CONICET | Buscador de Institutos y Recursos Humanos

The new ichnotaxon Bromleyia magnifica n. igen., n. isp., attributed to the feeding activity ofbivalves, is proposed. This ichnotaxon consists of clusters of closely spaced curved ridges thatform a fan-shaped structure oppositely distributed on both sides of a longitudinal axis or,more rarely, being present only on one side. Intergradation between Protovirgularia, Lockeia,and Bromleyia forms a compound trace fossil that records the activity of a cleft-footprotobranch bivalve while burrowing, moving through the sediment, and stopping to depositfeed. A specimen from the Carboniferous of Arkansas, previously regarded as Lophocteniumisp., is here included in Bromleyia magnifica. The spreite in Lophoctenium reflects complexbehavioural patterns of horizontal strip-mining deposit feeders, including bundles of tubesbending to one side in a pectinate way or arranged on both sides in a highly systematicfashion, which contrasts with the coarse, horizontal fan-shaped, curved bundle of ridges fromthe Arkansas specimen. The trace fossil Hillichnus lobosensis records the activities of tellinaceandeposit feeders and displays feather-like spreite structures reminiscent of Bromleyia. However,the spreite in Hillichnus is more organized, recording repetitive probing through the sedimentin horizontal, oblique, and vertical directions of the tubular inhalant siphon. The resultingcomplex feeding structure, recorded in multiple preservational tiers, displays an alternatearrangement of ridges on either side of an axial basal structure. This configuration differsfrom the mostly horizontal, less-organized, coarse bundle of ridges with broadly oppositedistribution to the sides of an axis present in Bromleyia. Moreover, contrary to Hillichnus,Bromleyia is commonly associated with Lockeia, indicating significant differences in burrowingstrategy and mode of construction between these two ichnotaxa.

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