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Fish and Tetrapod Communities Across a Marine to Brackish

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Fish and Tetrapod Communities Across a Marine to Brackish Palaeontology 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 palaeogeographic implications Journal: Palaeontology Manuscript ID PALA-06-16-3834-OA.R1 Manuscript Type: Original Article Date Submitted by the Author: 27-Jun-2016 Complete List of Authors: Ó Gogáin, Aodhán; Earth Sciences Falcon-Lang, Howard; Royal Holloway, University of London, Department of Earth Science Carpenter, David; University of Bristol, Earth Sciences Miller, Randall; New Brunswick Museum, Curator of Geology and Palaeontology Benton, Michael; Univeristy of Bristol, Earth Sciences Pufahl, Peir; Acadia University, Earth and Environmental Science Ruta, Marcello; University of Lincoln, Life Sciences; Davies, Thoams Hinds, Steven Stimson, Matthew Pennsylvanian, Fish communities, Salinity gradient, Euryhaline, Key words: Cosmopolitan, New Brunswick Palaeontology Page 1 of 121 Palaeontology 1 2 3 4 1 5 6 7 1 Fish and tetrapod communities across a marine to brackish salinity gradient in the 8 9 2 Pennsylvanian (early Moscovian) Minto Formation of New Brunswick, Canada, and 10 3 their palaeoecological and palaeogeographic al implications 11 12 4 13 14 5 by AODHÁN Ó GOGÁIN 1, 2 , HOWARD J. FALCON-LANG 3, DAVID K. CARPENTER 4, 15 16 6 RANDALL F. MILLER 5, MICHAEL J. BENTON 1, PEIR K. PUFAHL 6, MARCELLO 17 18 7 RUTA 7, THOMAS G. DAVIES 1, STEVEN J. HINDS 8 and MATTHEW R. STIMSON 5, 8 19 20 8 21 22 9 1 School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK; e-mails: 23 24 10 [email protected]; [email protected]; [email protected] 25 26 11 2 Current address: Department of Geology, Trinity College Dublin, Dublin 2, Ireland 27 3 28 12 Department of Earth Sciences, Royal Holloway, Egham, Surrey, TW20 0EX, UK; e-mail: 29 30 13 [email protected] 31 4 32 14 Ocean and Earth Science, National Oceanography Centre Southampton, University of 33 34 15 Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH, UK; e-mail: 35 [email protected] 36 16 37 17 5 Natural Science Department, New Brunswick Museum, 277 Douglas Avenue, Saint John, 38 39 18 New Brunswick, E2K 1E5, Canada; e-mails: [email protected], 40 41 19 [email protected] 42 43 20 6 Department of Earth and Environmental Science, Acadia University, Wolfville, Nova Scotia, 44 45 21 B4P 2R6, Canada; e-mail: [email protected] 46 47 22 7 School of Life Sciences, University of Lincoln, Green Lane, Lincoln, LN6 7DL, UK; e- 48 49 23 mail: [email protected] 50 51 24 8 New Brunswick Department of Energy and Mines, Geological Surveys Branch, Fredericton, 52 53 25 New Brunswick, E3B 5H1, Canada; e-mail: [email protected] 54 55 56 57 58 59 60 Palaeontology Palaeontology Page 2 of 121 1 2 3 4 2 5 6 7 26 Abstract: Euryhaline adaptations in Pennsylvanian vertebrates allowed them to inhabit the 8 marine to freshwater spectrum. This is illustrated by new assemblages of fish and tetrapods 9 27 10 28 from the early Moscovian Minto Formation of New Brunswick, Canada. Fish include 11 12 29 chondrichthyans (xenacanthids , and the enigmatic Ageleodus ), acanthodians (gyracanthids and 13 14 30 acanthodiforms), sarcopterygians (rhizodontids, megalichthyids and dipnoans), and 15 16 31 actinopterygians (eurynotiforms). Tetrapods include small small- to medium-sized, and 17 18 32 largely aquatic, stem tetrapods (colosteids) and anthracosaurs (embolomeres). A key finding is 19 20 33 that the parautochthonous fossil assemblages are preserved across a salinity gradient, with 21 22 34 diversity (measured by the Simpson Index) declining from open marine environments, 23 24 35 through brackish embayments, and reaching a nadir in tidal estuaries. Chondrichthyans 25 26 36 dominate the entire salinity spectrum (65% of fossils), a distribution that demonstrates a 27 28 37 euryhaline mode of life, and one large predatory chondrichthyan, Orthacanthus , may have 29 30 38 practised filial cannibalism in coastal nurseries because its heteropolar coprolites contain 31 32 39 juvenile xenacanthid teeth. In contrast, other fish communities were more common in open 33 34 40 marine settings while tetrapods were more common in coastal brackish waters. While all these 35 faunas were , also , likely , euryhaline, their osmoregulation was, perhaps, less versatile. The 36 41 37 42 demonstration of widespread euryhalinity among fish and aquatic tetrapods explains why 38 39 43 Pennsylvanian faunas generally show a cosmopolitan biogeography because taxa were able to 40 41 44 disperse via seaways. It also resolves the paradox of enriched strontium isotopic signatures 42 43 45 observed in these faunas because organisms would have been, at times, exposed to continental 44 45 46 water bodies as well. Therefore, our new findings contribute to the long-running debates about 46 47 47 the ecology of Pennsylvanian fishes and tetrapods. 