The nature of drilling predation, although well documented for molluscan fossils, is understudied for micromolluscs (<5mm). Studying predation in micromolluscs is especially critical in evaluating the adaptive significance of micromorphy against predation and assessing the importance of predator-prey size relationship (PPSR). This study documents drilling predation event in microbivalves from early Miocene (Burdigalian) fossil assemblage of Quilon limestone from Kerala, India. Our sample of ~2000 valves represent nine families with an average drilling frequency (DF) of 0.06 and an incomplete drilling frequency (IDF) of 0.26. The characteristic drillhole morphology and occurrence of five genera of modern drilling gastropods (Naticid: Natica, Tanea and Polinices; Muricid: Triplex and Dermomurex) from the same locality reveals the predator identity. Predation in the studied assemblage is found to be highly selective in terms of prey taxa, size, mobility and site selection. Six out of nine families show evidence of predation indicating taxon selectivity. Poor correlation between DF and abundance further supports this view. Failed attacks are strongly correlated with morphological features such as surface ornamentation (Lucinidae), presence of conchiolin layers (Corbulidae). Drilling occurs primarily on medium size class and prey outside this size range show lower rate of attack. This indicates the existence of an “inverse size refugia” for extremely small prey along with the classical size refugia existing for large prey. Mobility is found to be a deterrent to drilling predation and it also increases failure. Microbenthos of Quilon limestone shows a lower predation intensity in comparison to the Miocene macrobenthos worldwide including coeval formation of the Kutch Basin. The interaction in microbenthos is more strongly size-dependent in contrast to the Kutch fauna. Reduced predation intensity in microfauna and existence of “inverse size refugia” support the claim of micromorphy acting as a defense mechanism and highlights the role of size-dependent predation in marine benthos.

中文翻译：

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微观形态对钻探捕食的有效性：印度基隆石灰岩中新世早期动物群组合的见解

尽管对软体动物化石有充分的文献记载，但对于微软体动物（<5mm），钻探捕食的性质尚未得到充分研究。在评估微形态对捕食的适应性意义和评估捕食者与猎物大小关系（PPSR）的重要性方面，研究小分子中的捕食尤其关键。这项研究记录了印度喀拉拉邦Quilon石灰岩早期中新世（Burdigalian）化石组合的微双壳类中的钻捕活动。我们的约2000个阀门样本代表9个系列，平均钻探频率（DF）为0.06，不完全钻探频率（IDF）为0.26。现代钻腹足纲动物的五个属（Naticid：Natica，Tanea和Polinices; Muricid：来自同一地点的Triplex和Dermomurex）揭示了捕食者的身份。在猎物类群，大小，活动性和地点选择方面，发现所研究的组合中的捕食具有高度选择性。9个家庭中有6个显示出捕食证据，表明分类群具有选择性。DF和丰度之间的相关性较差进一步支持了这种观点。失败的攻击与形态特征（例如表面装饰（Lucinidae），存在的贝壳杉蛋白层（Corbulidae））密切相关。钻探主要发生在中等大小的动物上，超出此大小范围的猎物显示出较低的攻击率。这表明存在极小的猎物的“逆大小避难所”以及存在于大型猎物的经典大小避难所。人们发现机动性对钻井掠夺性具有威慑作用，并且还会增加失败率。与全球中新世大型底栖动物（包括库奇盆地的同时期形成）相比，基隆石灰岩的微底栖动物显示出较低的捕食强度。与库奇动物区系相反，在底栖动物中的相互作用更强烈地依赖于大小。微动物区系中捕食强度的降低和“逆大小避难所”的存在支持了微形态作为防御机制的主张，并突显了规模依赖性捕食在海洋底栖动物中的作用。