Taphonomic history and trophic interactions of an ammonoid fauna from the Upper Triassic Polzberg palaeobiota

Abstract

The taphonomic mechanisms of a mono- to pauci-specific ammonoid fauna comprising 3565 specimens from the lower Carnian Polzberg Konservat-Lagerstätte near Lunz am See (Northern Calcareous Alps, Lower Austria) is described. The fossiliferous layers were deposited during the Julian 2 Ib (Austrotrachyceras austriacum Zone, Austrotrachyceras minor biohorizon). The deposits comprise abundant nektic ammonoids of the trachyceratid genus Austrotrachyceras. The bivalve Halobia, dominant among the invertebrates, is followed in abundance by the ammonoids Austrotrachyceras and Paratrachyceras, the coleoid Phragmoteuthis and frequent vertebrate actinopterygian fish. The monotonous ammonoid assemblage comprises abundant Austrotrachyceras, frequent Paratrachyceras, rare Carnites and Simonyceras. Recently collected ammonoids were sampled bed-by-bed and compared to extensive historical collections from the same localities. Bromalites (coprolites and regurgitalites) produced by large durophagous fish comprise ammonoid and fish masses and accompany the ammonoid-dominated Polzberg palaeobiota. The ammonoid fauna here presents a window into the nektic cephalopod world of the Upper Triassic assemblage and palaeoenvironment during the deposition of the fossiliferous layers. The frequent occurrence of the vertically oriented (external side horizontal to bedding plane) ammonoid shell fragments hint at a deposition after lethal fish or coleoid attacks. The Polzberg ammonoids were deposited under calm and dysoxic conditions in fine-laminated marlstones and shales of the lower Carnian Polzberg Sub-Basin within the Polzberg Konservat-Lagerstätte.

Morphology, taxonomy and trophic interactions of rostrum-less coleoids from the Late Triassic Polzberg Konservat-Lagerstätte (Lower Austria)

“…The material derives from the Reingraben shales of the late Triassic (Julian II, Carnian) Konservat-Lagerstätte Polzberg (Fig. 1; GPS N 47° 53′ 5.90″ and E 15° 4′ 27.70″) (Lukeneder & Lukeneder, 2021, 2022a, 2022bLukeneder et al, 2020) at 712 m above sea level, which was first discovered by Stur (1874). The site is located about 4.5 km northeast of Lunz am See within the Polzberg Basin.…”

“…Krystyn (1998) proposed a basinal environment, cut-off from open marine conditions (see also Doguzhaeva et al, 2007b). More recent interpretations point to a deep marine environment with mainly nektic faunal elements (Lukeneder & Lukeneder, 2021, 2022a. Since this environment largely lacked infaunal elements and often even benthic fauna, the oxygen levels are proposed to have been dysoxic or even anoxic (Forchielli & Pervesler, 2013;Lukeneder & Lukeneder, 2021).…”

“…1) has yielded many belemnoid hard tissues including phragmocones, proostraca, cephalic cartilages and arm hooks (Doguzhaeva & Summesberger, 2012;Doguzhaeva et al, 2006Doguzhaeva et al, , 2007bLukeneder & Lukeneder, 2022b;Mojsisovics von Mojsvar, 1882;Suess, 1865). Soft tissues from ammonoids and belemnoids have also been reported (Doguzhaeva et al, 2007a;Lukeneder & Lukeneder, 2022a). However, much of the coleoid fauna is based on isolated, exceptionally preserved historical specimens, which do not reflect the entire faunal assemblage.…”

Multi-proxy record of the Austrian Upper Triassic Polzberg Konservat-Lagerstätte in light of the Carnian Pluvial Episode

“…The Upper Triassic Polzberg section in Austria (Fig. 1 ) comprises a unique Konservat-Lagerstätte 18 , 19 and is one of the best reference sections for the CPE in Austria and in the world because the biostratigraphy and taxonomy, taphonomy and trophic relations of various marine organisms of the Reifling Basin 4 , 20 , 21 are well studied. This section therefore represents a key section for the lower Carnian Konservat-Lagerstätte worldwide, making it an Upper Triassic high-quality depositional archive of marine ecosystems for this period.…”

“…The Carnian paleobiota from the Polzberg Konservat-Lagerstätte 4 , 22 , 23 has been historically and recently studied for several topics, yielding results on the paleoenvironment and trophic chain 4 , 24 as well as on the taxonomy and taphonomy of ammonoids 20 , 25 , including belemnoid cartilage investigations 21 .…”