A Permian fish reveals widespread distribution of neopterygian-like jaw suspension

Abstract

The actinopterygian crown group (comprising all living ray-finned fishes) originated by the end of the Carboniferous. However, most late Paleozoic taxa are stem actinopterygians, and broadly resemble stratigraphically older taxa. The early Permian †Brachydegma caelatum is notable for its three-dimensional preservation and past phylogenetic interpretations as a nested member of the neopterygian crown. Here, we use computed microtomography to redescribe †Brachydegma, uncovering an unanticipated combination of primitive (e.g., aortic canal; immobile maxilla) and derived (e.g., differentiated occipital ossifications; posterior stem of parasphenoid; two accessory hyoidean ossifications; double jaw joint) dermal and endoskeletal features relative to most other Paleozoic actinopterygians. Some of these features were previously thought to be restricted to the neopterygian crown. The precise phylogenetic position of †Brachydegma is unclear, with placements either on the polypterid stem, or as an early-diverging stem neopterygian. However, our analyses decisively reject previous placements of †Brachydegma in the neopterygian crown. Critically, we demonstrate that key-endoskeletal components of the hyoid portion of the suspensorium of crown neopterygians appeared deeper in the tree than previously thought.

Large durophagous fish from the Spathian (late Early Triassic) of Romania hints at earlier onset of the Triassic actinopterygian revolution

“…To date, the anatomy of the palate and its relationship to neighbouring bones (e.g. maxilla) is reliably known only in a small sample of three-dimensionally preserved Palaeozoic and early Mesozoic actinopterygian fossils, such as †Australosomus, †Birgeria, †Boreosomus, †Brachydegma, †Fukangichthys, †Mimipiscis, †Moythomasia, †Pteronisculus (= †'Glaucolepis ' Stensi€ o, 1921), †Raynerius, †Saurichthys and †Watsonulus (Stensi€ o 1925(Stensi€ o , 1932Nielsen 1942Nielsen , 1949Gardiner 1984;Olsen 1984;V eran 1996;Giles et al 2015Giles et al , 2017Argyriou et al 2018Argyriou et al , 2022Friedman et al 2018), which enable a comparison with the Romanian specimen (see below). Several of the aforementioned genera are from the Early Triassic, an epoch that is characterized by the frequent occurrence of fish fossils preserved threedimensionally in concretions.…”

“…In turn, this lateral process forms the ventrolaterally directed palatal lamina, with the participation of a variable number of dermopalatines (Stensi€ o 1925;Nielsen 1942Nielsen , 1949Hutchinson 1973;Gardiner 1984;V eran 1996;Argyriou et al 2018). In most generalized actinopterygians the palatal lamina forms overlapping sutures with the medial lamina of the maxilla, restricting the movement of the latter (Nielsen 1942(Nielsen , 1949Gardiner 1984;V eran 1996;Argyriou et al 2018Argyriou et al , 2022. V eran's (1996) investigations found additional complexity in the region of the lateral process of the ectopterygoid in some 'primitive' actinopterygians, which could possibly be coded as a separate character state in future phylogenetic works.…”

Late Cretaceous sturgeons (Acipenseridae) from North America, with two new species from the Tanis site in the Hell Creek Formation of North Dakota

“…The order also includes the extinct families †Peipiaosteidae (Late Jurassic to Early Cretaceous, Asia; see Hilton et al, 2021) and †Chondrosteidae (Jurassic, Europe; see Hilton and Forey, 2009) (Grande and Bemis, 1996; Bemis et al, 1997; Hilton and Grande, 2021). Acipenseriformes has been interpreted as the closest extant sister group of the Neopterygii (i.e., gars, bowfins, and teleosts; e.g., Patterson, 1982, Giles et al, 2017, Hughes et al, 2018; see also Grande and Bemis, 1998 and Grande, 2010), with recent phylogenetic analyses reexamining this question (e.g., Argyriou et al, 2018, 2022). Regardless of their exact phylogenetic position at the base of Actinopterygii, this order remains the most taxonomically rich clade of extant actinopterygian fishes outside of Neopterygii.…”

Fitting fangs in a finite face: A novel fang accommodation strategy in a 280‐million‐year‐old ray‐finned fish

“…The late Paleozoic (359.3–251.9 million years ago (mya) (Aretz et al, 2020 ; Henderson, Dunne, & Fasey, 2022 )) represents an important interval for understanding the evolution and diversification of actinopterygians, the ray‐finned fishes. During this time, ray‐finned fishes first evolved a series of innovations that have arisen many times since, including body elongation (Lund & Poplin, 2002 ), body deepening (Gill, 1925 ; Sallan & Coates, 2013 ), and various changes to feeding ranging from adaptations for durophagy (Friedman et al, 2018 ) to changes in jaw articulation (Argyriou et al, 2022 ). Despite the important morphological innovations taking place in the Carboniferous–Permian interval, few ray‐finned fishes of this age have been studied in detail (Argyriou et al, 2022 ; Figueroa et al, 2019 ), suggesting that many additional functional innovations remain unrecognized.…”

“…However, little is known regarding the interactions between the mandibular fangs and the palate in most of these taxa. Taxa with these attributes appear to be dispersed through the stem of the ray‐finned fish tree rather than united as a monophyletic lineage of large‐fanged fossil taxa (Argyriou et al, 2022 ; Figueroa et al, 2019 ; Giles et al, 2017 ; Stack & Gottfried, 2021 ). Few of these fishes are sufficiently well preserved to determine how jaw closing accommodated enlarged dentition.…”