的减少与后来分化中看到的吻部神经脉管系统的重组无关。类群或增加的松质骨微结构。根据我们的 CT 样本，Eoneustes + Metriorhynchidae 亚支的颅骨微结构发生了变化，这一变化与盐腺的增大以及眶外窗与鼻旁窦的脱钩同时发生。如果没有广泛的组织学采样，我们无法确定向专性水生生活方式的转变是否发生在Metriorhynchidae进化之前。