Belemnites are an extinct group of Mesozoic coleoid cephalopods with a fossil record ranging from the early Late Triassic [about 240 million years ago (Mya)] to the Cretaceous/Palaeogene boundary (65 Mya). Belemnites were widely distributed, highly abundant and diverse, and an important component of Mesozoic marine food webs. Their internal shells, specifically their low‐Mg calcite rostra, have been used as palaeoenvironmental carbonate archives for the last 70 years. This is primarily due to the assumption that the rostrum calcite formed in equilibrium with the oxygen isotope composition of ambient sea water. Of prime importance for the reliable interpretation of isotope data derived from these biogenic carbonates is a robust reconstruction of the palaeobiology of their producers. Here we provide a critical assessment of published reconstructions of belemnite soft‐body organization and their lifestyle and habitats. Different lines of evidence, including sedimentological, geochemical, morphological, and biomechanical data, point towards an outer shelf habitat of belemnites, for some taxa also including the littoral area. Belemnite habitat temperatures, oxygen content, salinities, and life span are constrained based on observations of the ecology and life history of modern coleoids. Belemnite habitat depth might have been largely controlled by food and temperature, with a temperature optimum between 10°C and 30°C. The distribution of modern coleoids is for most species restricted to well‐oxygenated water masses and a salinity between 27 and 37 psu. The trophic position of belemnites as both predators and prey is documented by unique fossil finds of stomach contents and soft tissue preservation, such as jaws, hooks, and ink sacs. Belemnites were medium‐sized predators in the epipelagic zone (not deeper than ∼200 m) hunting for crustaceans, other cephalopods, and fishes. Taxa with elongated rostra probably were fast and highly manoeuvrable swimmers. Forms with conical rostra represent slow but highly manoeuvrable swimmers, and forms with depressed rostra likely had a bottom‐related life habit. Predators of adult belemnites were sharks, bony fishes, and marine reptiles. Belemnites, like most of the modern coleoids, were relatively short lived, most likely living only for 1–2 years. Understanding the biomineralization of belemnite rostra is highly relevant for an improved interpretation of their geochemistry. Here we confirm that belemnite rostra are composed of low Mg‐calcite fibres, but they do not contain distinct types of laminae. These fibres are composed of two distinct calcite phases. One phase is a filigree network of tetrahedral organic‐rich calcite and the second phase is represented by organic‐poor calcite.

中文翻译：

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箭石古生物学——讲台地球化学解释的基础

箭石是一类已灭绝的中生代鞘状头足类动物，其化石记录范围从晚三叠世早期 [约 2.4 亿年前 (Mya)] 到白垩纪/古近纪边界 (65 Mya)。箭石分布广泛、丰富多样，是中生代海洋食物网的重要组成部分。在过去的 70 年里，它们的内壳，特别是它们的低镁方解石喙，已被用作古环境碳酸盐档案。这主要是由于假设形成的讲台方解石与周围海水的氧同位素组成达到平衡。对于从这些生物碳酸盐中提取的同位素数据的可靠解释，最重要的是对其生产者的古生物学进行强有力的重建。在这里，我们对已发表的箭石软体组织及其生活方式和栖息地的重建进行了批判性评估。不同的证据，包括沉积学、地球化学、形态学和生物力学数据，都指向箭石的外陆架栖息地，对于一些分类群也包括沿海地区。箭石的栖息地温度、含氧量、盐度和寿命受到对现代珊瑚虫的生态学和生活史的观察的限制。箭石的栖息地深度可能在很大程度上受食物和温度的控制，最佳温度在 10°C 到 30°C 之间。对于大多数物种来说，现代胶体的分布仅限于充氧良好的水团和 27 至 37 psu 之间的盐度。箭石作为捕食者和猎物的营养地位被胃内容物和软组织保存的独特化石发现所记录，例如颚、钩和墨囊。箭石是上层带（不深于 200 米）的中型捕食者，捕食甲壳类动物、其他头足类动物和鱼类。具有细长喙的类群可能是速度快且机动性强的游泳者。具有圆锥形嘴的形式代表速度慢但机动性强的游泳者，而具有凹陷嘴的形式可能具有与底部相关的生活习惯。成年箭石的天敌是鲨鱼、硬骨鱼和海洋爬行动物。箭石，像大多数现代的鞘状体一样，寿命相对较短，很可能只能活 1-2 年。了解箭石 rostra 的生物矿化作用与改进对其地球化学的解释高度相关。在这里，我们确认箭石喙由低镁方解石纤维组成，但它们不包含不同类型的纹层。这些纤维由两个不同的方解石相组成。一相是富含有机物的四面体方解石的丝状网络，第二相以贫有机物的方解石为代表。