Bromalites from the Upper Triassic Polzberg section (Austria); insights into trophic interactions and food chains of the Polzberg palaeobiota

Abstract

A rich assemblage of various types of bromalites from the lower Carnian “Konservat-Lagerstätte” from the Reingraben Shales in Polzberg (Northern Calcareous Alps, Lower Austria) is described for the first time in detail. They comprise large regurgitalites consisting of numerous entire shells of ammonoid Austrotrachyceras or their fragments and rare teuthid arm hooks, and buccal cartilage of Phragmoteuthis. Small coprolites composed mainly of fish remains were also found. The size, shape and co-occurrence with vertebrate skeletal remains imply that regurgitalites were likely produced by large durophagous fish (most likely by cartilaginous fish Acrodus). Coprolites, in turn, were likely produced by medium-sized piscivorous actinopterygians. Our findings are consistent with other lines of evidence suggesting that durophagous predation has been intense during the Triassic and that the so-called Mesozoic marine revolution has already started in the early Mesozoic.

The Upper Triassic Polzberg palaeobiota from a marine Konservat-Lagerstätte deposited during the Carnian Pluvial Episode in Austria

“…The basal part of the Reingraben Shales, directly above the Göstling Member (Fig. 2 ), appears with a finely, distinctly millimetre-laminated “Ildefonso type” interval (bright/dark stratification), without bioturbation 2 , 3 , 5 . The Reingraben Shales are approx.…”

“…The enormous amount and the quality of the varying fossil taxa enables special insights into the morphology of such otherwise rarely preserved fossil taxa. The Polzberg palaeobiota shows a nekton-dominated fauna with abundant fishes and cephalopods 5 . The main faunal elements (Figs.…”

“…minor 26 , 27 CLXXXVI = 186, p. 682). Constituents are ammonites 2 , 5 , 26 , 27 (n 4522), anaptychi 28 (n 46), coleoids 16 , 17 , 29 (proostraca, phragmocones, hooks, cartilage; n 386), bivalves 2 , 11 , 30 (n > 10.000), gastropods 30 (n 96), arthropods 3 , 18 , 30 (n 207), polychaetes (n 17), echinoderms 30 (n 1), trace fossils 5 (bromalites; n 112), conodontophorids (n 12), fish 5 , 11 , 14 , 31 – 33 (n 1181), chondrichtyes 2 , 5 (n 1); lungfish 12 , 13 , 34 , 35 (skull with attached teeth plates; n 1), coelocanths 13 , 36 , 37 (n 5) and rare plant remains (n 12; Table 1 ). A. minor appears with partly preserved buccal apparatuses of anaptychus-type lower jaws 28 .…”

“… 31 decapod lobster Obtusotelson summesbergeri Discosalaputium aschauerorum 18 Eustheria minuta 11 Polychaeta Palaeoaphrodite sp. 3 N Normal marine/benthic microphagous scavengers Historic mine tunnel and new locality Eunicidae indet 3 O Echinoidea Echinoidea indet 30 Normal marine/benthic grazing Historic mine tunnel and new locality Trace fossils coprolites 5 ; 3 Q Normal marine/benthic Historic mine tunnel and new locality regurgitalites 5 ; 3 P Vertebrata Actinopterygii Saurichthys calcaratus 2 , 5 , 14 ; 4 A Normal marine/nektic gregarious predatory carnivorous herbivorous Historic mine tunnel and new locality Polzbergia brochatus , Peltopleurus dirumptus 2 , 14 Nannolepis elegans , 14 , 4 B,C Habroichthys gregarius 2 …”

“…Palaeobiota of fossiliferous sites known as Konservat-Lagerstätte 1 (see also 2 , 3 ) are precious sources of palaeobiological information 4 . Such conservation Lagerstätten provide unique insights into palaeocommunities, food chains and dietary habits, as well as trophic interactions between the inhabitants of marine ecosystems 5 and references therein. New findings of additional fossil groups and the soft body preservation of numerous organisms shed light on such otherwise hidden Upper Triassic organisms.…”