Data from: 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

Euryhaline adaptations in Pennsylvanian vertebrates allowed them to inhabit the marine to freshwater spectrum. This is illustrated by new assemblages of fish and tetrapods from the early Moscovian Minto Formation of New Brunswick, Canada. Fish include chondrichthyans (xenacanthids and the enigmatic Ageleodus), acanthodians (gyracanthids and acanthodiforms), sarcopterygians (rhizodontids, megalichthyids and dipnoans), and actinopterygians (eurynotiforms). Tetrapods include small- to medium-sized, and largely aquatic, stem tetrapods (colosteids) and anthracosaurs (embolomeres). A key finding is that the parautochthonous fossil assemblages are preserved across a salinity gradient, with diversity (measured by the Simpson Index) declining from open marine environments, through brackish embayments, and reaching a nadir in tidal estuaries. Chondrichthyans dominate the entire salinity spectrum (65% of fossils), a distribution that demonstrates a euryhaline mode of life, and one large predatory chondrichthyan, Orthacanthus, may have practised filial cannibalism in coastal nurseries because its heteropolar coprolites contain juvenile xenacanthid teeth. In contrast, other fish communities were more common in open marine settings while tetrapods were more common in coastal brackish waters. While all these faunas were also likely to have been euryhaline, their osmoregulation was, perhaps, less versatile. The demonstration of widespread euryhalinity among fish and aquatic tetrapods explains why Pennsylvanian faunas generally show a cosmopolitan biogeography because taxa were able to disperse via seaways. It also resolves the paradox of enriched strontium isotopic signatures observed in these faunas because organisms would have been, at times, exposed to continental water bodies as well. Therefore, our new findings contribute to the long-running debate about the ecology of Pennsylvanian fishes and tetrapods.

宾夕法尼亚纪（Pennsylvanian）脊椎动物的广盐适应（euryhaline adaptations）使其能够栖息于从海水到淡水的完整生境梯度中。这一结论可通过加拿大新不伦瑞克省莫斯科阶（Moscovian）早期明顿组（Minto Formation）新发现的鱼类与四足类化石组合得到佐证。本次发现的鱼类类群包括：软骨鱼类（chondrichthyans）——异棘鲨科（xenacanthids）与神秘的阿吉莱杜斯鲨属（Ageleodus）；棘鱼类（acanthodians）——旋棘鱼科（gyracanthids）与棘鱼形目（acanthodiforms）；肉鳍鱼类（sarcopterygians）——根齿鱼科（rhizodontids）、巨孔鱼科（megalichthyids）与肺鱼类（dipnoans）；以及辐鳍鱼类（actinopterygians）——宽颌鱼形目（eurynotiforms）。四足类类群则包括中小型且主要水生的茎四足类（stem tetrapods）中的壳鱼科（colosteids），以及炭螈类（anthracosaurs）中的栓塞螈目（embolomeres）。
本研究的关键发现在于：准原地化石组合（parautochthonous fossil assemblages）沿盐度梯度保存，辛普森多样性指数（Simpson Index）从开阔海洋环境、经咸水海湾，至潮汐河口（tidal estuaries）逐渐降低，并在潮汐河口达到最低点（nadir）。软骨鱼类在整个盐度梯度生境中占主导地位（占化石总量的65%），这一分布模式证实其具备广盐性生活模式；其中一类大型掠食性软骨鱼类——直棘鲨属（Orthacanthus），可能曾在沿岸育幼场实施亲子相食（filial cannibalism），因其异极性粪化石（heteropolar coprolites）中检出幼异棘鲨的牙齿。
与之形成对比的是，其他鱼类群落在开阔海洋环境中更为常见，而四足类则更多栖息于沿岸咸水水域。尽管这些类群大概率也具备广盐适应性，但其渗透压调节（osmoregulation）能力或许稍显不足。
本次研究证实了鱼类与水生四足类中广泛存在的广盐适应性，这解释了为何宾夕法尼亚纪动物群整体呈现世界性生物地理分布（cosmopolitan biogeography）——各类群可通过海道完成扩散。同时，这也解决了此前在这些动物群中观测到的锶同位素特征（strontium isotopic signatures）富集悖论：生物有时也会接触大陆水体。因此，本研究的新发现为长期以来关于宾夕法尼亚纪鱼类与四足类生态的学术争论提供了重要新证据。