The Reengineering of Reef Habitats During the Great Ordovician Biodiversification Event

Abstract

Bryozoans, stromatoporoid sponges, and tabulate corals, all colonial metazoans with lamellar, encrusting growth forms, developed and simultaneously diversified during the Great Ordovician Biodiversification Event (GOBE). After revisiting some classic Lower, Middle, and Upper Ordovician reef localities in Laurentia (Franklin Mountains, west Texas, Mingan Islands in eastern Canada, and Champlain Valley in northeastern United States) and Baltica (northern Estonia) and reviewing the literature, we demonstrate that during the Ordovician a newly emerging consortium of sheet-like bryozoans, stromatoporoid sponges, and tabulate corals locally bound together by microbes, automicrite, and cement and solidly rooted in sediment became the dominant reef-builders globally. The diversification of these sheet-like metazoans (SLM), however, clearly lagged behind the first appearance of their respective skeletal ancestors. Their habitat expansion can be exemplified as a case of simultaneous ecological fitting and 2 ecosystem engineering when the independently evolved shared traits were simultaneously coopted and became advantageous under globally different environmental conditions. This interaction led to the evolutionary diversification of colonial metazoans during the GOBE and to the expansion of novel reef habitats in previously soft-surface settings; a transformation that forever changed marine reefal ecosystems.

The ‘classic stromatolite’ Cryptozoön is a keratose sponge‐microbial consortium

“…128). From this perspective, Cryptozoön can be considered a forerunner of the laminar intergrowth that was a key strategy of reef formation in the Mid–Late Ordovician (Fagerstrom, 1987, p. 344; Kröger et al., 2017, p. 597) and continues to the present day (Riding, 2002b).…”

Lipid biomarker and stable isotopic profiles through Early-Middle Ordovician carbonates from Spitsbergen, Norway

“…During the GOBE, many of the groups that dominated marine ecosystems until the Permian-Triassic mass extinction diversified and rose to ecological dominance. The diversification was accompanied by a variety of major ecological changes including i) increased tiering of benthic ecosystems (Bottjer & Ausich, 1986), ii) re-establishment of metazoandominated reefs (Kröger et al, 2017a), iii) expansion of nektonic and pelagic ecosystems (Servais et al, 2008;Kröger et al, 2009;Servais et al, 2015), and iv) establishment of a latitudinal diversity gradient (Kröger, 2018). Although the timing of diversification varied across clades and from region to region, much of the diversity increase occurred during the Early and Middle Ordovician, especially between the Dapingian (470 Ma) and Darriwilian (467 Ma) stages (Miller & Foote, 1996;Miller, 1997;Droser & Finnegan, 2003;Rasmussen et al, 2016;Trubovitz & Stigall, 2016;Kröger, 2018).…”

Skeletal marine animal biodiversity is built by families with long macroevolutionary lag times

“…via exaptations 19 ) eventually resulting in what has been termed a long phylogenetic fuse 20 , or macroevolutionary lag-time 21,22 . These taxa gained ecological opportunities on geological time scales, triggered by adaptive zone changes 23,24 . Thus, in this model, short macroevolutionary lag time is associated with organismic novelty causing an initial rise of these families in occupancy and diversity, and long macroevolutionary lag times with ecosystems' changing capacities to accommodate members of older, pre-existing families.…”