Temporal dynamics of encrusting communities during the Late Devonian: a case study from the Central Devonian Field, Russia

Abstract

In this study we focused on the dynamics of encrusting assemblages preserved on brachiopod hosts collected from upper Frasnian and lower Famennian deposits of the Central Devonian Field, Russia. Because the encrusted brachiopods come from deposits bracketing the Frasnian/Famennian (F/F) boundary, the results also shed some light on ecological differences in encrusting communities before and after the Frasnian–Famennian (F-F) event. To explore the diversity dynamics of encrusting assemblages, we analyzed more than 1300 brachiopod valves (substrates) from two localities. Taxon accumulation plots and shareholder quorum subsampling (SQS) routines indicated that a reasonably small sample of brachiopod host valves (n=50) is sufficient to capture the majority of the encrusting genera recorded at a given site. The richness of encrusters per substrate declined simultaneously with the number of encrusting taxa in the lower Famennian, accompanied by a decrease in epibiont abundance, with a comparable decrease in mean encrustation intensity (percentage of bioclasts encrusted by one or more epibionts). Epibiont abundance and occupancy roughly mirror each other. Strikingly, few ecological characteristics are correlated with substrate size, possibly reflecting random settlement of larvae. Evenness, which is negatively correlated with substrate size, shows greater within-stage variability among samples than between Frasnian and Famennian intervals and may indicate the instability of early Famennian biocenoses following the faunal turnover. The occurrence distribution of encrusters points to nonrandom associations and exclusions among several encrusting taxa. However, abundance and occupancy of microconchids remained relatively stable throughout the sampled time interval. The notable decline in abundance (~60%) and relatively minor decline in diversity (~30%) suggest jointly that encrusting communities experienced ecological collapse rather than a major mass extinction event. The differences between the upper Frasnian and lower Famennian encrusting assemblages may thus record a turnover associated with the F-F event.

Enigmatic encrusting fossils from the Upper Devonian of Russia: probable Rothpletzella microproblematica preserved in three dimensions

“…The deposits of the Main Devonian Field and Central Devonian Field areas in Russia are well known for their rich fossil content and diverse hard substrates hosting rich encrusting assemblages, including fossils of uncertain affinities listed above (Hecker 1983;Zatoń and Krawczyński 2011;Zatoń et al 2017). Careful examination of brachiopod shells from the Upper Devonian of the Central Devonian Field, however, revealed the presence of intriguing, fan-shaped encrusters which have not been previously reported.…”

“…The deposits at Khlevnoe and Krivobor'e are dominated by brachiopods and are rich in gastropods, tabulate and rugose corals, as well as various encrusting taxa. The encrusted brachiopod fauna is represented mainly by spiriferids (Cyrtospirifer, Theodossia), atrypids (Variatrypa) and productids (Donalosia), as well as subordinate orthotetids (Schuchertella) (Sokiran 2002;Zatoń and Krawczyński 2011;Zatoń et al 2017).…”

“…During the Devonian, encrusting organisms were very common due to the presence of a variety of suitable substrates, especially in the form of abundant and diverse corals and brachiopods (e.g., Alvarez and Taylor 1987;Baird and Brett 1983;Bordeaux and Brett 1990;Zapalski 2005;Schneider 2013;Zatoń et al 2015Zatoń et al , 2017Zatoń et al , 2018, as well as lithic hardgrounds and cobbles (e.g., Baird 1976Baird , 1981Zatoń et al 2014). Compared with Mesozoic encrusting communities, those in the Palaeozoic, exemplified by Devonian assemblages, differed much in their taxonomic composition.…”

Palaeoecological analysis of a sclerobiont fauna on a single basibiont across the Valanginian of the Neuquén Basin, west-central Argentina

“…In addition, studies are beginning to analyse changes of sclerobiofacies across specific events or time periods (Schneider ; Zatoń et al . ), which requires sampling within a single facies to avoid mixing of different habitats (Patzkowsky & Holland ).…”

“…Therefore, more data are required on how sclerobiont communities vary according to independently defined parameters, and this is especially true for the Mesozoic (Brett et al 2012). In addition, studies are beginning to analyse changes of sclerobiofacies across specific events or time periods (Schneider 2013;Zato n et al 2017), which requires sampling within a single facies to avoid mixing of different habitats (Patzkowsky & Holland 2012).…”