A COMPARISON OF PRE-AND POST-EXTINCTION SCLEROBIONT COMMUNITIES ACROSS THE LATE DEVONIAN MASS EXTINCTION IN NORTH AMERICA
In general, taxon richness and abundance of brachiopod-encrusting sclerobionts markedly declined. Branching colonial encrusters were greatly reduced; auloporid corals went extinct, and hederellids became a rare component in most Mississippian sclerobiont communities. Among common Devonian solitary encrusters, cornulitids remained abundant sclerobionts in many Mississippian communities, whereas microconchids often were a smaller proportion of the fauna. Craniate brachiopods and solitary rugose corals remained a minor component of post-extinction sclerobiont communities. Encrusting, sheet-like bryozoans became a more conspicuous portion of the Mississippian sclerobiont fauna, in that they filled a greater proportion of the sclerobiont fauna and occurred in more communities than those in the Devonian.
Most Devonian brachiopod faunas were dominated by finely-ribbed brachiopods, such as atrypids and stropheodonts, whereas smooth and spinose athyrids and productids were common components in benthic Mississippian ecosystems. Meanwhile, spiriferids were common in both pre- and post-extinction communities. Surviving sclerobiont lineages had to contend with changes in substrate morphology and availability.
Despite major pre- and post-extinction differences, several features established in pre-extinction sclerobiont faunas carried over into the Mississippian: (1) sclerobionts continued to preferentially encrust certain shell textures over others by shifting to new brachiopod taxa rather than generalizing on all available substrates; (2) some sclerobiont taxa remained specialists in the commissure-proximal niche; (3) based on preserved, calcified forms, apparent spatial competition was low in most communities; and (4) sclerobiont richness among communities was not controlled by the composition of the brachiopod fauna, but likely by other processes such as larval recruitment.