Evolution trends in Middle Carboniferous Petalaxidae (Rugosa)

Various aspects of the study of the Petalaxidae Fomichev, 1953 are considered. Detailed observations from previous investigations together with new, more precise data on the stratigraphic distribution of the Petalaxidae in the northern and central part of the Russian Platform are used as a framework for phylogenetic reconstruction. Five main morphological groups are recognized within Petalaxis Milne Edwards et Haime, 1852, based on the combination of stable and variable features predominant in each group. The main trend in Petalaxidae evolution during the Bashkirian and Moscovian stages is an increase in the colony integration and the stabilization of multitrabecular septal structure. The diagnosis and species content are given for taxa included in Petalaxidae after authors revision. Four new taxa are described: Donastraea n.g., Ivanovia (Procystophora) n.sg., Petalaxis (Petelaxis) primitivum n.sp. and P. (P. ) gigas n.sp.