Tanyrhinichthys mcallisteri, a long-rostrumed Pennsylvanian ray-finned fish (Actinopterygii) and the simultaneous appearance of novel ecomorphologies in Late Palaeozoic fishes

Abstract

The Carboniferous radiation of fishes was marked by the convergent appearance of then-novel but now common ecomorphologies resulting from changes in the relative proportions of traits, including elongation of the front of the skull (rostrum). The earliest ray-finned fishes (Actinopterygii) with elongate rostra are poorly known, obscuring the earliest appearances of a now widespread feature in actinopterygians. We redescribe Tanyrhinichthys mcallisteri, a long-rostrumed actinopterygian from the Upper Pennsylvanian (Missourian) of the Kinney Brick Quarry, New Mexico. Tanyrhinichthys has a lengthened rostrum bearing a sensory canal, ventrally inserted paired fins, posteriorly placed median fins unequal in size and shape, and a heterocercal caudal fin. Tanyrhinichthys shares these features with sturgeons, but lacks chondrostean synapomorphies, indicating convergence on a bottom-feeding lifestyle. Elongate rostra evolved independently in two lineages of bottom-dwelling, freshwater actinopterygians in the Late Pennsylvanian of Euramerica, as well as in at least one North American chondrichthyan (Bandringa rayi). The near-simultaneous appearance of novel ecomorphologies among multiple, distantly related lineages of actinopterygians and chondrichthyans was common during the Carboniferous radiation of fishes. This may reflect global shifts in marine and freshwater ecosystems and environments during the Carboniferous favouring such ecomorphologies, or it may have been contingent on the plasticity of early actinopterygians and chondrichthyans.

The early diversification of ray‐finned fishes (Actinopterygii): hypotheses, challenges and future prospects

“…Actinopterygians are also being described from new British (Elliott, 2016 ) and Western European (Giles et al ., 2015 ; Štamberg & Steyer, 2021 ) deposits. By contrast, the majority of new species from North America stem from focussed efforts on well‐known localities, such as Bear Gulch (Lowney, 1980 ; Lund & Melton, 1982 ; Lund & Poplin, 1997 , 1999 ; Lund, 2000 ; Poplin & Lund, 2000 , 2002 ; Mickle et al ., 2009 ; Grogan & Lund, 2015 ), Kinney Brick Quarry (Gottfried, 1987 , 1992 ; Bardack, 1992 ; Zidek, 1992 ; Williams & Lucas, 2013 ; Stack et al ., 2021 ), and Mazon Creek (Bardack, 1979 ; Schultze & Bardack, 1987 ). Comparatively few taxa derive from more depauperate localities (Mickle, 2017 , 2018 ; Wilson, Pardo & Anderson, 2018 ).…”

The early diversification of ray-finned fishes (Actinopterygii): hypotheses, challenges and future prospects

“…6). Work remedying this is already underway using techniques such as CT-scanning (Giles et al, 2015;Pradel et al, 2016;Coates & Tietjen, 2018;Friedman et al, 2018;Figueroa et al, , 2021 and more traditional descriptive work (Choo, 2015;Štamberg, 2016;Mickle, , 2018Stack et al, 2020). In particular, CT-scanning will be critical in revealing internal anatomical details and increasing the number of phylogenetically informative characters beyond the dermal bones, which are often very similar among Palaeozoic actinopterygians .…”

The pharynx of the iconic stem-group chondrichthyanAcanthodes(Agassiz, 1833) revisited with micro computed tomography

“…Increasing the gape laterally may have been particularly important due to the anguilliform body shape of Acanthodes giving it a comparatively small head-on profile relative to its body size. In the ecological context of the late Palaeozoic Acanthodes is part of a wider trend towards the evolution of eel-like body shapes in a phylogenetically diverse range of fishes (Stack et al, 2020).…”

“…Recently a number of three-dimensionally preserved pharyngeal skeletons of Palaeozoic chondrichthyans have been described in great detail using computed tomographic (CT) methods, including other stem-group chondrichthyans (Coates et al, 2018;Dearden et al, 2019;Maisey et al, 2019) as well as Palaeozoic crown-group members (Pradel et al, 2014(Pradel et al, , 2021Coates et al, 2019Coates et al, , 2021Frey et al, 2019Frey et al, , 2020Hodnett et al, 2021;Klug et al, 2023), which show an unexpected range of feeding modes. However, Acanthodes remains important as one of the best preserved of these and is further interesting from a functional perspective as a very late-occurring acanthodian, seemingly adapted to be an anguilliform filter feeder, in the broader ecological context of the late Palaeozoic (Stack et al, 2020).…”