48 49 48 Key words: Pennsylvanian, fish communities, salinity gradient, euryhaline, cosmopolitan, 50 51 49 New Brunswick. 52 53 54 55 56 57 58 59 60 Palaeontology Page 3 of 121 Palaeontology 1 2 3 4 3 5 6 7 50 EURYHALINE animals are relatively rare in modern ecosystems (Edwards and Marshall 8 2013; McCormick et al. 2013), with less than 10% of organisms adopting this osmoregulatory 9 51 10 52 strategy (Schultz and McCormick 2013). In contrast, euryhaline adaptations appear to have 11 12 53 been much more widespread at certain times in the geologic al past (Minter et al. 2016), and, 13 14 54 in fact, may have played a critical transitional role in the Palaeozoic colonisation of 15 16 55 continental freshwater ecospace (Buatois et al. 1998; Miller and Labandeira 2002; Park and 17 18 56 Gierlowski-Kordesch 2007; Falcon-Lang et al. 2015 a). Adaptation to lower and more 19 20 57 variably saline (brackish to fresh) water bodies commenced as early as the Ordovician 21 22 58 (MacNaughton et al. 2002; Davies and Sansom 2009; Sansom et al. 2009), and the abundance 23 24 59 and complexity of these ecosystems steadily increasing increased through the Silurian– 25 26 60 Carboniferous (Jones and Dixon 1977; Buatois et al. 2005; Kennedy et al. 2012). 27 28 61 Colonisation patterns closely parallel the Ordovician rise of hepatophytes and the Silurian– 29 30 62 Carboniferous diversification of tracheophytes (Gensel and Edwards 2001), indicating co- 31 32 63 evolutionary teleconnections between land plants, terrestrial-marine nutrient export patterns 33 34 64 (Algeo and Scheckler 1998), and the carrying capacity of ‘non-marine’ coastal environments 35 (Prescott et al. 2014). 36 65 37 66 Adoption of euryhalinity appears to have peaked during a “mid-Carboniferous 38 39 67 diversification” when this mode of life, temporarily, became dominant (Davies and Gibling 40 41 68 2013; Falcon-Lang et al. 2015 a) among organisms as diverse as microconchids, ostracodes, 42 43 69 xiphosurans and fish (Anderson and Shuster 2003; Carpenter et al. 2011; Bennett et al. 2012; 44 45 70 Gierlowski-Kordesch and Cassle 2015; Gierlowski-Kordesch et al. 2016), perhaps, in order , 46 47 71 perhaps, to utilise depauperate non-marine coastal ecospace for feeding and breeding 48 49 72 (Williams et al. 2006; Carpenter et al. 2014). Rapid diversification coincided with the sharp 50 51 73 growth of Gondwanan ice sheets and the onset of significant Milankovitch-driven glacio- 52 53 74 eustatic fluctuations (Fielding et al. 2008; Montañez and Poulsen 2013). These marine 54 55 56 57 58 59 60 Palaeontology Palaeontology Page 4 of 121 1 2 3 4 4 5 6 7 75 transgressions , with magnitudes up to 120 m (Rygel et al. 2008) , repeatedly flooded 8 continental margins, creating extensive epicontinental microtidal seaways (Wells et al. 2005), 9 76 10 77 whose salinity slowly decreased in a landward direction over many hundreds of kilometres 11 12 78 (Falcon-Lang 2005; Falcon-Lang et al. 2015 b), similar to the present-day Baltic Sea 13 14 79 (Andersson et al. 1992 1994). This palaeo-oceanographic context probably provided optimum 15 16 80 conditions for euryhaline organisms to exploit brackish environments. 17 18 81 In this paper, we describe euryhalinity in Late Pal aeozoic vertebrate communities. 19 20 82 Facies analysis suggests that a wide range of fish, including gyracanthids, elasmobranchs, 21 22 83 dipnoans, rhizodonts and megalichthyids, as well as tetrapods, existed in freshwater to 23 24 84 brackish environments in Devonian–Carboniferous times (Friedman and Sallan 2012; 25 26 85 Schultze 2013), and much recent attention has been given to the apparent dominance of a 27 28 86 euryhaline mode of life among mid-Carboniferous vertebrate communities (Schultze 2009; 29 30 87 Carpenter et al. 2011, 2014, 2015). However, consensus regarding ecology is currently 31 32 88 lacking, with some researchers arguing on palaeogeographic al , sedimentological and 33 34 89 geochemical grounds that fish taxa, especially xenacanthid sharks (Masson and Rust 1984) , 35 and tetrapods, may have been obligate freshwater organisms (Johnson, 1979, 1999; Śtamberg 36 90 37 91 and Zajíc 2008; Fischer et al. 2011, 2013; Montañez and Cecil 2013). In this paper, we 38 39 92 describe a new fauna of fish and tetrapods from the Carboniferous (Pennsylvanian; early 40 41 93 Moscovian) of New Brunswick, Canada (Fig. 1A), and demonstrate – based on independent 42 43 94 indicators of palaeo-salinity – that certain fish and tetrapod taxa existed across a brackish to 44 45 95 marine gradient, and that communities must therefore have been euryhaline. We discuss how 46 47 96 these new findings improve understanding of Carboniferous fish and tetrapod ecology. 48 49 97 50 51 98 GEOLOGICAL CONTEXT 52 53 54 55 56 57 58 59 60 Palaeontology Page 5 of 121 Palaeontology 1 2 3 4 5 5 6 7 99 The fish and tetrapod fossils reported here were obtained from opencast mine sites (now 8 reclaimed) within the Minto Coalfield, Queens County, New Brunswick, Canada (Fig.
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