Mapping sclerobiosis: a new method for interpreting the distribution, biological implications, and paleoenvironmental significance of sclerobionts on biotic hosts

The use of sclerobiosis as a tool for paleoenvironmental and paleoecological research is undermined by a lack of comparable methods for sclerobiont data collection and analysis. We present a new method for mapping sclerobiont distributions across any host, and offer an example of how the method may be used to interpret sclerobiont data in relation to host orientation. This approach can also be used to assess the suitability of beds and fossil material for paleoenvironmental reconstruction. A sample of 150 encrusted dorsibiconvex atrypide brachiopods were selected from six beds in the Waterways Formation (latest Givetian – Early Frasnian; Alberta, Canada). The dorsal and ventral valves of each brachiopod were photographed. Sclerobiont taxa were mapped onto the photographs, and the maps were used to create stacked images with each of the 25 brachiopod specimens from each bed. Based on the life orientation of dorsibiconvex atrypides, three zones were designated on the host: the post mortem zone, (only available to sclerobionts after death and reorientation of the host); the shaded zone (brachial valve, excluding the post mortem zone); and the exposed zone (ventral valve). Randomization simulation results indicate that all beds likely exhibit non random encrustation patterns, and corroborate the hypotheses that: (1) much of the encrustation occurred while the hosts were alive, and (2) these beds and fossils have experienced little physical reworking or transport and would be suitable for paleoenvironmental analysis. Mapping sclerobionts across hosts can serve as a unifying method to increase the recognition and use of sclerobiosis in paleontological studies.

将硬栖生物研究（sclerobiosis）作为古环境与古生态研究工具的应用，因缺乏统一可比的硬栖生物（sclerobiont）数据采集与分析方法而受到极大制约。本文提出一种可用于绘制任意宿主壳体上硬栖生物分布的新方法，并通过实例展示了如何利用该方法结合宿主生活姿态来解读硬栖生物数据。该方法同样可用于评估地层床层与化石材料是否适用于古环境重建研究。
研究团队从加拿大阿尔伯塔省吉维特阶晚期—弗拉斯阶早期的水道组（Waterways Formation）6个地层床层中，选取了150枚带有附着硬栖生物的背腹双凸型无洞贝目（Atrypide）腕足类标本。对每枚腕足类的背壳与腹壳进行了拍照。
研究人员将硬栖生物类群标注于对应照片之上，并利用这些标注图为每个地层床层的25件腕足类标本分别生成了堆叠图像。
基于背腹双凸型无洞贝目腕足类的生活姿态，研究者在宿主壳体上划定了三个区域：死后带（仅在宿主死亡并发生姿态重定向后，方可被硬栖生物附着的区域）、遮蔽带（腕足类背壳，排除死后带区域）以及暴露带（腕足类腹壳）。
随机化模拟结果显示，所有床层的硬栖生物附着模式均呈现非随机性，验证了两项假说：其一，多数硬栖生物附着事件发生于宿主存活期间；其二，这些床层与化石几乎未经历物理再改造或搬运，适用于古环境分析。
跨宿主壳体的硬栖生物分布绘制方法可作为一种统一的研究手段，提升硬栖生物研究在古生物学研究中的认可度与应用广度。