Published online by Cambridge University Press: 21 July 2017
Within a family, genera are usually separated on the basis of their colonial structure. The periodic occurrence of transgeneric highly variable specific units (spectra) in the fossil record poses nomenclatural and phylogenetic problems. A detailed example among Jurassic montlivaltiids is presented in this paper involving the genera Montlivaltia, Coenotheca, Thecosmilia, Latiphyllia and Complexastrea. These spectra are related to peculiar unstable nonreefal environments and are characterized by the dominance of young stages of the colonial growth (astogeny). The arising nomenclatural difficulties are solved by way of spectral nomenclature which allows naming morphological types, as well as taxonomic units and keeping some stability within the general frame of nominal taxa. Genera correspond to grades (solitary, thamnasterioid, phaceloid, meandroid, cerioid) rather than clades and the colonial structure is a labile character. Several alternative phylogenetic hypotheses are proposed, among which, some can renew our vision of this group and emphasize that the iterative production of generic-level shapes is best explained by mean of heterochronic processes. It is suggested that testing of these hypotheses be extended to other families such as Microsolenidae, Stylophyllidae or Fungiidae.