Huang Bing, Rong Jiayu
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China.
Proc Natl Acad Sci U S A. 2025 Jul 29;122(30):e2509354122. doi: 10.1073/pnas.2509354122. Epub 2025 Jul 21.
Understanding the drivers of spatial patterns in fossil communities is fundamental to paleoecology, yet direct evidence for biological mechanisms regulating interindividual spacing remains elusive. Brachiopod setae, hypothesized to function in feeding or defense, are exceedingly rare in the fossil record, especially among post-Cambrian taxa. Here, we present the report of exquisitely preserved setae from an exceptional in situ fossil assemblage of the early Silurian rhynchonelliform brachiopod . Multiproxy analyses (scanning electron microscopy, X-ray fluorescence, and microcomputed tomography) revealed intricate ultrastructural details and diverse taphonomic pathways, leading to a reinterpretation of apparent calcitic preservation as primarily iron oxides with subsequent coating. Critically, the undisturbed nature of this aggregation allowed rigorous spatial point pattern analysis (Nearest-Neighbor Analysis, Thiessen polygons). This revealed a statistically significant, nonrandom, checkerboard-like distribution among individuals within the studied fossil deposit, indicative of active spacing regulation. Strikingly, the measured average interindividual spacing quantitatively relates to the length of the preserved setae. This provides the direct paleontological evidence demonstrating that these subtle morphological structures could have actively mediated spatial organization within a dense benthic community. Our findings illustrate a biological mechanism capable of shaping community structure, operating beyond passive environmental constraints or initial larval settlement preferences, and highlight the potential for subtle anatomical features to exert significant ecological influence in deep time.
了解化石群落空间格局的驱动因素是古生态学的基础，但调节个体间间距的生物学机制的直接证据仍然难以捉摸。腕足动物的刚毛被认为具有摄食或防御功能，在化石记录中极为罕见，尤其是在寒武纪后的类群中。在这里，我们报告了来自早志留世喙壳腕足动物一个特殊原地化石组合中保存精美的刚毛。多方法分析（扫描电子显微镜、X射线荧光和显微计算机断层扫描）揭示了复杂的超微结构细节和多样的埋藏途径，导致将明显的方解石保存重新解释为主要是铁氧化物并随后有涂层。至关重要的是，这种聚集的未受干扰性质允许进行严格的空间点模式分析（最近邻分析、泰森多边形）。这揭示了在所研究的化石沉积物中个体之间存在统计学上显著的、非随机的、棋盘状分布，表明存在主动的间距调节。引人注目的是，测量的平均个体间间距在数量上与保存的刚毛长度相关。这提供了直接的古生物学证据，证明这些细微的形态结构可能在一个密集的底栖生物群落中积极介导了空间组织。我们的发现说明了一种能够塑造群落结构的生物学机制，它超越了被动的环境限制或初始幼虫定居偏好而起作用，并强调了细微解剖特征在地质历史时期发挥重大生态影响的潜力。
