Were all trilobites fully marine? Trilobite expansion into brackish water during the early Palaeozoic

Mángano, M. Gabriela; Buatois, Luís A.; Waisfeld, Beatriz G.; Muñoz, Diego F.; Vaccari, N. Emilio; Astini, Ricardo A.

doi:10.1098/rspb.2020.2263

Cited by 20 publications

(10 citation statements)

References 72 publications

(124 reference statements)

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“…Third, the occurrence of trace fossils in both mid fan delta and fan-delta toe deposits provides evidence of significant landward expansion of the Agronomic Revolution. This is consistent with several studies that have documented trace fossils in a wide variety of Cambrian marginal-marine environments, such as bays, deltas, and estuaries 23 , 24 , 56 , 59 – 64 . We note that fan deltas, given their coarse grain size, rapid deposition, and very high hydrodynamic energy, may be regarded as representing an end member in terms of stressor intensities if compared with other marginal-marine environments, such as interdistributary bays or estuarine basins.…”

Section: Discussionsupporting

confidence: 92%

Assessing the expansion of the Cambrian Agronomic Revolution into fan-delta environments

Ichaso

Buatois

Mángano

et al. 2022

Sci Rep

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The intensity, extent, and ecosystem-level impact of bioturbation (i.e. Agronomic Revolution) at the dawn of the Phanerozoic is a hotly debated issue. Middle Cambrian fan-delta deposits in southwestern Saskatchewan provide insights into the paleoenvironmental extent of the Agronomic Revolution into marginal-marine environments. The studied deposits reveal that several environmental stressors had direct impact on trace-fossil distribution and bioturbation intensities in Cambrian fan deltas. Basal and proximal subaerial deposits are characterized by very coarse grain size and absence of bioturbation. Mid-fan and fan-toe deposits were formed under subaqueous conditions and are characterized by rapid bioturbation events in between sedimentation episodes when environmental stressors were ameliorated, providing evidence of a significant landward expansion of the Agronomic Revolution. Transgressive marine deposits accumulated after the abandonment of the fan-delta system display high levels of bioturbation intensity, reflecting stable environmental conditions that favored endobenthic colonization. The presence of intense bioturbation in both subaqueous fan delta and transgressive deposits provides further support to the view that Cambrian levels of biogenic mixing were high, provided that stable environmental conditions were reached. Our study underscores the importance of evaluating sedimentary facies changes to assess the impact of environmental factors prior to making evolutionary inferences.

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Section: Discussionsupporting

confidence: 92%

Assessing the expansion of the Cambrian Agronomic Revolution into fan-delta environments

Ichaso

Buatois

Mángano

et al. 2022

Sci Rep

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“…This increase in the depth of trilobite penetration has been documented in members of the Cruziana rugosa group ( C . rugosa and C. furcifera , less for C. goldfussi ) during the Ordovician (Mángano et al, 2021; Stachacz et al, 2015). Deposit feeding arthropods and worms were the most influential bioturbators in deltaic sediments, resulting in intense disruption of microbial communities.…”

Section: Discussionmentioning

confidence: 99%

The interplay of environmental constraints and bioturbation on matground development along the marine depositional profile during the Ordovician Radiation

et al. 2021

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This study documents the distribution of matgrounds in a wide variety of environments recorded in the Ordovician Lashkerak and Ghelli Formations in the Alborz Mountains of northern Iran in order to evaluate controls on their distribution along the marine depositional profile. Detailed facies analysis allowed differentiating three groups of facies associations in the Lower to Upper Ordovician deposits of the Lashkerak formation: (i) estuarine system; (ii) wave‐dominated shoreface‐offshore complex; and (iii) mixed river‐ and wave‐influenced deltaic system. The Middle to Upper Ordovician deposits of the Ghelli formation are divided into two groups of facies associations: (i) tide‐influenced deltaic succession and (ii) deep‐water fan system. Microbially induced sedimentary structures (MISS) are present in deposits formed in the central estuarine basin (Lashkerak formation) and in proximal lobes and lobe fringes of deep–water turbidite fans (Ghelli formation). On the contrary, MISS are absent in deposits from the wave‐dominated shoreface‐offshore complex, river‐ and tide‐dominated deltas, and various subenvironments of the incised wave‐dominated estuary (i.e., bayhead delta and estuary mouth) and the deep‐marine turbidite fan system (i.e., turbidite channel, slope, and outer lobe). The lack of evidence of mat‐building microorganisms in the deltaic systems may have resulted from two factors: (1) high physico‐chemical stressors caused by river‐induced processes, and (2) increase in degree of sediment disturbance, biodiffusion, and bioirrigation by burrowing organisms. Formation of microbial mats in the wave‐dominated shoreface‐offshore complex was inhibited by the activity of an abundant and diverse infauna capable of reworking the sediment. Our analysis shows that the spatial distribution of microbial mats was controlled by an interplay of environmental factors and innovations in animal‐substrate interactions, mostly expressed by secular changes in bioturbation. This study supports the notion that the agronomic revolution was diachronic, with marginal‐marine and deep‐sea ecosystems lagging behind shallow‐marine settings.

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“…In active colonization, organisms exploit the benefits of a new environment, for example, a previously untapped food source and lack of competition. Estuaries provide conduits for active invasion that have been used by many organisms, notably fish and crustaceans, but also trilobites during the early Palaeozoic [ 53 ]. Alternatively, falling sea levels may lead to passive invasion by stranding organisms in water bodies that freshen over time.…”

Section: Discussionmentioning

confidence: 99%

Ostracods had colonized estuaries by the late Silurian

et al. 2021

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The fossil record of terrestrialization documents notable shifts in the environmental and physiological tolerances of many animal and plant groups. However, for certain significant components of modern freshwater and terrestrial environments, the transition out of marine settings remains largely unconstrained. Ostracod crustaceans occupy an exceptional range of modern aquatic environments and are invaluable palaeoenvironmental indicators in the fossil record. However, pre-Carboniferous records of supposed non-marine and marginal marine ostracods are sparse, and the timing of their marine to non-marine transition has proven elusive. Here, we reassess the early environmental history of ostracods in light of new assemblages from the late Silurian of Vietnam. Two, low diversity but distinct ostracod assemblages are associated with estuarine deposits. This occurrence is consistent with previous incidental reports of ostracods occupying marginal and brackish settings through the late Silurian and Devonian. Therefore, ostracods were pioneering the occupation of marginal marine and estuarine settings 60 Myr before the Carboniferous and they were a component of the early phase of transition from marine to non-marine environments.

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Were all trilobites fully marine? Trilobite expansion into brackish water during the early Palaeozoic

Cited by 20 publications

References 72 publications

Assessing the expansion of the Cambrian Agronomic Revolution into fan-delta environments

Assessing the expansion of the Cambrian Agronomic Revolution into fan-delta environments

The interplay of environmental constraints and bioturbation on matground development along the marine depositional profile during the Ordovician Radiation

Ostracods had colonized estuaries by the late Silurian

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