Fish and tetrapod communities across a marine to brackish salinity gradient in the Pennsylvanian (early Moscovian) Minto Formation of New Brunswick, Canada, and their palaeoecological and palaeogeographical implications

Abstract

42The cosmopolitan biogeography of many fish genera strongly indicates marine-based 43 dispersal, while strontium isotopic data suggest these same fish were exposed, at times, to ). An intriguing characteristic of this episode was the apparent widespread adoption of 68 a euryhaline habit amongst organisms as diverse as microconchids, ostracodes, xiphosurans 69 and fish (Anderson and Shuster 2003; Carpenter et al. 2011; Bennett et al. 2012; Gierlowski-70 Kordesch and Cassle 2015). Euryhaline animals are relatively rare in modern ecosystems 71 (Edwards and Marshall 2013; McCormick et al. 2013), and their dominance in Carboniferous 72 times suggests marine communities converged on similar osmoregulatory strategies in order 73 to utilise empty non-marine coastal ecospace for feeding and breeding (Williams et al. 2006; 74 Carpenter et al. 2014), prior to the widespread colonisation of freshwater tracts further inland. 75The mid-Carboniferous diversification event coincided with a sharp growth of 76Gondwanan ice sheets and the onset of significant Milankovitch-driven glacio-eustatic 86Much recent attention has been given to the apparent dominance of a euryhaline mode 87 of life amongst mid-Carboniferous fish communities (Schultze 2009; Carpenter et al. 2011 Carpenter et al. , 88 2014Carpenter et al. , 2015. However, consensus regarding ecology is currently lacking, with some 89 researchers arguing on palaeogeographic, sedimentological and geochemical grounds that fish 90 taxa, especially xenacanthid sharks (Masson and Rust 1984), may have been obligate 91 freshwater organisms (Śtamberg and Zajíc 2008;Fischer et al. 2011 Fischer et al. , 2013 Montañez and 92 Cecil 2013). In this paper, we describe a new fish fauna from the Carboniferous 93 (Pennsylvanian) of New Brunswick, Canada (Fig. 1A), and demonstrate -based on 94 independent indicators of palaeo-salinity -that fish taxa existed across a brackish to marine 95 gradient, and that communities must therefore have been euryhaline. We discuss how these 96 new findings improve understanding of Carboniferous fish ecology and the mid- 97Carboniferous diversification of non-marine ecosystems in particular. The fish fossils reported here were obtained from opencast mine sites (now reclaimed) within 102 the Minto Coalfield, Queens County, New Brunswick, Canada (Fig. 1A-C 98 +REVISE FOR TETRAPOD STORY 123Extensive borehole arrays indicate that this basal unconformity is marked by a major silcrete 124 paleosol, up to 9 m thick in places (Sullivan 1981; St Peter 2000), which mantles the 125 basement complex and indicates seasonally-dry climate weathering over the preceding (Fig. 3A), implying that the basin deepened towards the 137 southwest, and sediment progressively onlapped towards the northeast; and (2) NE-SW- Coal, fine towards the southwest (Fig. 3B) and suggest sediment transport in that direction. 140We note, however, that this inferred palaeoflow direction opposes regional patterns of Geological Surveys Branch, Fredericton (Fig. 4A). 154The low...

A fish and tetrapod fauna from Romer's Gap preserved in Scottish Tournaisian floodplain deposits

“…, ; Ó Gogáin et al . ). Early Carboniferous eurypterids are mostly restricted to brackish or freshwater environments (Braddy ; Lamsdell & Braddy ).…”

“…, ; Ó Gogáin et al . ). Common associations are Archichthys / Strepsodus and Screbinodus / Rhizodus , which has long had a confounding effect on the taxonomy of these genera (Andrews ; Jeffery ).…”

“…; Ó Gogáin et al . ); at least through the early part of the Late Carboniferous, the increasing taxonomic, morphological and ecological diversity of actinopterygians is considered to be largely a brackish and, in particular, marine phenomenon (Sallan & Coates , ). More abundant and morphologically diverse actinopterygians have been reported from Blue Beach, where the succession preserves multiple marine incursions (Mansky & Lucas ).…”

“…However, widespread euryhalinity among Devonian–Carboniferous vertebrates (Ó Gogáin et al . ; Goedert et al . ) may support the hypothesis of a cosmopolitan post‐extinction fauna in the Tournaisian (Friedman & Sallan ).…”

A Batrachichnus salamandroides trackway from the Minto Formation of central New Brunswick, Canada: implications for alternative trackmaker interpretations

“…Previous paleontological work on the Minto Formation is restricted to paleofloral assemblages documented by Bell (1962). A single trigonotarbid invertebrate body fossil (Miller and Forbes 2001) and a diverse faunal assemblage of aquatic vertebrates, which included undescribed tetrapod skeletal remains (Ó Gogáin et al 2016), represent the only known evidence of terrestrial biota from the Minto Formation of central New Brunswick. Prior to the present study, ichnofossils had not been documented from the Minto Formation.…”