Exceptional basal-body preservation in some Early Triassic conodont elements from Oman

Abstract

Conodont elements are composed of two main parts: the crown and the basal body. The basal body of a conodont element is a laminated structure that is less densely mineralized than the crown and, as a result, is rarely preserved. Elements with preserved basal bodies are found only in exceptional cases in the fossil record. To date, no S or M element with preserved basal body has ever been documented for post-Devonian conodonts, which had raised the question of an evolutionary trend towards unmineralized basal bodies in conodonts. Here we report the discovery, in Smithian (Early Triassic) rocks of Oman, of neospathodid conodont elements whose basal body is partly preserved. We demonstrate the presence of basal body in all elements, including S and M elements, of Novispathodus, and most likely of all gondolelloideans, thereby suggesting that the absence of basal bodies in post-Devonian conodonts was due to a preservational bias only. We further demonstrate that the morphology and extent of the basal bodies in Novispathodus are in agreement with previous predictions and do not contradict a cyclostome-like functional model of the apparatus. Based on a review of the occurrences of basal bodies in the literature, we suggest a general pattern for the morphology of the basal bodies in conodont elements that may reflect the mechanical constraints associated with feeding motions.