A highly diverse bivalve fauna from a Bithynian (Anisian, Middle Triassic) Tubiphytes‐microbial buildup in North Dobrogea (Romania)

Abstract

This paper describes a rich bivalve fauna from the Tubiphytes-Limestone Member (Bithynian, early middle Anisian) of the Caerace Formation in North Dobrogea (Romania). We report 51 bivalve species, including 7 new species and 2 new genera: Atrina multicostata sp. nov., Pinna simionescui sp. nov., Chlamys (Praechlamys) prima sp. nov., Entolium reticulatum sp. nov., Scythentolium anisicum sp. nov., Romaniamya mahmudiaensis gen. et sp. nov. and Praedicerocardium vetulus gen. et sp. nov. The latter taxon represents the oldest Triassic megalodontoid. We provide detailed descriptions of the bivalve fauna, discuss the ecology and compare species richness in the Early and Middle Triassic, showing that the bivalve assemblage of North Dobrogea is much more diverse than all previously described Early Triassic bivalve faunas, but not as rich as several faunas from the late Anisian and Ladinian. The relative richness of the Dobrogea fauna with respect to geologically older and younger faunas suggests that it represents an early stage of the main rediversification of bivalves after the end-Permian mass extinction.

Dynamics of the Largest Carbon Isotope Excursion During the Early Triassic Biotic Recovery

“…The low competition within the shelly benthos most likely contributed to this delay (Hautmann et al, 2015). Diversified bivalve communities returned in the middle Anisian (Friesenbichler et al, 2019) while coral reefs diversity was not restored to levels equivalent to that of the late Permian diversity until the Ladinian (Stanley, 2003), i.e., about 6 Myr after resumption of a stable carbon cycle. Of paramount importance is to reconstruct the relative timing of the global excursion of the carbon cycle, of successive diversification-extinction cycles of the nekton, intercalated ecological swaps of land plants punctuated by fern spikes, of eustatic sea-level change, carbonate crises and deposition of black shales dominated by terrestrial organic matter (OM) on shelves, and of climate change.…”

New Triassic Aviculopectinoidea (Bivalvia), with notes on the taxonomic concept of the superfamily

“…The fossils were associated with a Tubiphytes -microbial buildup within the Caerace Formation, located in the northeastern part of the quarry. Further details on the fossil locality, stratigraphy, and environmental context are given in Friesenbichler et al (2019).…”

“…Chlamys volaris ; Zardini, pl. 18, figs 8a, b.2019‘ Pecten ’ volaris ; Friesenbichler et al, p. 12, fig. 4H.…”

“…See Friesenbichler et al (2019). We add here that this species is probably equiconvex, based on our material and the figures in Allasinaz (1972, pl.…”

“…The Triassic was a time of major evolutionary transitions in bivalves, which occurred at least partly in response to increased ecological opportunities after the end-Permian mass extinction (Gould and Calloway, 1980; Hautmann, 2007; Ros et al, 2011; Friesenbichler et al, 2019). Some of the most species-rich extant bivalve taxa have their roots in that time, such as the oysters (Hautmann, 2001; Hautmann et al, 2017) and the scallops (Hautmann, 2010).…”