Ontogenic trajectories recorded within the fossilized calcite tests of planktic foraminifera are significant for understanding their paleoecology and evolution. High-resolution 3-D imaging techniques enable quantitative measurement of test calcite and enclosed cavity volumes allowing a detailed characterization of the ontogenetic variations in the biomass to calcite ratio. Here we used micro-CT scanning to inspect ontogenetic variations among four globorotaliform planktic foraminiferal morphospecies from the late Miocene of International Ocean Discovery Program Site U1490 in the tropical Western Pacific. A conservative log-linear growth pattern is observed for all specimens. The proloculus size has an important control on the growth trajectory of the inspected specimens, and specimens with smaller proloculus volume generally have more chambers at the end of their life. The overall pattern of deviations from the log-linear growth trajectory among inspected specimens is well constrained, which varies between different groups in magnitude. The ontogenetic mean density, which is proposed here as an indicator of the degree of difficulty in producing positive buoyancy, shows a generally decreasing trend before the terminal stage in all specimens. We propose that the decreasing mean density (MD) as the test enlarges is an important adaption for planktic foraminifera to maintain an optimal habitat for nutrition and reproduction. The value of the mean density at the two-chambered stage exhibits a linear relationship with chamber volumes among inspected specimens with different habitats and different coiling forms, for which the ecological implications are explored.

浮游有孔虫化石方解石试验中记录的本体论轨迹对于了解其古生态和演化意义重大。高分辨率3D成像技术可对测试方解石和封闭的空腔体积进行定量测量，从而能够详细表征生物质与方解石比例的本体变化。在这里，我们使用微CT扫描检查了来自热带西太平洋国际海洋发现计划站点U1490中新世晚期的四种球状滑石板状有孔虫形态物种之间的成因变异。所有标本均观察到保守的对数线性增长模式。牙lo的大小对被检标本的生长轨迹有重要的控制，lo孔较小的标本在其使用寿命结束时通常会容纳更多的腔室。受检样本中与对数线性增长轨迹的偏差的总体模式受到很好的约束，其大小在不同组之间有所不同。这里提出的个体发育平均密度是产生正浮力的难易程度的一个指标，在所有样本的末期之前，个体平均密度呈现出总体下降的趋势。我们建议，随着测试的扩大，平均密度的降低是对板状有孔虫的重要适应，以保持最佳的营养和繁殖环境。在两个腔室阶段的平均密度值与具有不同栖息地和不同卷曲形式的被检标本之间的腔室体积呈线性关系，