The Late Devonian ammonoid species Acrimeroceras falcisulcatum and A. stella have similar-shaped discoidal adult conchs. Their conch morphology and its ontogenetic development are described and analysed. Despite great similarities in their adult conch morphology, they can be clearly distinguished by differences in the shape of their juvenile whorl profile and by the growth trajectories of their cardinal conch parameters: conch width index, umbilical width index and whorl expansion rate. Quantification of ontogenetic change in the two species demonstrates that the stratigraphically younger species A. falcisulcatum possesses the less complex ontogeny compared to the stratigraphically older A. stella. The closely related genus Paratornoceras (early Famennian) and the unrelated Late Viséan Calygirtyoceras show juvenile conch morphology and ontogenetic trajectories very similar to Acrimeroceras stella. This similarity can be seen as iterative independent unfolding of homoplastic characters, possibly linked to size-dependence of the functional morphology of the conchs.

中文翻译：

---

盘状晚泥盆纪氨Ac虫盘状菌的多相个体发育。

泥盆纪晚期的氨类物种Acrimeroceras falcisulcatum和A. stella具有类似形状的盘状成虫海螺。描述和分析了它们的海螺形态及其个体发育。尽管它们的成年海螺形态有很多相似之处，但可以通过其幼年轮生轮廓的形状差异和主要海螺参数的生长轨迹（海螺宽度指数，脐带宽度指数和轮生膨胀率）来清楚地区分它们。定量的两种个体的个体发生变化表明，与地层学年龄较大的A. stella相比，地层学较年轻的物种A. falcisulcatum具有较少的个体发育。密切相关的属伞旁龙（Famennian早期）和不相关的晚维森珊瑚礁（ViséanCalygirtyoceras）表现出的幼海螺形态和个体发育轨迹与恒星蛤rim非常相似。这种相似性可以看作是同质性状的迭代独立展开，可能与海螺功能形态的大小相关。