Saleh F et al. (2022), Contrasting Early Ordovician assembly patterns ...

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Sci Rep 2022 Oct 28;121:3852. doi: 10.1038/s41598-022-07822-z.

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Contrasting Early Ordovician assembly patterns highlight the complex initial stages of the Ordovician Radiation.

Saleh F , Guenser P , Gibert C , Balseiro D , Serra F , Waisfeld BG , Antcliffe JB , Daley AC , Mángano MG , Buatois LA , Ma X , Vizcaïno D , Lefebvre B .

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The Early Ordovician is a key interval for our understanding of the evolution of life on Earth as it lays at the transition between the Cambrian Explosion and the Ordovician Radiation and because the fossil record of the late Cambrian is scarce. In this study, assembly processes of Early Ordovician trilobite and echinoderm communities from the Central Anti-Atlas (Morocco), the Montagne Noire (France), and the Cordillera Oriental (Argentina) are explored. The results show that dispersal increased diachronically in trilobite communities during the Early Ordovician. Dispersal did not increase for echinoderms. Dispersal was most probably proximally triggered by the planktic revolution, the fall in seawater temperatures, changes in oceanic circulation, with an overall control by tectonic frameworks and phylogenetic constraints. The diachronous increase in dispersal within trilobite communities in the Early Ordovician highlights the complexity of ecosystem structuring during the early stages of the Ordovician Radiation. As Early Ordovician regional dispersal was followed by well-documented continental dispersal in the Middle/Late Ordovician, it is possible to consider that alongside a global increase in taxonomic richness, the Ordovician Radiation is also characterized by a gradual increase in dispersal.

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	Figure 1. (a) Stratigraphic correlations between the Central Anti-Atlas (CAA), the Montagne Noire (MN), and the Cordillera Oriental (CO). The studied intervals within this work are highlighted in orange. Note that for the Fezouata Shale orange intervals were not selectively chosen, as those are the only ones yielding echinoderm and trilobite fossils. Se. = Series, St. = Stage, TS = Time Slices27; Morocco28; Cordillera Oriental19; Montagne Noire14. (b) Paleogeography of the three regions; modified from Saleh et al.23.
	Figure 2. Early Ordovician trilobites from the Central Anti-Atlas (a–d), the Montagne Noire (e,f), and the Cordillera Oritental (g,h) in addition to Early Ordovician echinoderms from the Central Anti-Atlas (i–l), and the Montagne Noire (m–p). (a) Euloma sp., late Tremadocian; AA.TGR1c.OI.232, (b) Platypeltoides magrebiensis, late Tremadocian; AA.TGR0a.OI.132, (c) Bavarilla zemmourensis, late Tremadocian; AA.BIZ15.OI.16, (d) Anacheirurus adserai, late Tremadocian; AA.BIZ15.OI.291, (e) Euloma filacovi, late Tremadocian; UCBL-FSL 740109, (f) Paramegalaspis immarginata, late Tremadocian; UCBL-FSL 740027, (g) Pliomeridius sulcatus, middle Floian; CEGH-UNC-16311, (h) Leptoplastides granulosa; middle Tremadocian, CEGH-UNC-21324, (i) Villebrunaster sp., late Tremadocian; FSL 424 961, (j) Macrocystella bohemica, late Tremadocian, MHNM.15690.196, (k) Eocrinoidea indet., late Tremadocian; MHNM.15690.141, (l) Cornuta n. gen. n. sp. cf. "Phyllocystis" jingxiensis; FSL.712971, (m), Villebrunaster thorali, late Tremadocian; UCBL-FSL 168673, (n) Macrocystella azaisi, late Tremadocian; MBB-GG50, (o) Aethocrinus moorei, late Tremadocian; MNHN.A49684, (p) Phyllocystis blayaci, late Tremadocian; UCBL-FSL 168703. 1 cm scale bars (a–f; i–p), magnification = 0.8× (g) and 1.8× (h). Abbreviations (repositories): AA Cadi-Ayyad University, Marrakesh (Morocco), MBB Musée du Biterrois, Béziers (France), MNHN Muséum National d'Histoire Naturelle, Paris (France), UCBL-FSL palaeontological collections, Lyon 1 University, Villeurbanne (France), CEGH-UNC Universidad Nacional de Córdoba, Córdoba (Argentina).
	Figure 3. Niche- versus Dispersal-assembly perspectives. (a) In a niche-assembly scenario, communities are closed and balanced, built by a limited number of species at equilibrium (similar assemblages at t + 1 and t + 2). Niche taxonomic composition is controlled by deterministic (i.e., non-random) biotic interactions between taxa and their environment. (b) Dispersal-assembly scenario in which communities are constantly changing (i.e., non-equilibrium; different assemblages between t + 1 and t + 2) owing to random processes such as migrations.
	Figure 4. (a) Estimation of the sampling effort [observed sampling (Sobs) over extrapolated sampling (Sex)] of echinoderms (echino) and trilobites (trilo) in the Central Anti-Atlas (CAA), the Montagne Noire (MN), and the Cordillera Oriental (CO). Sobs and Sex were also calculated while separating between the Floian and the Tremadocian of the three regions (Supplementary Material 1). (b) DNCI analyses for trilobites and echinoderms during the Tremadocian (Trema) and Floian of the Central Anti-Atlas, the Montagne Noire, and the Cordillera Oriental.

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Buatois, Quantifying ecospace utilization and ecosystem engineering during the early Phanerozoic-The role of bioturbation and bioerosion. 2020, Pubmed