Article: Constructional morphology and palaeoecological significance of three Late Jurassic regular echinoids

General shape of test, spine and tubercle morphologies, and ambulacral pore characteristics of three regular echinoid species from the Upper Jurassic are interpreted in functional terms. Results are compared with independent sedimentological and palaeoecological analyses of the host sediments. In Acrocidaris nobilis the existence of a basal P3/4 isopore phyllode suggests the development of a strong sucker disc which enabled firm attachment in a high energy hardground setting. This interpretation is corroborated by tubercle characteristics indicating firmly attached but largely immotile spines, forming a 'secondary test'. Morphological interpretation of Rhabdocidaris rhodani suggests a low energy, possibly partly dysaerobic, firmground setting as evidenced by (1) the exclusive occurrence of slit-like C isopores and (2) oblique tubercles with a broad muscle attachment area indicating strong, motile stalking spines. Flattened general shape, lack of aboral spines and a fairly strong sucker disc enabled Glypticus hieroglyphicus to crawl across very irregular topography and even browse on the undersides of corals or within an open coral framework. On the other hand, the fairly massive test suggests that elevated water energy occurred at least occasionally, so that the host oligospecific dish-shaped coral association was probably positioned at shallower depths than previously thought. It is suggested that the adaptations of some Late Jurassic regular echinoids to variable niches independently accompanied and mirrored similar adaptive strategies developed in irregular echinoids, such as the evolution of respiratory flattened tube feet or adaptations towards sedimentation.