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Coexistence of algae and a graptolite-like problematicum: a case study from the late Silurian of Podolia (Ukraine)

Skompski Stanisław, Kozłowski Wojciech, Łuczyński Piotr, Kozłowska Anna

Acta Geologica Polonica

2023

Vol. 73, no. 2

115--133

This contribution presents the record of an abundant assemblage of well-preserved, thallophytic noncalcified algae and of an epibiotic form that has been recognised as a putative graptolite from the upper Silurian (Ludlow, Gorstian–Ludfordian) of Podolia (western part of Ukraine). The sediments represent a shallow peritidal zone of the shelf. A new genus and species, Voronocladus dryganti, belonging to the Dasycladales Pascher, 1931, is established. Most of the specimens representing the algal thallus are overgrown by problematical epibiotic graptolites, described as Podoliagraptus algaeoides gen. et sp. nov. This phenomenon is explained as an epiphytic mode of life of the putative graptolite on algae, and is herein compared to recently known coexistences of algae with other organisms. The excellent state of preservation, and the abundance of studied Dasycladales algae and epibiotic problematics indicate that the investigated mudstone layer can be treated as a ‘Konservat Lagerstätte’ sensu Seilacher (1970).

The ecological significance of solitary coral and bivalve epibionts on Lower Cretaceous (Valangianian-Aptian) ammonoids from the Italian Dolomites

Lukeneder A.

Acta Geologica Polonica

2008

Vol. 58, no. 4

425-436

Lower Cretaceous deposits of the Puez section in the Dolomites (northern Italy) yielded a rich ammonoid fauna (28 genera, n = 424) showing unique epifaunal encrustations by the ahermatypic solitary scleractinian ?Cycloseris LAMARCK, 1801. The coral encrusted only the outer shell surfaces of the ammonoids; the inner surface remained unaffected. Such a Cretaceous community and the relationship between the two fossil groups are described for the first time. The shells of dead ammonoids sank to the sea bottom and became colonized by the coral larvae, as documented by the location of the epibionts on only one side of the shells. The coral was fixed to the ammonoid shell for its entire life. Only the "sediment free" upper side of the ammonoid shells could be inhabited by epibionts such as corals and serpulids. The encrustation of ammonoid shells by the bivalve Placunopsis represents a different situation in that both sides of the ammonoid shells were affected, pointing to encrustation of floating ammonoids. This long-term infestation in the water column contrasts with coral settlement on the sea-floor. Ammonoid specimens encrusted by Placunopsis never exhibit encrustation by corals. The ammonoid-coral relationship from the Dolomites is documented from the Valanginian to Aptian interval. Examples of coral epibionts on ammonoids and other fossil groups throughout the geological column are briefly reviewed.