A little walk between Early Jurassic sponges and corals: a confusing morphological convergence.
Résumé
Hispaniastraea Turnšek et Geyer, 1975 is a unique coral genus from the Early Jurassic Epoch (Liassic). Corals of this genus are characterised by a highly dominant major septum and a set of eleven minor septa that are very short or even abortive. Initially discovered in Spain, new samples of this genus were depicted from Morocco by Beauvais in 1980; however, this genus was interpreted as a synonym of Pseudoseptifer Fischer, 1970, a chaetetid sponge (i.e., a sponge with siliceous spicules embedded in a calcareous skeleton). The skeleton of Pseudoseptifer is composed of adjacent tubules that increase by fissiparity by means of a pseudoseptum. Based on the study of new material sampled from the Lower Jurassic of Morocco and Southern France, we highlight the coexistence and legitimacy of both genera (i.e., Pseudoseptifer and Hispaniastraea), which therefore constitutes a fine example of morphological convergence between separate phyla. Although the living tissues and microstructures of the skeleton differ between the sponge and coral genera, the distinction from fossil material is challenging, especially if material is diagenetically altered. Herein, we recommend a set of key characters to distinguish these genera and propose a systematic revision of the genus Hispaniastraea. The synonymy between the two original species, Hispaniastraea murciana and H. ramosa is established and a new species, Hispaniastraea ousriorum, is described. Finally, a new family, the Hispaniastraeidae (Order Hexanthiniaria?), is erected for these distinctive corals, which are unique in the history of this group.