Fenestrate bryozoan fauna from the Middle Devonian of the Eifel (western Rhenish Massif, Germany)

Ernst, Andrej

doi:10.1007/s12549-022-00544-0

Cited by 3 publications

(2 citation statements)

References 22 publications

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“…36) presented various examples of mineralized inferred soft‐tissue remains in autozooecia of Mississippian fenestrate bryozoans. Ernst (2022 b ) illustrated similar structures in the Devonian fenestrate Rectifenestella aculeata (Sandberger & Sandberger, 1856). The usually singular rounded or cylindrical structures could remain in abandoned zooecia that are closed by terminal diaphragms.…”

Section: Discussionmentioning

confidence: 94%

Fossilized soft tissues in Palaeozoic bryozoans

Ernst

2023

Papers in Palaeontology

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Thin sections of three Palaeozoic bryozoans reveal fossilized soft tissues that show the position of organic cuticle and internal structures such as the membranous sac and gut. The fossilization occurred apparently due to fast burial under anoxic conditions. The position of a membranous sac in the Permian trepostome Rhombotrypella superangustata is indicative of a progressive polypide cycle. The position of the polypide in the Ordovician Graptodictya delicata behind the superior and interior hemisepta suggests a protective function of the hemisepta.

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Section: Discussionmentioning

confidence: 94%

Fossilized soft tissues in Palaeozoic bryozoans

Ernst

2023

Papers in Palaeontology

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“…Instead, it must have rested on the sediment convex (ventral) valve up or convex (ventral) valve down. Large flat strophomenoids are widely cited as examples of 'snowshoe morphology', animals that adapt to soft sediments by being broad and flat to avoid sinking in, as in the eponymous snow gear (Rhoads 1970;Bowen et al 1974;F€ ursich & Hurst 1974;Alexander 1975;Thayer 1975;Walker & Alberstadt 1975;McGhee 1976;Grant 1981;Kammer 1985;Hiller & Theron 1988;Baarli 1990;Holland & Patzkowsky 2007;Layou 2009;Ernst & Bohaty 2010;Smrecak & Brandt 2017;Brett et al 2020).…”

Section: The Life Position Debatementioning

confidence: 99%

Paradox lost: wide gape in the Ordovician brachiopod Rafinesquina explains how unattached filter‐feeding strophomenoids thrived on muddy substrates

Dattilo,

Freeman,

Hartshorn

et al. 2024

Palaeontology

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Strophomenoid brachiopods had thin, concavo‐convex shells, were ubiquitous colonizers of Palaeozoic muddy seafloors, and are hypothesized to have filter‐fed in a concave‐upward orientation. This orientation would elevate their line of commissure out of potentially lethal lophophore‐clogging mud. The paradox is that epibiont distributions on strophomenoids support a convex‐upward life position, as do studies of strophomenoid stability and trace fossils formed by strophomenoid sediment‐clearing. A premise of the concave‐upward orientation hypothesis is a narrow gape, which causes narrow, high velocity inhalant currents, leaving strophomenoids vulnerable to sediment entrainment. Herein we investigate the gape angle of Rafinesquina using serial thin sections and peels, silicified specimens, computer modelling, SEM analysis, x‐ray microCT, and 3D printing. Hinge line structure suggests that, conservatively, Rafinesquina could gape 40–45°. Such a gape occurred when diductor muscle contraction could not cause any further rotation, hinge teeth and crenulations were disengaged, and interareas interlocked. In contrast, when closed, hinge teeth were locked in hinge sockets. This wide gape eliminates constraints on feeding orientation. In either convex‐up or concave‐up orientation, Rafinesquina could feed with slow, diffuse inhalant currents incapable of disturbing sediment, and could snap valves shut to forcefully expel enough water to clear sediment from the mantle cavity, explaining previously described moat‐shaped trace fossils associated with shells. Our findings demonstrate that Rafinesquina gaped at an angle approximately equal to the angle between the two interareas when the valves are closed. Our analyses hint that other strophomenoids with similar interarea angles also lived with their shells widely agape.

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