Data from: Cambrian cinctan echinoderms shed light on feeding in the ancestral deuterostome

Reconstructing the feeding mode of the latest common ancestor of deuterostomes is key to elucidating the early evolution of feeding in chordates and allied phyla; however, it is debated whether the ancestral deuterostome was a tentaculate feeder or a pharyngeal filter feeder. To address this, we evaluated the hydrodynamics of feeding in a group of fossil stem-group echinoderms (cinctans) using computational fluid dynamics. We simulated water flow past three-dimensional digital models of a Cambrian fossil cinctan in a range of possible life positions, adopting both passive tentacular feeding and active pharyngeal filter feeding. The results demonstrate that an orientation with the mouth facing downstream of the current was optimal for drag and lift reduction. Moreover, they show that there was almost no flow to the mouth and associated marginal groove under simulations of passive feeding, whereas considerable flow towards the animal was observed for active feeding, which would have enhanced the transport of suspended particles to the mouth. This strongly suggests that cinctans were active pharyngeal filter feeders, like modern enteropneust hemichordates and urochordates, indicating that the ancestral deuterostome employed a similar feeding strategy.重建后口动物（deuterostomes）最近共同祖先的取食模式，是阐明脊索动物及相关类群取食行为早期演化的核心议题；然而学界对于祖先后口动物究竟为触手型取食者还是咽滤食者（pharyngeal filter feeder），迄今仍存争议。为解决这一学术争议，本研究借助计算流体动力学，对一类化石茎群棘皮动物（cinctans）的取食流体力学特性展开评估。我们针对多种潜在生活姿态，对寒武纪带形动物（cinctans）的三维数字化模型开展绕流模拟实验，同时覆盖被动触手取食与主动咽滤取食两种取食模式。结果显示，当口部朝向水流下游时，可实现阻力与升力的最优降低。此外，模拟数据表明：在被动取食的模拟场景中，几乎无水流抵达口部及与之相连的边缘沟；而在主动取食场景下，则有大量水流朝向动物本体，这将显著促进悬浮颗粒向口部的输送。这一发现有力佐证，带形动物（cinctans）与现代肠鳃纲半索动物、尾索动物一样，属于主动咽滤食者，这也暗示祖先后口动物采用了与之相似的取食策略。