Ecology, evolution, distribution and population of Hexagonaria in Western Europe

The record of Hexagonarta in the Lower and Middle Devonian shows that only slow rates of change occurred at these times, whereas in Frasnian time there occurred complex diversity and speciation patterns. Very rapid faunal changes and mass extinctions in corals have been observed near the boundary of Middle Devonian and Upper Devonian and at the end of Fr 1 time. Based on the study of population variation, ecological variation and phylogenetic lineage, the complete evolutionary patterns of Hexagonaria can be traced in the Givetian and Frasnian. The evolutionary patterns observed in different facies demonstrate that: 1. most changes in diversity and speciation were strictly related to differences in the biology of species adapted to different or changing environments, 2. the critical factors in encouraging diversification of species appear to be a combination of ecologic conditions and paleogeographic situations, 3. some parallel evolutions were independent of environments and paleogeographic isolation but were due to time

Heliolitid corals and their competitors: a case study from the Wellin patch reefs, Middle Devonian, Belgium

peer reviewedWellin patch reefs are small Upper Eifelian build?ups within the fine?grained argillaceous limestone of the Hanonet Formation. Whereas the reefs themselves are not well exposed, their fossil assemblage is accessible in the hills near the town of Wellin, approximately 40xA0km SE of Dinant in Belgium. It is especially rich in massive stromatoporoids, heliolitids and other tabulate corals. They exhibit predominantly domical and bulbous morphologies. This paper focuses primarily on the palaeoautoecology of the heliolitid corals and their relationships with other organisms. Cases of mutual overgrowth between heliolitids, other corals and stromatoporids suggest a high degree of competition for space on the reefs, possibly related to the scarcity of hard substrates. Coral and stromatoporoid growth forms, as well as the prevalence of micritic matrix, point to a relatively low energy environment. However, abundant growth interruption surfaces, sediment intercalations and rejuvenations of corals suggest episodically increased hydrodynamic regime and sediment supply. It is inferred that the patch reefs developed in a relatively shallow environment, where the reefal assemblage was regularly affected by storms. Heliolitids exhibited high sediment tolerance and relied on passive sediment removal for survival. They also could regenerate effectively and commonly overgrew their epibionts, after the colony’s growth was hampered by the sediment. This is recorded in extremely abundant growth interruption surfaces, which allow the analysis of the impact of sediment influxes on the heliolitid corals. ? 2021 Lethaia Foundation. Published by John Wiley & Sons Lt