Ordovician Rugosans likely originated from a non-skeletal anthozoan similar to modern
sea anemones. The oldest rugosan fossils appear near the end of the
Middle Ordovician, during the transition from the
Darriwilian stage to the
Sandbian stage at the start of the
Late Ordovician.
Lambelasma, a calostyline from Darriwilian-age
Iran, is the earliest confirmed example. By the end of the Sandbian stage, rugose corals were common in the shallow seas of
North America and
Baltoscandia. Five rugosan suborders filled out the reef-building faunas of the Late Ordovician: Cystiphyllina, Calostylina, Stauriina, Streptelasmatina, and Metriophyllina. Cystiphyllines, streptelasmatines, and metriophyllines were usually solitary, stauriines were colonial, and calostylines included many species of both solitary and colonial corals. Some early rugosans were very simple, such as
Primitophyllum (a cystiphylline) and
Lambeophyllum (a calostyline). These simple forms resembled tiny cones with rudimentary septa and no tabulae, and they may be a good estimate for an ancestral rugosan. Others were more typical, such as the solitary
Streptelasma (a streptelasmatine) and colonial
Favistina (a stauriine).
Silurian The Ordovician suborders all persisted into the
Silurian, though newer groups achieved even greater abundance. The Arachnophyllina, Ketophyllina, and Lycophyllina diversify quickly, while others (the Columnariina, Cyathophyllina, and Ptenophyllina) slowly take hold. Calostylines diminish and go extinct near the Silurian-Devonian boundary. Lycophyllines were usually solitary, while arachnophyllines, columnariines, and ptenophyllines were usually colonial. Cyathophyllines and ketophyllines included many solitary and colonial species.
Devonian The
Early Devonian was the apex of diversity for rugosans and many other marine animals. The
Middle to
Late Devonian, however, saw a series of extinction events which profoundly reshaped rugosan faunas. Arachnophyllines, cystiphyllines, lycophyllines, and streptelasmatines all die out near the start of the Late Devonian. Others (ketophyllines, columnariines, and ptenophyllines) last longer, though they too would vanish by the end of the period. However, the Devonian was also the origin of a few more rugosan suborders: Plerophyllina and Stereolasmatina, both of which were small and solitary.
Carboniferous-Permian Rugosans recovered from extinction quickly in the
Mississippian (early
Carboniferous). Plerophyllines and stereolasmatines lead the charge, alongside a substantial diversification of four new suborders: Aulophyllina, Caniniina, Lithostrotionina, and Lonsdaleiina. Aulophyllines and caniniines were usually large and solitary, while lithostrotionines and lonsdaleiines were usually colonial.
An extinction at the end of the Mississippian eliminated the last stauriines and cyathophyllines, while the other suborders survived at a slightly reduced capacity through the
Pennsylvanian (late Carboniferous). Rugosans experienced a few small extinctions within the Permian period, but on the whole they were still abundant reef builders until the entire class died out during the
Permian-Triassic mass extinction. == Gallery ==