Abstract Dinoflagellates and coccolithophores are two of the most important groups of phytoplankton in the modern oceans. These groups originated in the Triassic and radiated through the early Mesozoic, rising to ecological prominence. Within this long-term radiation, important short-term intervals of evolutionary and ecological change can be recognised. The Bajocian (Middle Jurassic, ~170–168 Ma) was characterised by an important ecological transition within the coccolithophores, and the radiation of one of the principal families of cyst-forming dinoflagellates, the Gonyaulacaceae. During the Early Bajocian, the coccolith genus Watznaueria diversified and expanded ecologically to dominate coccolith floras, a situation which continued for the remainder of the Mesozoic. This pattern was paralleled within dinoflagellate cyst floras by the ecological dominance of the genus Dissiliodinium in the mid-palaeolatitudes. These phenomena appear to be linked to a positive carbon isotope shift, and an interval of enhanced productivity driven by a shift to a more humid climate, enhanced continental weathering and nutrient flux, or by changes in ocean circulation and upwelling. The latest Early Bajocian to earliest Bathonian was then characterised by the rapid increase in diversity of dinoflagellate cysts within the family Gonyaulacaceae. Through this interval, the Gonyaulacaceae transitioned from being a relatively minor component of dinoflagellate cyst floras, to becoming one of the prominent groups of cyst-forming dinoflagellates, which has persisted to the Holocene. In Europe, the pattern of this radiation was strongly influenced by sea level, with the increase in gonyaulacacean diversity reflecting a major second-order transgression. On a finer scale, the main pulses of first appearances correlate with third-order transgressive episodes. A rise in sea level, coupled with changes in the tectonic configuration of ocean gateways, appears to have controlled the pattern of plankton diversification in Europe. These palaeoceanographic changes may have enhanced water-mass transfer between Europe, the northwest Tethys Ocean and the Hispanic Corridor, which promoted the floral interchange of dinoflagellates. Whilst sea-level rise and associated large-scale palaeoenvironmental shifts appear to have controlled the pattern of dinoflagellate cyst appearances in several regions outside Europe, there is no direct correlation between dinoflagellate cyst diversity and sea-level rise on a global scale. Although the Bajocian was transgressive in several regions, widespread flooded continental area was also present throughout the preceding Aalenian, an interval of low gonyaulacacean diversity. Moreover, although the Middle Jurassic was an interval of major climatic cooling, there was a ~5 myr gap between the onset of cooling and the radiation of gonyaulacaceans during the Bajocian. The Bajocian was, however, marked by a major evolutionary radiation in the pelagic realm, including ammonites, giant suspension feeding fishes and planktonic foraminifera. These phenomena may indicate an underlying ecological driver to the radiation of dinoflagellates during the Bajocian evolutionary explosion which could represent an extension of the Mesozoic Marine Revolution.

中文翻译：

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Bajocian（中侏罗纪）：早期中生代浮游植物辐射的关键区间

摘要 甲藻和球石藻是现代海洋中两个最重要的浮游植物群。这些族群起源于三叠纪，辐射到中生代早期，上升到生态显着地位。在这种长期辐射中，可以识别进化和生态变化的重要短期间隔。Bajocian（中侏罗纪，~170-168 Ma）的特征是球石藻内的重要生态转变，以及形成囊肿的甲藻的主要家族之一，Gonyaulacaceae 的辐射。在早巴约世，颗石属 Watznaueria 多样化并在生态上扩张以主宰颗石植物群，这种情况在中生代的剩余时间里一直持续。由于 Dissiliodinium 属在中古纬度的生态优势，这种模式在甲藻孢囊菌群中是平行的。这些现象似乎与碳同位素正转移，以及由转向更潮湿的气候、大陆风化和养分通量增强或海洋环流和上升流变化驱动的生产力增强区间有关。最新的早期巴约阶至最早的巴松阶的特征是 Gonyaulacaceae 科中甲藻囊肿的多样性迅速增加。在这段时间里，Gonyaulacaceae 从甲藻孢囊菌群的一个相对较少的组成部分转变为形成孢囊的甲藻的突出群之一，并一直持续到全新世。在欧洲，这种辐射的模式受到海平面的强烈影响，角龙科动物多样性的增加反映了主要的二级海侵。在更精细的尺度上，首次出现的主要脉冲与三阶海侵事件相关。海平面上升，加上海洋门户构造结构的变化，似乎控制了欧洲浮游生物多样化的模式。这些古海洋学变化可能增强了欧洲、西北特提斯洋和西班牙走廊之间的水团转移，促进了甲藻的花卉互换。虽然海平面上升和相关的大规模古环境变化似乎控制了欧洲以外几个地区的甲藻囊肿出现的模式，在全球范围内，甲藻囊肿多样性与海平面上升之间没有直接关联。尽管 Bajocian 在几个地区发生了海侵，但在之前的 Aalenian 中也存在广泛的淹没大陆区域，这是一个低角龙科动物多样性的区间。此外，虽然中侏罗世是主要气候变冷的间隔，但在巴约纪期间，变冷的开始与角龙科动物的辐射之间存在约 5 米的差距。然而，Bajocian 以远洋领域的主要进化辐射为标志，包括菊石、巨型悬浮摄食鱼类和浮游有孔虫。