Numerical analyses of selected microencrusters from the Cipit boulders of the St Cassian Formation (Dolomites, NE Italy): palaeoecological implications

Abstract

The ecological relationships among six microencruster species from the Cipit boulders of the St Cassian Formation (Ladinian–Carnian of the Dolomites, NE Italy) were studied in detail. 112 thin sections in postcard format (10 × 15 cm) and in 7.5 × 10 cm from the localities Alpe di Specie and Misurina were taken into account. Initially, twelve microencruster species were found: Koskinobullina socialis, Terebella lapilloides, Tubiphytes obscurus, Baccanella floriformis, Reptonoditrypa cautica, Plexoramea cerebriformis, Ladinella porata, Microtubus communis, Pseudorothpletzella schmidi, Alpinophragmium perforatum, Planiinvoluta sp and Tethysocarnia cautica. A phenetic algorithm combining three cluster analyses in R‐mode (UPGMA, WPGMA and nearest neighbour) as well as two indices (Jaccard and Bray–Curtis) was performed on all samples. Six microencruster species – grouped in three pairs – were found to have high Jaccard and low Bray–Curtis values at all algorithms. These pairs are represented by Koskinobullina socialis – Pseudorothpletzella schmidi, Terebella lapilloides – Tubiphytes obscurus and Reptonoditrypa cautica – Baccanella floriformis, and were clearly recognizable as robust branches in all phenograms. A further index (Simpson's similarity index) was included successfully in the algorithm in order to sustain the robustness of these phena. This method proved to render reliable results and could be successfully applied in all reef and reef‐like fossil ‘communities’, with the aim of establishing the palaeoecological implications and the specific constraints of selected microencrusters.

Facies Associations and Microfossils From the Middle-Upper Triassic Limestones of the Transilvanian Nappes (Perșani Mountains, Eastern Carpathians, Romania)

“…Microproblematic encrusting organisms are well known for their role in stabilising reefal bioconstructions (Reitner, 2013). Baccanella floriformis prefers high-energy shallow conditions (Martini et al, 2004;Sanchez-Beristain, 2010;Sanchez-Beristain & Reitner, 2018). This microproblematic organism is frequently associated with bioconstructions or rudstone deposits.…”

From fossil associations to ecological communities: a case study from the ‘Cipit boulders’ of the upper Ladinian–lower Carnian St Cassian Formation, Dolomites, NE Italy

“…Micro‐encrusters were crucial in the determination of fossil associations, due to their excellent preservation, abundance and diversity. In a recent study by the authors of this work (Sánchez‐Beristain & Reitner 2019a), ecological interactions even between micro‐encrusters could be determined with aid of this method.…”

“…Wendt 1982; Reitner 1987; Keupp et al . 1989; Sánchez‐Beristain & Reitner 2012, 2016, 2018, 2019a,b), thus posing a problem for the definition of fossil ecological communities at the St Cassian Formation. Furthermore, working with olistoliths would mean a constraining factor for a feasible palaeoenvironmental analysis, since only incomplete (‘winnowed’) communities (Fagerstrom 1964, p. 1201) or even organisms would be recovered.…”

“…Schmid 1996; Reolid et al . 2009; Sánchez‐Beristain & Reitner 2012, 2019a). These organisms usually do not exceed 5 mm in size (Schmid 1996; Sánchez‐Beristain & Reitner 2012) and comprise a wide taxonomic diversity which includes bacteria (Saint Martin 2010), protozoans (Schmid 1996), algae (Shiraishi & Kano 2004; Schlagintweit & Gawlick 2008), fungi (Mello 1977), bryozoans (Reolid et al .…”

“…Leinfelder et al . 1993; Schmid 1996; Sánchez‐Beristain & Reitner 2012, 2019a). This can be extremely helpful while assessing palaeoecological features of associated reef building organisms.…”