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We examine the preservation, autecology and morphological variation for several characters of the Cretaceous gonorynchiform fish Dastilbe from the Lower Cretaceous of Brazil and Africa. More than 83 specimens were examined. We test species validity using characters of the caudal endoskeleton and meristic counts of fin-rays vs length. Evidence provided by fossilized soft tissues and slabs containing large individuals ‘freeze framed’ in the process of swallowing smaller prey meals, show that Dastilbe was predatory, at least as adults, as well as cannibalistic. Dastilbe was probably an anadromous fish tolerant of hypersalinity and in Araripe was subjected to frequent mass mortality events. Observations of the otic region indicate that the lagenar statolith is consistently larger than the saccular statolith, hence revealing a primitive actinopterygian condition. For the first time, a lagenar statolith from Dastilbe has been cleaved to expose putative annuli-like ridges. Our results clearly show that there is a wide degree of morphological plasticity of the endoskeleton coupled with wide meristic variation, and as such, overall length, fin-ray count and even absence or presence of caudal diastema are not suitable criteria for species recognition in Dastilbe. New specimens from the Crato Formation (Aptian) and statistical tests suggest rejection of all species of Dastilbe erected subsequent to Jordan (1910). All Brazilian specimens of Lower Cretaceous Dastilbe can be assigned to the single species D. crandalli Jordan. The African D. batai Gayet is also placed within D. crandalli